A liver enzyme, requiring pyridoxal phosphate as coenzyme, which catalyzes the hydrolysis of
l-cystathionine to
l-cysteine and 2-ketobutyrate, releasing NH
3; also catalyzes formation of 2-ketobutyrate from
l-homoserine, of pyruvate (and NH
3 and H
2S) from
l-cysteine, and of thiocysteine, pyruvate, and NH
3 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.