Purification and properties of a cytosolic glutamine synthetase expressed in Nicotiana plumbaginifolia cultured cells

Glutamine synthetase (EC 6.3.1.2) was purified and characterized from leaf protoplast-derived suspension cultured cells of Nicotiana plumbaginifolia. Maximal specific activity observed reflected a purification of over 1 500-fold, with a yield of about 40 %. The native protein appeared to be an octamer, with subunits of a molecular mass of 37 kDa. Subcellular fractionation experiments accounted for a cytosolic localization of the enzyme. No evidence for multiple enzyme forms was found following either anion-exchange chromatography or native polyacrylamide gel electrophoresis. Results also suggest that in the absence of intercellular transport, type-1 glutamine synthetase may function preferentially to assimilate ammonia from primary nitrate reduction.