The Induction of Arginase in Saccharomyces cerevisiae

Saccharomyces cerevisiae can utilize arginine or urea as sole nitrogen source. Arginase degrades arginine to ornithine and urea; urea is catabolized to CO2 and NH3 by the urea degradation system which is composed of a urea carboxylase and an allophanate hydrolase. The arginine analogue, homoarginine, was shown to function as a non-metabolizable inducer of arginase; it is also a competitive inhibitor of this enzyme. Studies on the induction of arginase and of the urea degradation system in a wild type yeast strain grown on minimal medium with ammonia as the nitrogen source have shown that: (a) arginine induces both activities, (b) urea induces only the urea degradation system, (c) homoarginine induces only arginase, and (d) the removal of ammonia, i.e. nitrogen starvation, results in the production of both activities. Starvation of an arginine auxotroph for both arginine and nitrogen does not result in the synthesis of arginase, unless the nonmetabolizable inducer, homoarginine, is added. The urea degradation system is induced by urea but not by arginine in an arginase-negative mutant. Thus, arginase and the urea degradation system appear to be produced independently of each other; the induction of arginase is contingent upon the presence of arginine, while that of the urea degradation system requires the metabolism of this compound to urea.