title: A purified cysteine conjugate beta-lyase from rat kidney cytosol. Requirement for an alpha-keto acid or an amino acid oxidase for activity and identity with soluble glutamine transaminase K.
abstract: Cysteine conjugate beta-lyase has been purified from rat kidney cytosol. The enzyme is a 100,000-dalton dimer of two 55,000-dalton subunits and has an absorption maximum at 432 nm. The enzyme has phenylalanine alpha-keto-gamma-methiolbutyrate transaminase activity and appears to be identical to rat kidney cytosolic glutamine transaminase K. Metabolism of S-1,2-dichlorovinyl-L-cysteine (DCVC) by the purified enzyme was dependent on the presence of either alpha-keto-gamma-methiolbutyrate or a protein factor which is present in the cytosolic fraction of rat kidney cortex. The protein factor was identified as a flavin containing L-amino acid oxidase which oxidized DCVC to S-(1,2-dichlorovinyl)-3-mercapto-2-oxopropionic acid. S-(1,2-Dichlorovinyl)-3-mercapto-2-oxopropionic acid has not been previously reported as a metabolite of DCVC. The data also show that rat kidney cytosolic glutamine transaminase K catalyzes both a beta-elimination and a transamination reaction with DCVC when alpha-keto-gamma-methiolbutyrate is present and that amino acid oxidase and alpha-keto-gamma-methiolbutyrate stimulate the enzyme activity by providing amino acceptors. When incubations were done with DCVC as substrate in the presence of excess alpha-keto-gamma-methiolbutyrate, the beta-lyase catalyzed beta-elimination and transamination in a ratio of 1:1.3, respectively. Under conditions where most of the alpha-keto-gamma-methiolbutyrate was consumed, the beta-elimination predominated indicating that the S-1,2-dichlorovinyl-3-mercapto-2-oxopropionic acid pool was consumed by transamination after the alpha-keto-gamma-methiolbutyrate had been depleted. The data are discussed with regard to the importance of these pathways as regulators or participants in the toxicity of S-cysteine conjugates.
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000031:analogs & derivatives / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D007672:Kidney Cortex / Q000201:enzymology*; D007700:Kinetics; D050830:L-Amino Acid Oxidase; D008190:Lyases / Q000302:isolation & purification / Q000378:metabolism*; D008297:Male; D008715:Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013053:Spectrophotometry; D000637:Transaminases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: C014632:2-keto-4-methylthiobutyric acid; C039961:S-(1,2-dichlorovinyl)cysteine; D008715:Methionine; D000594:Amino Acid Oxidoreductases; D050830:L-Amino Acid Oxidase; D000637:Transaminases; C427605:glutamine - phenylpyruvate transaminase; C021481:kynurenine-oxoglutarate transaminase; D008190:Lyases; D003545:Cysteine