INVOLVEMENT OF OXYGEN IN CHLORELLA-FUSCA NITRATE REDUCTASE INACTIVATION BY REDUCED NICOTINAMIDE ADENINE-DINUCLEOTIDE

In vitro inactivation of C. fusca NADH-nitrate reductase can be obtained by preincubation of the enzyme with reduced nicotinamide adenine dinucleotide. ADP cooperates with NADH in this inactivation. Anaerobic experiments reveal that O2 is required to obtain inactivation of nitrate reductase by preincubation with NADH, alone or in the presence of ADP. Moreover, inactivation is prevented if superoxide dimutase and/or catalase are included in the preincubation mixture. The presence of hydrogen peroxide in the preincubation mixture increases the sensitivity of nitrate reductase to its inactivation by NADH. In vivo inactivation of C. fusca NADH-nitrate reductase by addition of methylamine to the cells appears to depend on the intracellular catalase activity levels.