Publications by authors named "M Laura Dántola"

19 Publications

  • Page 1 of 1

Oxidation of tyrosine: Antioxidant mechanism of l-DOPA disclosed.

Free Radic Biol Med 2021 Mar 29;165:360-367. Epub 2021 Jan 29.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET. Casilla de Correo 16, Sucursal 4, (1900) La Plata, Argentina. Electronic address:

Tyrosine is an amino acid related to crucial physiological events and its oxidation, that produce beneficial or detrimental effects on biological systems, has been extensively studied. Degradation of tyrosine often begins with the loss of an electron in an electron transfer reaction in the presence of a suitable electron acceptor. The reaction is facilitated by excited states of the acceptor in photosensitized processes. Several products of tyrosine oxidation have been described, the main ones being 3,4-dihydroxy-l-phenylalanine (commonly known as DOPA) and tyrosine dimers. Here, we report tyrosine recovery from tyrosyl radical, after one-electron oxidation, in the presence of DOPA. We propose that under high oxidative stress the oxidation of tyrosine may be controlled, in part, by one of its oxidation products. Also, we present strong evidence of antioxidant action of DOPA by preventing tyrosine dimerization, one of the most serious oxidative protein modifications, and the origin of structural modifications leading to the loss of protein functionality.
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http://dx.doi.org/10.1016/j.freeradbiomed.2021.01.037DOI Listing
March 2021

Role of Tryptophan Residues in the Toxicity and Photosensitized Inactivation of α-Hemolysin.

Biochemistry 2020 11 27;59(44):4213-4224. Epub 2020 Oct 27.

Instituto de Investigaciones Fisicoquı́micas Teóricas y Aplicadas (INIFTA), Departamento de Quı́mica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Casilla de Correo 16, Sucursal 4, 1900 La Plata, Argentina.

α-Hemolysin (HlyA) is an extracellular protein toxin secreted by uropathogenic strains of that inserts into membranes of eukaryotic cells. The main goal of this work was to investigate the involvement of tryptophan (W) residues in the hemolytic activity of HlyA. We investigated the hemolytic activity of six single-point mutant proteins, in which one of the four Ws was replaced by cysteine (C) or leucine (L). We also analyzed the photoinactivation of HlyA with pterin (Ptr), an endogenous photosensitizer, as a method of unspecific oxidation of W and tyrosine (Y) residues. HlyA photoinactivation was analyzed by ultraviolet-visible spectrophotometry, hemolytic activity measurement, fluorescence spectroscopy, and electrophoretic analysis. The results indicate that Ws are important in the hemolytic process. Specifically, the chemical structure of the amino acid at position 578 is important for the acylation of HlyA at residue K563. Furthermore, the exposure of HlyA to ultraviolet radiation, with energy similar to that experienced under sun exposure, in the presence of Ptr induces the inactivation of the toxin, causing chemical changes in, at least, W and Y, the rate of damage to W residues being faster than that observed for Y residues. This work not only deepens our understanding of the structure-function relationship of the toxin but also introduces the possibility of using photoinactivation of HlyA for potential applications such as obtaining innocuous molecules for vaccine production and the elimination of the toxin from contaminated surfaces and drinking water.
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http://dx.doi.org/10.1021/acs.biochem.0c00660DOI Listing
November 2020

Chemical Modifications of Globular Proteins Phototriggered by an Endogenous Photosensitizer.

Chem Res Toxicol 2019 11 22;32(11):2250-2259. Epub 2019 Oct 22.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas , Universidad Nacional de La Plata, CCT La Plata-CONICET , Casilla de Correo 16, Sucursal 4 , 1900 La Plata , Argentina.

