Modulation of different forms of glutamine synthetases inRhizobium phaseoli and their possible role in nitrogen fixation

Abstract

The effect of a number of compounds structurally related to glutamic acid and other nitrogenous compounds on the composition of three forms of glutamine synthetase (GS) inRhizobium phaseoli has been examined in detail. Amino acids like glutamic acid, glutamine, and a fixed source of nitrogen like ammonium chloride did not alter the relative glutamine synthetase composition.l-Methioninedl-sulfoximine (MSX), a glutamate analogue, significantly repressed the synthesis of GSIII to a greater extent.β,N-oxalylα,β-diaminopropionic acid (ODAP), another glutamate analogue, selectively stimulated the synthesis of GSII, and the effect of ODAP on GSII synthesis was greatly enhanced in the presence of ethylenediamine or ammonium chloride. Ethylenediamine itself caused a predominant synthesis of GSIII.β-Cyanoalanine-grownR. phaseoli did not synthesize GSI. The synthesis of the three different glutamine synthetases can thus be differentially modulated.