Physiological roles of glutamine synthetases I and II in ammonium assimilation in Rhizobium sp. 32H1

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Abstract
The 2 glutamine synthetases of Rhizobium sp. 32H1 appear to be structurally and functionally distinct. Glutamine synthetase I was reversibly adenylylated, and its synthesis was repressed only 2-fold by ammonium. When in the unadenylylated configuration, it was the enzyme which allowed the organism to grow, although marginally, on ammonium as a N source. There is no evidence to suggest that the 2nd enzyme, glutamine synthetase II, is regulated by adenylylation. This enzyme was repressed at least 50-fold by even low amounts of ammonium. Glutamine synthetase II does not seem to function in ammonium assimilation but rather in purine biosynthesis.