Rat Liver ^ω-Amidase. Purification and Properties

The ω-amidase from rat liver has been purified to homogeneity. The native enzyme, mol wt 58,000, can be dissociated into subunits of mol wt 27,000-28,000 by treatment with 7 m guanidine hydrochloride or 7 m urea. A study of the substrate specificity of the enzyme revealed that in addition to hydrolyzing α-ketoglutaramate, glutaramate.and succinamate, the enzyme also hydrolyzes the monomethyl and ethyl esters of α-ketoglutarate (τ esters), succinate, and glutarate. In addition to the hydrolytic reactions the enzyme catalyzes hydroxaminolysis and transamidation with esters and amides. Studies on the nature of the reaction of α-ketoglutaramate as a function of pH revealed that below pH 8, the rate-limiting step of the ω-amidase reaction could be the nonenzymatic conversion of 5-hydroxypyroglutamate into a-ketoglutaramate. This latter finding is discussed in terms of its possible physiological significance.