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-ami dase pathway and a glutaminase in the utilization of glutamine in Rhiz obium etli has been obtained. The glutamine transaminase preferentiall y transaminates glyoxylate and pyruvate. Glutamine transaminase activi ty was similar under all growth conditions tested except on PY (rich m edium) where it was low. Glutaminase activity was positively regulated by glutamine and negatively regulated by ammonium and by the carbon s ource. In R. etli bacteroids, glutamine transaminase was low. whereas glutaminase activity was high. Ammonium liberated from glutamine was a ssimilated by glutamine synthase, thus leading to the operation of a g lutamine cycle that consumes ATP. Our results suggest that glutamine t ransaminase plays a biosynthetic role in the irreversible synthesis of glycine and alanine, whereas glutaminase plays a catabolic role in th e degradation of glutamine to carbon skeletons and to maintain the opt imal balance between glutamine and glutamate. The high glutaminase act ivity 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.