Glutamine synthetase II (GSII) was purified to homogeneity from biovar and characterized. The sequence of 26 amino acid residues from the amino-terminal end of the protein showed high similarity with the sequence of GSII from or from . Non-denaturing PAGE showed that GSII, either in crude extracts or in the pure state, was a mixture of an octamer and a tetramer and that under specific conditions the octamer/tetramer ratio could be modified in either direction. The pure enzyme was used to raise an antiserum which was highly specific. Addition of NHCl to a bacterial culture derepressed for GSII caused a specific decrease in transferase activity, faster than the one observed when the amount of immunoreactive material was measured by different methods. On the other hand, biosynthetic activity, measured as the rate of ADP or glutamine formation, paralleled the rate of decrease in immunoreactive material. A partially purified enzyme preparation retained this dissociation of kinetic parameters, strongly suggesting a post-translational modification. These findings are discussed with respect to the possible role of GSII in the -legume symbiosis.


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