Effect of methionine sulfoximine in nitrogenase activity by ammonia and glutamine in Rhodopseudomonas sphaeroides
1988
Lee, H.J. (Donga Univ., Pusan (Korea R.). Coll. of Natural Science)
The effect of ammonia and glutamine on nitrogenase activity of Rhodopseudomonas sphaeroides was examined. The nitrogenase activity of this strain was inhibited by ammonia and glutamine. When ammonia and glutamine were exhausted, nitrogenase activity promptly resumed at its original rate. Methionine sulfoximine (MSX), irreversible glutamine synthetase (GS) inhibitor, is a structural analogue of glutamate. MSX was used in order to know whether the nitrogenase activity was inhibited by ammonia and glutamine directly or not. The ability of MSX to prevent nitrogenase switch-off by ammonia was found to be dependent upon the phase of culture. When the cells were sampled after 12 hour culture, 500 micro M MSX did not prevent the nitrogenase switch-off by ammonia. Twenty one percent of GS activity was inhibited by 500 micro M of MSX and concentration of released ammonia decreased. But nitrogenase activity was still inhibited by ammonia. However, nitrogenase switch-off after 20 hours was prevented by 100 micro M of MSX. On the other hand, GS activity was inhibited completely by 100 micro M MSX and concentration of released ammonia somewhat increased. But nitrogenase activity was not inhibited. This data indicated that the inhibition of in vivo nitrogenase activity of Rp. sphaeroides by ammonia seemed to be mediated by products of ammonia assimilation rather than by ammonia itself
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