Effects of several unusual sulfur-containing amino acids on rat liver cystathionine-gamma-lyase.
1. The mode of inhibition of rat liver cystathionine-gamma-lyase [L-cystathionine cysteine-lyase (deaminating), EC 4.4.1.1] was studied by using several unusual sulfur-containing amino acids newly found in this laboratory. Some cysteine conjugates (CMC, Beta-CEC, HCETC and HCPC) inhibited noncompetitively both homoserine dehydratase and diaminopropionate ammonia-lyase activities, and competitively gamma-cystathionase activity. CMTC exhibited a mixed type inhibition on both homoserine dehydratase and gamma-cystathionase activities, and a noncompetitive inhibition on the diaminopropionate ammonia-lyase activity. Some homocysteine conjugates (CMHC, beta-CEHC and HCEHC) inhibited competitively both the activity of homoserine dehydratase and of gamma-cystathionase, and exhibited a mixed type inhibition on the diaminopropionate ammonia-lyase activity. beta-CEC, CMHC and beta-CEHC were also effective inhibitors to cysteine desulfhydrase activity. 2. Among the other amino acids tested, DL-homocysteine and D-cysteine, irrespective of their concentration, exhibited a mixed type inhibition on the homoserine dehydratase activity. However, they promoted gamma-cystathionase activity at their lower concentrations and inhibited at their higher concentrations, more so than cystathionine. DL-alpha-Aminobutyric acid was a weak competitive inhibitor of the homoserine dehydratase, gamma-cystathionase and diaminopropionate ammonia-lyase activities. DL-alpha-Aminopimeric acid has the same chain length as beta-CEC, CMHC and CMTC, but it showed a very weak inhibitory effect compared with the latter sulfur-containing compounds. L-Methionine, DL-methionine sulfoxide, L-ethionine, L-cysteic acid, L-aspartic acid, L-asparagine, L-glutamic acid, L-glutamine, D-alanine, beta-alanine, L-ornithine and L-lysine had little or no effect on any activities of the enzyme preparation. These results were discussed in relation to the catalytic center of cystathionine-gamma-lyase.
D000603:Amino Acids, Sulfur / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D003542:Cystathionine gamma-Lyase / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008190:Lyases / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats
D000603:Amino Acids, Sulfur; D008190:Lyases; D003542:Cystathionine gamma-Lyase