氨和谷氨酰胺对浑球红假单胞菌（Rhodobacter sphaeroides）固氮酶...

浑球红假单胞菌菌株601具有迅速对外源氨作出“关闭”固氮酶活性的反应。氨对固氮酶的抑制作用,可被谷氨酰胺合成酶(GS)抑制剂MSX所解除。反之,加入Glu代谢抑制剂DON,可延长氨抑制的持续时间。Gln对固氮酶也有抑制作用。在脱腺苷化GS的透性细胞中,加入Gln可抑制固氮酶活性,同时,GS腺苷化状态提高。然而,氨则对透性细胞的固氮酶活性和GS腺苷化状态没有影响。

Effects of NH_4~ and Glutamine on the Regulation of Nitrogenase Activity in Rhodobacter sphaeroides

Although the final result of ammoniainhibition of nitrogenase activity in phototro-phic bacteria is now fairly well understood,there is very little information about theevents leading to the modification of the ironprotein. The aim of this paper was to learnmore about the factors that influence the ironprotein modification system. Nitrogenase activity in Rhodobacter spha-eroides strain 601 was subjected to a rapidswitch-off in response to exogenous ammonia(Fig. 1). However, the inhibition caused byammonia was prevented by methionine sul-phoximine, a glutamine synthetase inhibitor(Fig. 2). On the other hand, the inhibitorof glutamine metabolism, 6-diazo-5-oxo-L-norleucine, prolonged the duration of ammoniaswitch-off (Table 1). The inhibition of ni-trogenase activity induced by glutamine ap-pears to be simillar to ammonia switch-off(Fig. 3). It was shown that the inhibition ofnitrogenase activity by ammonia or glutaminein the cells was parallel to the changes ofthe adenylylation state of glutamine synthe-tase. Addition of glutamine to the toluene-treated cells (glutamine synthetase was deade-nylylated) resulted in a decrease of nitrogena.se activity, whereas the correspounding va-lues for the increasing adenylylation of glu-tamine synthetase. However, addition of am-monia to the toluene-treated cells neitherreduced nitrogenase activity nor inducedadenylylation of glutamine synthetase (Table2). From the above results, the possible re-gulatory mechanism of nitrogenase activitywas discussed.