Differentiation of Rhizobium japonicum, I. enzymatic comparison of nitrogenase repressed and derepressed free living cells and of bacteroids.

Derepressed free living cells of Rhizobium japonicum strain 61-A-101 with leucine as single nitrogen source develop a maximum nitrogenase activity of 180 nmol C2H4.mg protein -1.H-1 in liquid culture under 2% 2% O2 in the gas phase. Only 10% of this activity is found with no oxygen in the gas phase during a 90 min incubation period. The maximum activity under 2% oxygen in the gas phase is unaffected by addition of 1-100 mM NH+4 and by addition of low concentrations of glutamine (0.36-1.44 mM). Specific activities of alanine dehydrogenase (E.C. 1.4.1.1.) asparatate aminotransferase (E.C. 2.6.1.1.) and, with much lower activities, of GOGAT (E.C. 1.4.1.13) in nitrogenase active free living cells are more similar to bacteroids than to nitrogenase repressed free living cells from liquid culture. The activities in nitrogenase repressed cells were about 50% lower. Glutamine synthetase (E.C. 6.3.1.2.) activity in bacteroids and in nitrogenase active cells were also similar, but only about 25-30% of that found in nitrogenase repressed Rhizobium japonicum cells.