title: Low pKa lysine residues at the active site of sarcosine oxidase from Corynebacterium sp. U-96.
abstract: Sarcosine oxidase from Corynebacterium sp. U-96 is inactivated by iodoacetamide with the modification of two specific residues. Comparing the amino acid sequence and mass spectra of the peptide fragments containing the modified residues with those from the native enzyme, the modified residues were identified to be lysine. The pKa of these residues were estimated to be 8.5 and 6.7 from the pH dependence of inactivation in the presence and absence of the competitive inhibitor, acetate. These estimated pKa values are much lower than that of the epsilon-amino group of lysine residue. There may be unique microenvironments around these residues that activate their -amino groups to be susceptible to iodoacetamide. A possible role of the lysine residue with pKa 6.7 is discussed.
authors.affiliation: Department of Biosciences, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan. mukoyama@sci.kitasato-u.ac.jp
authors.forename: Etsuko B
authors.initials: EB
authors.lastname: Mukouyama
authors.forename: Mayuko
authors.initials: M
authors.lastname: Oguchi
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kodera
authors.forename: Tadakazu
authors.initials: T
authors.lastname: Maeda
authors.forename: Haruo
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003352:Corynebacterium / Q000145:classification / Q000201:enzymology*; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008239:Lysine / Q000737:chemistry*; D008969:Molecular Sequence Data; D010089:Oxidoreductases, N-Demethylating / Q000737:chemistry*; D011485:Protein Binding; D050879:Sarcosine Oxidase; D013045:Species Specificity
chemical_list: D010089:Oxidoreductases, N-Demethylating; D050879:Sarcosine Oxidase; D008239:Lysine