JMSSJ On-line, Vol. 51 (2003) No. 5, pp. 504-508
Mass Spectrometric Study of Protein Molecular Diversity:
Posttranslational Modification of Liver Glutamine Synthetase in Hepatoma
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    Yasuhiro KURAMITSU*a), Toshifusa TODA b), Masaaki OKA c),Kiwamu OKITA d), and Kazuyuki NAKAMURA a), e)

    *a) Department of Biochemistry and Biomolecular Recognition, Yamaguchi University School of Medicine (Minami-kogushi 1-1-1, Ube, Yamaguchi 755-8505, Japan) b) Proteome Research Center, Tokyo Metropolitan Institute of Gerontology (Sakaemati 35-2, Itabashi, Tokyo 173-0015, Japan) c) Department of Gastro-intestinal Surgery and Advanced Molecular Applied Medicine, Yamaguchi University School of Medicine (Minami-kogushi 1-1-1, Ube, Yamaguchi 755-8505, Japan) d) Department of Gastro-intestinal Medicine and Advanced Molecular Applied Medicine, Yamaguchi University School of Medicine (Minami-kogushi 1-1-1, Ube, Yamaguchi 755-8505, Japan) e) Central Laboratory for Biomedical Research and Education (Minami-kogushi 1-1-1, Ube, Yamaguchi 755-8505, Japan)
Mass spectrometric analysis of molecular diversity of human liver glutamine synthetase (GS) is described. An acidic isoform of GS, which is highly expressed in human well-differentiated hepatocellular carcinoma, and that caused by posttranslational modification of protein phosphorylation which was determined by post source decay (PSD) analysis using matrix assisted laser deionization/ionization-time of flight (MALDI-TOF) mass spectrometry. The peptide mass fingerprinting (PMF) of tryptic peptides of the GS isoform showed a loss of the signal of 899.5 Da corresponding a peptide of SASIRIPR and a gain of the signal of 1,059.5 Da which was submitted to PSD analysis. The PSD analysis showed the neutral loss by elimination of two phosphate groups which were supposed to be on serine residues of 899.5 Da peptide from serine 320 to arginine 327 in GS. The PMF followed by PSD analysis is useful for the determination of phosphorylation site(s) of proteins showing molecular heterogeneity.
Key words: Proteome, Hepatitis C virus (HCV), Hepatocellular carcinoma (HCC), Glutamine synthetase (GS)
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