光与氨对Rhodopseudomonas capsulata固氮活性的调节

光强是调节氨瞬间抑制Rps.capsulata光合固氮活性的一个因子。与弱光(500 lx)比较,强光(30000 lx)对固氮活性氨抑的启动推迟。被氨抑制了的固氮活性在强光下较在弱光下提前解抑。经光合作用解联剂处理的菌体,强光拮抗固氮活性氨抑的现象消失。菌体ATP库水平分析表明:在氨关闭固氮活性时,库量升高。氨的同化被阻抑时,氨对光合固氮的瞬间抑制消失,菌体ATP库保持恒定。对光强与氨抑制固氮活性之间可能涉及的机制进行了探讨。

REGULATION OF NITROGENASE ACTMTY BY LIGHT AND NH_4~+ IN RHODOPSEUDOMONAS CAPSULATA

Light intensity, which is known to be critical in photosynthetic nitrogen fixation, was shown here also to be able to affect the regulation of nitrogenase activity by NH_4~+ in Rhodopseudomonas capsulata. At low light intensity the inhibition of nitrogenase activity by NH_4~+ began immediately after the addition at a high rate. In strong light, the inhibition of nitrogenase activity in response to NH_4~+ was delayed. NH_4~+-inhibition of nitrogenase in weak light was completely relieved by increasing the light intensity. The antagonistic effects of the strong light on the NH_4~+ switch-off process disappeared, when the cells were exposed to uncouplers of photosynthesis. Direct measurement of ATP pool after NH_4~+ switching-off nitrogenase activity showed high level of intracellular ATP. Methionine sulfoximine, an inhibitor of NH_4~+ assimilation, blocked the inhibitory effect of NH_4~+ on the nitrogenase activity, in that case, the intracellular ATP concentration was unchanged. An overlapping mechanism possibly involved in NH_4~+ -induced switch-off of nitrogenase activity and the influence of the light intensity on it was discussed.