Inactivation of the NADH-dependent activities of nitrate reductase by ferrate.

Nitrate reductase (EC 1.6.6.1) from Chlorella vulgaris, a flavin-cytochrome-molybdenum enzyme, catalyses two types of partial reactions: reduction of exogenous cytochrome c by NADH and reduction of nitrate to nitrite by reduced methyl viologen (reduced 1,1'-dimethyl-4,4'-dipyridine dichloride). Ferrate, an analogue of orthophosphate acting on the phosphate-binding region of the enzymes, abolishes the NADH-nitrate reductase as well as the NADH-cytochrome c activities. In addition, the ability of NADH to reduce the endogenous cytochrome b component of the enzyme is also impaired. The reduction of nitrate by reduced methyl viologen is only partially affected. The results indicate that the ferrate primarily disrupts the NADH site.