The main goal of the present work was to investigate the damages photoinduced by pterin (Ptr), an endogenous photosensitizer present in human skin under pathological conditions, on a globular protein such as ubiquitin (Ub). Particular attention has been paid on the formation of covalent adducts between Ptr and the protein that can behave as photoantigen and provoke an immune system response. Here, a multifaceted approach including UV-visible spectrophotometry, fluorescence spectroscopy, electrophoresis, size exclusion chromatography, and mass spectrometry is used to establish the Ub changes triggered by UV-A irradiation in the presence of Ptr. Under anaerobic conditions, the only reaction corresponds to the formation of a covalently bound Ptr-Ub adduct that retains the spectroscopic properties of the free photosensitizer. A more complex scheme is observed in air-equilibrated solutions with the occurrence of three different processes, that is, formation of a Ptr-Ub adduct, dimerization, and fragmentation of the protein.
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http://dx.doi.org/10.1021/acs.chemrestox.9b00286DOI Listing
November 2019

Evidence of the effectiveness of Resveratrol in the prevention of guanine one-electron oxidation: possible benefits in cancer prevention.

Phys Chem Chem Phys 2019 Jul;21(29):16190-16197

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata (UNLP), CCT La Plata-CONICET, Diagonal 113 y 64, (1900) La Plata, Argentina.

Over the past few years, the interest in Resveratrol (3,4',5,-trihydroxystilbene, RSV) has increased due to the evidence found of its antioxidant action that protects biomolecules and cells from oxidative damage. The interest has been further exacerbated by the natural presence of RSV in some fruits and derivatives, especially in red wine. In this paper we present evidence of RSV capacity in protecting a deoxynucleotide, an essential constituent of DNA, from one-electron oxidation. This article evaluates the mechanism responsible for the antioxidant action of RSV, after one-electron oxidation of 2'-deoxyguanosine 5'-monophosphate (dGMP), by kinetic analysis during steady-state irradiation and laser flash photolysis experiments. Results showed that RSV protects dGMP by recovering the nucleotide from its radical, which is formed after the reaction of dGMP with the triplet excited state of the photosensitizer. In the absence of RSV, dGMP is irremediably oxidized, and if the damage occurs in dGMP located in DNA molecules, the consequences can be as serious as mutations and subsequent carcinogenic lesions.
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http://dx.doi.org/10.1039/c9cp03027aDOI Listing
July 2019

Photochemistry of tyrosine dimer: when an oxidative lesion of proteins is able to photoinduce further damage.

Photochem Photobiol Sci 2019 Jul;18(7):1732-1741

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET. Casilla de Correo 16, Sucursal 4, (1900) La Plata, Argentina.

The tyrosine dimer (Tyr2), a covalent bond between two tyrosines (Tyr), is one of the most important modifications of the oxidative damage of proteins. This compound is increasingly used as a marker of aging, stress and pathogenesis. At physiological pH, Tyr2 is able to absorb radiation at wavelengths significantly present in the solar radiation and artificial sources of light. As a result, when Tyr2 is formed in vivo, a new chromophore appears in the proteins. Despite the biomedical importance of Tyr2, the information of its photochemical properties is limited due to the drawbacks of its synthesis. Therefore, in this work we demonstrate that at physiological pH, Tyr2 undergoes oxidation upon UV excitation yielding different products which conserve the dimeric structure. During its photodegradation different reactive oxygen species, like hydrogen peroxide, superoxide anion and singlet oxygen, are produced. Otherwise, we demonstrated that Tyr2 is able to sensitize the photodegradation of tyrosine. The results presented in this work confirm that Tyr2 can act as a potential photosensitizer, contributing to the harmful effects of UV-A radiation on biological systems.
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http://dx.doi.org/10.1039/c9pp00182dDOI Listing
July 2019

Editorial: Symposium-in-Print on the Occasion of XIII ELAFOT (XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología).

Photochem Photobiol 2018 09;94(5):827-828

Departamento de Química, Facultad de Ciencias Exactas, Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Universidad Nacional de La Plata (UNLP), CCT La Plata-CONICET, La Plata, Argentina.

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http://dx.doi.org/10.1111/php.12953DOI Listing
September 2018

Effect of pterin impurities on the fluorescence and photochemistry of commercial folic acid.

