Purification and partial characterization of glutamine synthetase from root nodules of faba bean

TL;DRAbstract

Glutamine synthetase (GS, EC 6.1.3.2) from the plant fraction of Vicia faba L. nodules was purified to apparent homogeneity using Sepharose-anthranilic acid affinity chromatography. The enzyme is composed of three 40 kD polypeptides and has a native molecular weight of 310-330 kD, determined by gel filtration chromatography and native gradient polyacrylamide gel electrophoresis, respectively, and showed cross-reactivity with antibodies obtained against Phaseolus vulgaris nodule GS. Two isoenzymes, GSn-1 and Gsn-2, were separated in nodules by anion-exchange chromatography on Q-Sepharose, while just one form could be identified in roots, all the isoenzymes being identical in subunit composition and native molecular weight. The transferase to semibiosynthetic activity ratio of all three GS forms was found to be unusually low. Glutamine synthetase abundance in nodules was quantified by densitometry, representing about 5% of total soluble protein extracted. Possible significance of these a

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