ROLE OF THE GLUTAMINE TRANSAMINASE-OMEGA-AMIDASE PATHWAY AND GLUTAMINASE IN GLUTAMINE DEGRADATION IN RHIZOBIUM-ETLI

Evidence for the participation of the glutamine transaminase-omega-amidase pathway and a glutaminase in the utilization of glutamine in Rhizobium etli has been obtained. The glutamine transaminase preferentially transaminates glyoxylate and pyruvate. Glutamine transaminase activity was similar under all growth conditions tested except on PY (rich medium) where it was low. Glutaminase activity was positively regulated by glutamine and negatively regulated by ammonium and by the carbon source. In R. etli bacteroids, glutamine transaminase was low. whereas glutaminase activity was high. Ammonium liberated from glutamine was assimilated by glutamine synthase, thus leading to the operation of a glutamine cycle that consumes ATP. Our results suggest that glutamine transaminase plays a biosynthetic role in the irreversible synthesis of glycine and alanine, whereas glutaminase plays a catabolic role in the degradation of glutamine to carbon skeletons and to maintain the optimal balance between glutamine and glutamate. The high glutaminase activity found in bacteroids indicates that the degradation of glutamine by this enzyme may play an important role during symbiosis between R. etli and Phaseolus vulgaris.