The glutamine synthetases in soybean root nodules and free-living Rhizobium japonicum

Graduation date: 1978Glutamine synthetase activity is present in both the cytosol and\ud bacteroid fractions of soybean root nodules. Total activity measurements\ud indicate that at least 90% of the activity in nodules is located\ud in the cytosol. Results reported by McParland, et al. (29), showed\ud that many properties of glutamine synthetase from nodule cytosol are\ud similar to those of the enzyme from other eucaryotic organisms. Glutamine\ud synthetase has been purified to more than 90% homogeneity from both\ud the nodule bacteroids and free-living Rhizobium japonicum. The enzymes\ud from these sources displayed similar behavior in all aspects of purification.\ud Experiments in which a snake venom phosphodiesterase was used\ud to remove adenyl groups from the enzymes from both nodule bacteroids and\ud free-living Rhizobium japonicum showed that both glutamine synthetases\ud contain adenylyl groups. In contrast, no evidence has been found for\ud adenylylation or deadenylylation of the cytosol glutamine synthetase.\ud On the basis of behavior during purification and mobility in gel electrophoresis\ud experiments, the bacteroid and cytosol glutamine synthetases\ud are distinctly different while the glutamine synthetases from bacteroids\ud and free-living Rhizobium japonicum had similar electrophoretic and\ud other properties. In many aspects the enzyme from Rhizobia is similar\ud to the glutamine synthetases from Escherichia coli and other gramnegative\ud bacteria. The physiologically active, unadenylylated glutamine\ud synthetase from rhizobia showed greater biosynthetic activity with\ud magnesium than with manganese as the divalent cation activator. The\ud adenylylated enzyme showed a preference for manganese as a divalent\ud cation activator for biosynthetic activity