Reactivation Mechanisms Research Articles

The reactivation of nitrate reductase from spinach (Spinacia oleracea L.) inactivated by NADH and cyanide, using trivalent manganese either generated by illuminated chloroplasts or as manganipyrophosphate

Nitrate reductase of spinach (Spinacia oleracea L.) leaves which had been inactivated in vitro by treatment with NADH and cyanide, was reactivated by incubation with oxidant systems and measured as FMNH2-dependent activity. Reactivation was produced with trivalent manganese compounds represented either by manganipyrophosphate or produced by oxidation of Mn(2+) ions in the presence of illuminated chloroplasts and compared with reactivation obtained with ferricyanide. Reactivation in the chloroplast system was equivalent to that with ferricyanide when orthophosphate was used but was variable and weak in the presence of pyrophosphate, although manganipyrophosphate was formed, freely. Reactivation by manganipyrophosphate in dark reaction conditions was less effective than with ferricyanide but was not inhibited by the addition of pyrophosphate. Reactivation with illuminated unheated chloroplasts was dependent on added manganese and oxidation of manganese in the presence of pyrophosphate was abolished by boiling the chloroplasts. In the presence of orthophosphate however, boiled, illuminated chloroplasts reactivated the enzyme in the absence of added manganese. Reactivation occurred spontaneously in air, more slowly than with the other oxidants, but to a similar extent to that produced by manganipyrophosphate. The results provide a possible model for physiological reactivation mechanisms.

Repair of ultraviolet lesions and induction of λ prophage

Dose-induction functions for several λ-lysogenic strains of Escherichia coli with different reactivation mechanisms have been measured. It is found that dark-reactivation (DR) reactivates inducing lesions but K reactivation does not. For DR-positive strains the fraction induced is proportional to the UV dose under conditions of complete DR, while for DR-negative strains the fraction induced is proportional to about the fourth power of the UV dose. It is concluded that several dark-reactivable lesions cooperate in λ induction, while a single nonreactivable lesion can probably induce the prophage. Therefore the pathway to induction from reactivable UV lesions appears to be different from the pathway to induction from nonreactivable ones. Low UV doses kill Bs-1(λ) and BB(λ) cells without inducing the prophage, but higher doses induce these dead cells. It is concluded that killing and induction by UV are independent processes. The formal target size for induction is much smaller than that for killing.

Dark- and K-reactivation in UV irradiated Escherichia coli.

UV survival of E. coli strains with different sensitivities has been measured under several post-irradiation conditions, which have been found to influence only the efficiency of two known reactivation mechanisms.