SUMMARY: had low levels of nitrogenase activity and antigenic cross reacting material to both nitrogenase components when grown, or when the operons were derepressed, under Mo-deficient conditions. When molybdate (100 λ) was added to Mo-deprived cultures shortly after initiating derepression of nitrogenase, activity was rapidly restored and reached up to 60% of that of control cultures supplied with molybdate throughout derepression. Restoration of activity was prevented by chloramphenicol (200 λg ml ) but not by tetracycline (100 λg ml ), although both compounds inhibited general protein synthesis at these concentrations. Expression of the structural genes was not rapidly stimulated by added molybdate, so the rapid stimulation of activity was due to the activation of a low level of apoprotein present in Mo-deprived cultures. After 16 h of Mo-deprivation, suspensions no longer responded rapidly to added molybdate, consistent with the finding that, when further protein synthesis was inhibited by the addition of chloramphenicol after 4 h Mo-deprivation, polypeptides of the MoFe protein (Kp1) but not the Fe protein (Kp2) of nitrogenase were degraded within the following 18 h.


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