cystathionine γ-lyase

A liver enzyme, requiring pyridoxal phosphate as coenzyme, that catalyzes the hydrolysis of l-cystathionine to l-cysteine and 2-ketobutyrate, releasing NH₃; also catalyzes formation of 2-ketobutyrate from l-homoserine, of pyruvate (and NH₃ and H₂S) from l-cysteine, and of thiocysteine, pyruvate, and NH₃ from cystine. A deficiency of this enzyme results in cystathioninuria. It catalyzes a step in methionine catabolism and in cysteine biosynthesis. SEE ALSO: cystathionine β-lyase. SYN: cystathionase, cysteine desulfhydrase, cystine desulfhydrase, γ-cystathionase, homoserine deaminase, homoserine dehydratase.