J Photochem Photobiol B 2018 Apr 9;181:157-163. Epub 2018 Mar 9.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Casilla de Correo 16, Sucursal 4, 1900 La Plata, Argentina. Electronic address:

Folic acid, or pteroyl‑l‑glutamic acid (PteGlu) is a conjugated pterin derivative that is used in dietary supplementation as a source of folates, a group of compounds essential for a variety of physiological functions in humans. Photochemistry of PteGlu is important because folates are not synthesized by mammals, undergo photodegradation and their deficiency is related to many diseases. We have demonstrated that usual commercial PteGlu is unpurified with the unconjugated oxidized pterins 6‑formylpterin (Fop) and 6‑carboxypterin (Cap). These compounds are in such low amounts that a normal chromatographic control would not detect any pterinic contamination. However, the fluorescence of PteGlu solutions is due to the emission of Fop and Cap and the contribution of the PteGlu emission, much lower, is negligible. This is because the fluorescence quantum yield (Φ) of PteGlu is extremely weak compared to the Φ of Fop and Cap. Likewise, the PteGlu photodegradation upon UV-A radiation is an oxidation photosensitized by oxidized unconjugated pterins present in the solution, and not a process initiated by the direct absorption of photons by PteGlu. In brief, the fluorescence and photochemical properties of PteGlu solutions, prepared using commercially available solids, are due to their unconjugated pterins impurities and not to PteGlu itself. This fact calls into question many reported studies on fluorescence and photooxidation of this compound.
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http://dx.doi.org/10.1016/j.jphotobiol.2018.03.007DOI Listing
April 2018

Photooxidation of Tryptophan and Tyrosine Residues in Human Serum Albumin Sensitized by Pterin: A Model for Globular Protein Photodamage in Skin.

Biochemistry 2016 08 18;55(34):4777-86. Epub 2016 Aug 18.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET , Casilla de Correo 16, Sucursal 4, 1900 La Plata, Argentina.

Human serum albumin (HSA) is the most abundant protein in the circulatory system. Oxidized albumin was identified in the skin of patients suffering from vitiligo, a depigmentation disorder in which the protection against ultraviolet (UV) radiation fails because of the lack of melanin. Oxidized pterins, efficient photosensitizers under UV-A irradiation, accumulate in the skin affected by vitiligo. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to induce structural and chemical changes in HSA under UV-A irradiation. Our results showed that Ptr is able to photoinduce oxidation of the protein in at least two amino acid residues: tryptophan (Trp) and tyrosine (Tyr). HSA undergoes oligomerization, yielding protein structures whose molecular weight increases with irradiation time. The protein cross-linking, due to the formation of dimers of Tyr, does not significantly affect the secondary and tertiary structures of HSA. Trp is consumed in the photosensitized process, and N-formylkynurenine was identified as one of its oxidation products. The photosensitization of HSA takes place via a purely dynamic process, which involves the triplet excited state of Ptr. The results presented in this work suggest that protein photodamage mediated by endogenous photosensitizers can significantly contribute to the harmful effects of UV-A radiation on the human skin.
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http://dx.doi.org/10.1021/acs.biochem.6b00420DOI Listing
August 2016

Oxidation of tyrosine photoinduced by pterin in aqueous solution.

Photochem Photobiol 2013 Nov-Dec;89(6):1448-55. Epub 2013 Jun 27.

Departamento de Química, Facultad de Ciencias Exactas, Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Universidad Nacional de La Plata, CCT La Plata-CONICET, La Plata, Argentina.

Pterins, heterocyclic compounds widespread in biological systems, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. Pterins have been previously identified as good photosensitizers under UV-A irradiation. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the oxidation of tyrosine (Tyr) in aqueous solutions. Tyr is an important target in the study of the photodynamic effects of UV-A radiation because it is oxidized by singlet oxygen ((1)O2) and plays a key role in polymerization and cross-linking of proteins. Steady UV-A irradiation of solutions containing Ptr and Tyr led to the consumption of Tyr and dissolved O2, whereas the Ptr concentration remained unchanged. Concomitantly, hydrogen peroxide (H2O2) was produced. By combining different analytical techniques, we could establish that the mechanism of the photosensitized process involves an electron transfer from Tyr to the triplet excited state of Ptr. Mass spectrometry, chromatography and fluorescence were used to analyze the photoproducts. In particular, oxygenated and dimeric compounds were identified.
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http://dx.doi.org/10.1111/php.12099DOI Listing
June 2015

Photosensitization of bovine serum albumin by pterin: a mechanistic study.

