Abstract
1. Urocanase was partially purified from Pseudomonas aeruginosa and from cat liver, measuring urocanase activity by CPIP reduction.
2. The pH optimum of the urocanase was found to lie between pH 7.0 and 8.0 in both enzyme preparations. Effects of some inhibitors on urocanase were studied.
3. Imidazolonepropionic acid, a proposed early intermediate in urocanate metabolism, is thought to be the starting substrate for the oxidation.
4. The oxidation was completely inhibited by catalase, and stimulated by some metals. A lag period in the oxidation was eliminated by the addition of a small amount of hydrogen peroxide. The mechanism of the oxidation is discussed.
5. One group of oxidation products of urocanic acid includes α-keto-glutaric acid amide, formic acid and ammonia. Another is represented by some carbamyl derivatives or their precursor. The occurrence of these compounds in the incubation mixture was demonstrated using urocanic acid-2-C14.
Before this paper was submitted to press, papers of Brown and Kies have appeared (28). They claim that hydantoinpropionic acid arises from imidazolonepropionic acid.
