Noridge N A, Benson D R
J Bacteriol. 1986 Apr;166(1):301-5. doi: 10.1128/jb.166.1.301-305.1986.
Under N2-fixing conditions in aerobic culture and in symbiosis, frankiae produce spherical, multicellular structures that have been called vesicles. The vesicles have been proposed as the site of nitrogen fixation. We isolated vesicles by using density centrifugation in a single-step sucrose gradient. Vesicles migrated out of 50% (wt/vol) sucrose and banded at the 40 to 50% sucrose interface; they were intact, as assessed by transmission electron microscopy, and were free of hyphal contamination. Specific activities of nitrogenase in vesicles prepared anaerobically were up to 100-fold greater than the specific activity of the largely hyphal pellet, depending on the recovery of vesicles. All of the activity in the pellet could be accounted for by the number of vesicles present in the pellet. Glutamine synthetase activity in crude extracts of vesicles was extremely low.
在需氧培养和共生的固氮条件下，弗兰克氏菌会产生被称为泡囊的球形多细胞结构。泡囊被认为是固氮的场所。我们通过在单步蔗糖梯度中进行密度离心来分离泡囊。泡囊从50%（重量/体积）的蔗糖中迁移出来，并在40%至50%的蔗糖界面处形成条带；通过透射电子显微镜评估，它们是完整的，且没有菌丝污染。根据泡囊的回收率，厌氧制备的泡囊中固氮酶的比活性比主要由菌丝组成的沉淀的比活性高多达100倍。沉淀中的所有活性都可以由沉淀中存在的泡囊数量来解释。泡囊粗提物中的谷氨酰胺合成酶活性极低。
