EFFECTS OF CYSTEINE ON CELLULAR-ACTIVITY OF DISSIMILATORY NITRATE REDUCTASE IN PSEUDOMONAS-DENITRIFICANS

Dissimilatory nitrate reductase activity in Pseudomonas denitrificans grown under denitrifying conditions was markedly decreased upon incubation of the cells with Cys or GSH. The activity of the enzyme was also low in the membrane fraction isolated from the Cys-treated cells, indicating that the decrease in enzyme activity was due to the inactivation of the enzyme. Cys appeared to exert its effect, at least in part, after conversion to GSH as judged by the stimulation of the Cys effect by concomitant addition of Glu, although even a trace of GSH could not be detected in the cells presumably owing to the high activity of GSH consumption. The inactivating effect of Cvs on the enzyme was found to compete with the activating effect of Na+ that had been reported previously, suggesting the presence of a natural mechanism controlling nitrite accumulation in the environment.