Biochemistry Department, Rothamsted Experimental Station, AL5 2JQ, Harpenden, Herts, UK.
Planta. 1983 Apr;157(3):245-53. doi: 10.1007/BF00405189.
Two forms of glutamine synthetase (GS) have been purified to apparent homogeneity from the plant fraction of Phaseolus vulgaris root nodules. One of these forms appears identical to the form of the enzyme found in roots but the other is probably specifically associated with the nodule. Free-living Rhizobium phaseoli also contain two forms of GS both of which have different molecular weights from the plant enzymes. Bacteroids contain solely the higher-molecular-weight form of rhizobial GS. There are only minor differences between the plant enzymes in Km or S0.5 values for the synthetase-reaction substrates and both forms have identical molecular weights of the holoenzyme (380,000 daltons) and its sub-units (41,000 daltons). They can be separated by ion-exchange chromatography on diethylaminoethyl-Sephacel and by native polyacrylamide-gel electrophoresis. The only other distinguishing feature observed is that the ratio of transferase: synthetase activity of the root form is threefold greater than that of the nodule-specific GS.
已从菜豆根瘤植物部分中纯化出两种形式的谷氨酰胺合成酶（GS），达到明显的均一性。其中一种形式与在根中发现的酶形式相同，但另一种可能与根瘤特异性相关。自由生活的根瘤菌也含有两种形式的 GS，它们的分子量均与植物酶不同。类菌体仅含有较高分子量的根瘤菌 GS 形式。对于合成酶反应底物，植物酶之间只有 Km 或 S0.5 值的微小差异，并且两种形式的全酶（380,000 道尔顿）及其亚基（41,000 道尔顿）具有相同的分子量。它们可以通过在二乙基氨基乙基-Sephacel 上的离子交换层析和天然聚丙烯酰胺凝胶电泳进行分离。观察到的唯一其他区别特征是，根形式的转移酶：合成酶活性的比值比结节特异性 GS 高三倍。
