A crystalline enzyme that cleaves homoserine and cystathionine. III. Coenzyme resolution, activators, and inhibitors.

The authors reported earlier (1) that the crystalline homoaerine deaminase-cystathionase prepared from rat livers contained pyridoxal-5-phosphate as the prosthetic group, and that the bound pyridoxal-5-phosphate is responsible for the absorption maximum at 427 rnp. The present paper deals with resolution of the enzyme into pyridoxal-5-P and catalytically inactive apoenzyme, and the subsequent reconstitution of the active enzyme by combining the two components, thus establishing that pyridoxal-5-P is the coenzyme of this enzyme. In addition, the inhibition and activation of the enzyme by a variety of substances have also been studied.