An enzyme that synthesizes cystathionine and deaminates L-serine.

The first attempt to demonstrate cystathionine synthetase from animal tissues was reported by Binkley (1). This author reported the preparation from rat liver of an extract that catalyzed the synthesis of cystathionine from serine and homocysteine. A second preparation containing cystathionase was utilized for assaying the activity of the synthesis enzyme. Numerous difficulties prevented this attempt at purification from progressing very far. The present work describes a procedure for the purification of cystathionine synthetase from rat liver. The enzyme preparation also catalyzes the deamination of L-serine to pyruvic acid and ammonia. Evidence has been obtained which indicates that both the cystathionine synthetase and serine deaminase activities are due to a single enzyme. A requirement of both enzymic activities for pyridoxal phosphate has been demonstrated.