Urocanase properties

Rao, D.R., Greenberg, D.M. Studies on the enzymic decomposition of urocanic acid. II. Properties of products of urocanase reaction. Biochim. biophys. Acta (Amst.) 43, 404-418 (1960)... 

Properties. Histidase and urocanase were separated from each other by Takeuchi by taking advantage of the observation that heating liver extract at 55°C. for 30 minutes and then acidifying the solution caused the histidase to be thrown down in the voluminous precipitate formed, while the urocanase remained in the supernatant liquid. 

In studying the properties of histidase, in order to minimize the interference of urocanase, the alkaline pH of 9.3 is commonly employed. At this pH urocanase activity is reduced sufficiently to allow the histidase determination of relatively crude enzyme preparations. 

When a crude liver extract is added to the purified urocanase, decomposition of urocanic acid proceeds to W-formimino-L-glutamic acid. The enzyme carrying out this stage of the reaction has been named imidazolonepropionic acid hydrolase. In view of the fact that im-idazolonepropionic acid has not been isolated and study of the hydrolysis reaction can only be performed in incubation mixtures in which urocanic acid is reacted with purified urocanase very little is known about the properties of the hydrolase enzyme. This enzyme has been purified about tenfold by ammonium sulfate fractionation in our laboratory (266). The enzyme activity is shown by an acceleration in the rate of the decomposition of the 264 my absorption. The product formed was shown to be formimino glutamic acid by testing with purified formiminotransferase which is specific for this compound. 

---