ASPARAGINE DEGRADATION IN RHIZOBIUM-ETLI

The degradation of asparagine by Rhizobium etli involves asparaginase and aspartate ammonia-lyase (L-aspartase). The two enzymes were shown to be positively regulated by asparagine and negatively regulated by t he carbon source. Asparaginase activity was not regulated by oxygen co ncentration or by nitrogen catabolite repression. Induction of both en zymes by asparagine enables R. etli to utilize asparagine as carbon so urce. Asparaginase may also be involved in maintaining the optimal bal ance between asparagine and aspartate. Aspartase was not involved in t he utilization of aspartate or glutamate as carbon source. The presenc e of high levels of the two enzymes in R. etli bacteroids suggests tha t they may have a role in symbiosis between R. etli and Phaseolus vulg aris.