Glutamine synthetase (EC 220.127.116.11) 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
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