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    An improvement on mass spectrometry-based epigenetic analysis of large histone-derived peptides by using the Ionization Variable Unit interface.
    Anal Biochem 2015 Oct 5;486:14-6. Epub 2015 Jun 5.
    Laboratory for Systems Biology and Medicine, Research Center for Advanced Science and Technology, University of Tokyo, Meguro-Ku, Tokyo 153-8904, Japan. Electronic address:
    Highly protonated histone-derived peptides impede a sufficient mass spectrometry (MS)-based epigenetic analysis because their relatively low m/z, due to a high degree of proton addition to peptides, would make it difficult to analyze the resulting complex MS/MS spectra. To reduce the degree of protonations, we have developed a new interface, the Ionization Variable Unit (IVU), in which peptides are ionized under a vaporized organic solvent. It is demonstrated that the doubly charged histone tail H2B peptide, PEPAKSAPAPKKGSKKAVTKAQKK (m/z 1238.243, +2), which was not detectable before, can be detected by using the IVU interface and sequenced.

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