J Photochem Photobiol B 2013 Mar 26;120:52-8. Epub 2013 Jan 26.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Casilla de Correo 16, Sucursal 4, 1900 La Plata, Argentina.

Pterins, heterocyclic compounds widespread in biological systems, are able to photoinduce oxidation of DNA and its components. In the present study, we have investigated the photosensitizing properties of pterin (Ptr), the parent compound of oxidized pterins, using bovine serum albumin (BSA) as target. Aqueous solutions of BSA were exposed to UV-A irradiation (350nm) in the presence of Ptr, under various experimental conditions. The photosensitized processes were followed by UV/vis spectrophotometry, an enzymatic method for H2O2 determination and electrophoresis (SDS-PAGE). We present data that demonstrate unequivocally that BSA is damaged by Ptr. Although association between Ptr and the protein was evidenced by steady-state and time-resolved fluorescence measurements, the photosensitized damage takes place via a purely dynamic mechanism, which involves an electron transfer from BSA to the triplet excited state of Ptr, formed after UV-A excitation.
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http://dx.doi.org/10.1016/j.jphotobiol.2013.01.008DOI Listing
March 2013

Mechanism of electron transfer processes photoinduced by lumazine.

Photochem Photobiol Sci 2012 Feb 3;11(2):409-17. Epub 2012 Jan 3.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET. Casilla de Correo 16, Sucursal 4, (1900), La Plata, Argentina.

UV-A (320-400 nm) and UV-B (280-320 nm) radiation causes damage to DNA and other biomolecules through reactions induced by different endogenous or exogenous photosensitizers. Lumazines are heterocyclic compounds present in biological systems as biosynthetic precursors and/or products of metabolic degradation. The parent and unsubstituted compound called lumazine (pteridine-2,4(1,3H)-dione; Lum) is able to act as photosensitizer through electron transfer-initiated oxidations. To get further insight into the mechanisms involved, we have studied in detail the oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) photosensitized by Lum in aqueous solution. After UV-A or UV-B excitation of Lum and formation of its triplet excited state ((3)Lum*), three reaction pathways compete for the deactivation of the latter: intersystem crossing to singlet ground state, energy transfer to O(2), and electron transfer between dAMP and (3)Lum* yielding the corresponding pair of radical ions (Lum˙(-) and dAMP˙(+)). In the following step, the electron transfer from Lum˙(-) to O(2) regenerates Lum and forms the superoxide anion (O(2)˙(-)), which undergoes disproportionation into H(2)O(2) and O(2). Finally dAMP˙(+) participates in subsequent reactions to yield products.
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http://dx.doi.org/10.1039/c1pp05315aDOI Listing
February 2012

Emission properties of dihydropterins in aqueous solutions.

Phys Chem Chem Phys 2011 Apr 15;13(16):7419-25. Epub 2011 Mar 15.

INIFTA, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET., C.C. 16, Suc. 4, (1900) La Plata, Argentina.

Pterins belong to a class of heterocyclic compounds present in a wide range of living systems and accumulate in the skin of patients affected by vitiligo, a depigmentation disorder. The study of the emission of 7,8-dihydropterins is difficult because these compounds are more or less unstable in the presence of O(2) and their solutions are contaminated with oxidized pterins which have much higher fluorescence quantum yields (Φ(F)). In this work, the emission properties of six compounds of the dihydropterin family (6-formyl-7,8-dihydropterin (H(2)Fop), sepiapterin (Sep), 7,8-dihydrobiopterin (H(2)Bip), 7,8-dihydroneopterin (H(2)Nep), 6-hydroxymethyl-7,8-dihydropterin (H(2)Hmp), and 6-methyl-7,8-dihydropterin (H(2)Mep)) have been studied in aqueous solution. The fluorescence characteristics (spectra, Φ(F), lifetimes (τ(F))) of the neutral form of these compounds have been investigated using the single-photon-counting technique. Φ(F) and τ(F) values obtained lie in the ranges 3-9 × 10(-3) and 0.18-0.34 ns, respectively. The results are compared to those previously reported for oxidized pterins.
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http://dx.doi.org/10.1039/c0cp02912bDOI Listing
April 2011

Mechanism of photooxidation of folic acid sensitized by unconjugated pterins.

