Activation of Enzymes Iii. the R6le of Metal Ions in the Activation of Ar- Ginase. the Hydrolysis of Arginine Induced by Certain Metal Ions with Urease

Earlier papers from this laboratory have dealt with the activation of urease (1) and of papain (2), with emphasis, particularly, upon reversible inactivations by oxidizing agents and by certain organometallic compounds. This communication describes an investigation of the markedly differing activation chemistry of the enzyme, arginase. There is stressed the conspicuous Ale apparently played by metal ions in the arginase-arginine reaction, a study of which has disclosed the conditions under which hydrolysis of arginine may be extensive when induced only by certain metal ions with ureme. Although enzyme literature is replete with descriptions of the activating and inactivating effects of various reagents (cf. (3)), there have appeared only recently reports of investigations in which has been attained a measure of success in the correlation of some of these effects in terms of a rational chemistry. Progress has been impeded in part by the difficulty of obtaining most enzymes in a state of even approximate purity or in the reproduction by different workers of crude enzyme preparations possessing sufficiently constant behavior. For our initial studies in this field we selected crystalline urease and papain, the properties of which promised relative freedom from these difficulties. Controlled inactivations of these enzymes by various oxidizing agents were found to be extensively reversible, the reversals being effected by a number of reducing substances. The inactivating effects of cuprous oxide and certain organic