title: Identification of the essential cysteine residue in Klebsiella aerogenes urease.
abstract: During reaction with [14C]iodoacetamide at pH 6.3, radioactivity was incorporated primarily into a single Klebsiella aerogenes urease peptide concomitant with activity loss. This peptide was protected from modification at pH 6.3 by inclusion of phosphate, a competitive inhibitor of urease, which also protected the enzyme from inactivation. At pH 8.5, several peptides were alkylated; however, modification of one peptide, identical to that modified at pH 6.3, paralleled activity loss. The N-terminal amino acid sequence and composition of the peptide containing the essential thiol was determined. Previous enzyme inactivation studies of K. aerogenes urease could not distinguish whether one or two essential thiols were present per active site (Todd, M. J., and Hausinger, R. P. (1991) J. Biol. Chem. 266, 10260-10267); we conclude that there is a single essential thiol present and identify this residue as Cys319 in the large subunit of the heteropolymeric enzyme.
authors.affiliation: Department of Biochemistry, Michigan State University, East Lansing 48824.
authors.forename: M J
authors.initials: MJ
authors.lastname: Todd
authors.forename: R P
authors.initials: RP
authors.lastname: Hausinger
mesh_terms: D000595:Amino Acid Sequence; D003545:Cysteine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D008969:Molecular Sequence Data; D009943:Organophosphorus Compounds / Q000737:chemistry; D010449:Peptide Mapping; D012689:Sequence Homology, Nucleic Acid; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014357:Trypsin; D014510:Urease / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D009943:Organophosphorus Compounds; D013438:Sulfhydryl Compounds; D014357:Trypsin; D014510:Urease; D003545:Cysteine