Photochem Photobiol Sci 2010 Dec 5;9(12):1604-12. Epub 2010 Oct 5.

INIFTA, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET. C.C. 16, Suc. 4, (1900), La Plata, Argentina.

Folic acid, or pteroyl-l-glutamic acid (PteGlu), is a precursor of coenzymes involved in the metabolism of nucleotides and amino acids. PteGlu is composed of three moieties: a 6-methylpterin (Mep) residue, a p-aminobenzoic acid (PABA) residue, and a glutamic acid (Glu) residue. Accumulated evidence indicates that photolysis of PteGlu leads to increased risk of several pathologies. Thus, a study of PteGlu photodegradation can have significant ramifications. When an air-equilibrated aqueous solution of PteGlu is exposed to UV-A radiation, the rate of the degradation increases with irradiation time. The mechanism involved in this "auto-photo-catalytic" effect was investigated in aqueous solutions using a variety of tools. Whereas PteGlu is photostable under anaerobic conditions, it is converted into 6-formylpterin (Fop) and p-aminobenzoyl-l-glutamic acid (PABA-Glu) in the presence of oxygen. As the reaction proceeds and enough Fop accumulates in the solution, a photosensitized electron-transfer process starts, where Fop photoinduces the oxidation of PteGlu to Fop, and H(2)O(2) is formed. This process also takes place with other pterins as photosensitizers. The results are discussed with the context of previous mechanisms for processes photosensitized by pterins, and their biological implications are evaluated.
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http://dx.doi.org/10.1039/c0pp00210kDOI Listing
December 2010

Electron-transfer processes induced by the triplet state of pterins in aqueous solutions.

Free Radic Biol Med 2010 Sep 18;49(6):1014-22. Epub 2010 Jun 18.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, 1900 La Plata, Argentina.

Pterins (Pt) are heterocyclic compounds widespread in living systems. They participate in relevant biological processes, such as metabolic redox reactions, and can photoinduce the oxidation of biomolecules through electron-transfer mechanisms. We have investigated the electron-transfer pathways initiated by excited states of pterin (Ptr) and 6-methylpterin (Mep), selected as model compounds. The experiments were carried out in aqueous solutions under continuous UV-A irradiation, in the presence and in the absence of ethylenediaminetetraacetic acid (EDTA), used as an electron donor. The reactions were followed by UV/Vis spectrophotometry, HPLC, and an enzymatic method for H(2)O(2) determination. The formation of the superoxide anion (O(2)(*-)) was investigated by electron paramagnetic resonance-spin trapping. The triplet excited states of Ptr and Mep are efficient electron acceptors, able to oxidize a Pt molecule in its ground state. The resulting radical anion (Pt(*-)) reacts with dissolved O(2) to yield O(2)(*-), regenerating the pterin. In the presence of EDTA, this reaction competes efficiently with the anaerobic reaction between Pt(*-) and EDTA(*+), yielding the corresponding stable dihydroderivatives H(2)Pt. The effects of EDTA and dissolved O(2) concentrations on the efficiencies of the different competing pathways were analyzed.
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http://dx.doi.org/10.1016/j.freeradbiomed.2010.06.011DOI Listing
September 2010

Quenching of the fluorescence of aromatic pterins by deoxynucleotides.

J Phys Chem A 2009 Mar;113(9):1794-9

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Boulevard 113 y 64, 1900 La Plata, Argentina.

Steady-state and time-resolved studies of the fluorescence of four aromatic unconjugated pterins (pterin (Ptr), 6-(hydroxymethyl)pterin (Hmp), 6-methylpterin (Mep), and 6,7-dimethylpterin (Dmp)) in aqueous solutions in the presence of different nucleotides (2'-deoxyguanosine 5'-monophosphate (dGMP), 2'-deoxyadenosine 5'-monophosphate (dAMP), and 2'-deoxycytosine 5'-monophosphate (dCMP)) have been performed using the single-photon counting technique. The singlet excited states of acid forms of pterins are deactivated by purine nucleotides (dGMP and dAMP) via a combination of dynamic and static processes. The efficiency of the dynamic quenching is high, independently of the nature of the purine base of the nucleotide and of the chemical structure of the substituents linked to the pterin moiety. Analysis of the static quenching indicates that ground-state association between pterins and purine nucleotides takes place, but the formation of the corresponding complexes is significant only at relatively high reactant concentrations. The quenching of the fluorescence of acid forms of pterin derivatives by dCMP, a pyrimidine nucleotide, is slightly less efficient than the quenching by purine nucleotides and is purely dynamic. In alkaline media, the fluorescence quenching is much less efficient than in acidic media, the deactivation by purine nucleotides being purely dynamic, whereas quenching by dCMP is negligible. Possible mechanisms for the quenching of fluorescence of pterin derivatives by the different nucleotides are discussed.
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http://dx.doi.org/10.1021/jp8101496DOI Listing
March 2009

Oxidation of 2'-deoxyguanosine 5'-monophosphate photoinduced by pterin: type I versus type II mechanism.

J Am Chem Soc 2008 Mar 16;130(10):3001-11. Epub 2008 Feb 16.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CONICET, Casilla de Correo 16, Sucursal 4, (1900) La Plata, Argentina.

UV-A radiation (320-400 nm) induces damage to the DNA molecule and its components through different photosensitized reactions. Among these processes, photosensitized oxidations may occur through electron transfer or hydrogen abstraction (type I) and/or the production of singlet molecular oxygen ((1)O2) (type II). Pterins, heterocyclic compounds widespread in biological systems, participate in relevant biological processes and are able to act as photosensitizers. We have investigated the photosensitized oxidation of 2'-deoxyguanosine 5'-monophosphate (dGMP) by pterin (PT) in aqueous solution under UV-A irrradiation. Kinetic analysis was employed to evaluate the participation of both types of mechanism under different pH conditions. The rate constant of (1)O2 total quenching (k(t)) by dGMP was determined by steady-state analysis of the (1)O2 NIR luminescence, whereas the rate constant of the chemical reaction between (1)O2 and dGMP (k(r)) was evaluated from kinetic analysis of concentration profiles obtained by HPLC. The results show that the oxidation of dGMP photosensitized by PT occurs through two competing mechanisms that contribute in different proportions depending on the pH. The dominant mechanism in alkaline media involves the reaction of dGMP with (1)O2 produced by energy transfer from the PT triplet state to molecular oxygen (type II). In contrast, under acidic pH conditions, where PT and the guanine moiety of dGMP are not ionized, the main pathway for dGMP oxidation involves an initial electron transfer between dGMP and the PT triplet state (type I mechanism). The biological implications of the results obtained are also discussed.
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http://dx.doi.org/10.1021/ja075367jDOI Listing
March 2008

Singlet oxygen (O2(1Deltag)) quenching by dihydropterins.

J Phys Chem A 2007 May 3;111(20):4280-8. Epub 2007 May 3.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CONICET, Boulevard 113 y 64 (1900) La Plata, Argentina.

Pterins belong to a class of heterocyclic compounds present in a wide range of living systems. They participate in relevant biological functions and are involved in different photobiological processes. Dihydropterins are one of the biologically active forms of pterins. The photoinduced production and quenching of singlet oxygen (1O2) by a series of dihydropterins (7,8-dihydrobiopterin (DHBPT), 7,8-dihydroneopterin (DHNPT), 6-formyl-7,8-dihydropterin (FDHPT), sepiapterin (SPT), 7,8-dihydrofolic acid (DHFA), and 7,8-dihydroxanthopterin (DHXPT)) in aqueous solution at physiological pH ( approximately 7) were investigated, and the quantum yields of 1O2 production (PhiDelta) and rate constants of total quenching (kt) of 1O2 were determined. Studied compounds do not produce 1O2 under UV-A irradiation and are very efficient 1O2 quenchers. The chemical reactions between 1O2 and dihydropterin derivatives were investigated, and the corresponding rate constants (kr) were found to be particularly high. The oxidized pterin derivatives, biopterin (BPT), neopterin (NPT), 6-formylpterin (FPT), and folic acid (FA), were identified and quantified during the reaction of 1O2 with DHBPT, DHNPT, FDHPT, and DHFA, respectively. Besides the oxidation of the dihydropyrazine ring to yield the corresponding oxidized pterins, a second oxidation pathway, leading to fragmentation of the dihydropterin and formation of non-pterinic products, was identified. Mechanisms and biological implications are discussed.
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http://dx.doi.org/10.1021/jp071278hDOI Listing
May 2007

Photooxidation of pterin in aqueous solutions: biological and biomedical implications.

Chem Biodivers 2004 Nov;1(11):1800-11

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CONICET, CIC Casilla de Correo 16, Sucursal 4, 1900-La Plata, Argentina.

Studies of the photochemical reactivity of pterin (= 2-aminopteridin-4(3H)-one; PT) in acidic (pH 5.0-6.0) and alkaline (pH 10.2-10.8) aqueous solutions have been performed. The photochemical reactions were followed by UV/VIS spectrophotometry, thin layer chromatography (TLC), high-performance liquid chromatography (HPLC), and an enzymatic method for H2O2 determination. PT is not light-sensitive in the absence of molecular oxygen, but it undergoes photooxidation in the presence of O2, yielding several nonpteridinic products. The quantum yields for PT disappearance were found to be 8.2 (+/-0.6) x 10(-4) and 1.2 (+/-0.2) x 10(-3) in acidic and alkaline media, respectively. H2O2 was detected and quantified in irradiated solutions of PT; and its importance from a biomedical point of view is discussed. The rate constant of the chemical reaction between singlet oxygen ((1)O2) and PT was determined to be 2.5 (+/-0.2) x 10(5) l mol(-1) s(-1) in alkaline medium, and the role of (1)O2 in the photooxidation of pterin was evaluated.
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http://dx.doi.org/10.1002/cbdv.200490135DOI Listing
November 2004

Reactivity of conjugated and unconjugated pterins with singlet oxygen (O2(1Deltag)): physical quenching and chemical reaction.

Photochem Photobiol 2007 May-Jun;83(3):526-34

Departamento de Química, Facultad de Ciencias Exactas, Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Universidad Nacional de La Plata, CONICET, La Plata, Argentina.

Pterins (PTs) belong to a class of heterocyclic compounds present in a wide range of living systems. They participate in relevant biological functions and are involved in different photobiological processes. We have investigated the reactivity of conjugated PTs (folic acid [FA], 10-methylfolic acid [MFA], pteroic acid [PA]) and unconjugated PTs (PT, 6-hydroxymethylpterin [HPT], 6-methylpterin [MPT], 6,7-dimethylpterin [DPT], rhamnopterin [RPT]) with singlet oxygen (1O2) in aqueous solutions, and compared the efficiencies of chemical reaction and physical quenching. The chemical reactions between 1O2, produced by photosensitization, and PT derivatives were followed by UV-visible spectrophotometry and high-performance liquid chromatography, and corresponding rate constants (k(r)) were evaluated. Whenever possible, products were identified and quantified. Rate constants of 1O2 total quenching by the PT derivatives investigated were obtained from steady-state 1O2 luminescence measurements. Results show that the behavior of conjugated PTs differs considerably from that of unconjugated derivatives, and the mechanisms of 1O2 physical quenching by these compounds and of their chemical reaction with 1O2 are discussed in relation to their structural features.
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http://dx.doi.org/10.1562/2006-09-15-RA-1041DOI Listing
September 2007