Nitrate reductase from Spinacea oleracea. Effects of sulfhydryl-group reagents on the activities of the complex and the inactivation by NADH

Abstract

Sulfhydryl-group reagents inactive the nitrate reductase complex from Spinacea oleracea. Most of the reagents used inactivate selectively the NADH-diaphorase moiety. However, at higher concentrations of reagent the FNH 2-nitrate reductase is also affected. Enzyme preparations inactivated by p-hydroxy-mercuribenzoate can be reactivated by dithioerythritol. Nitrate reductase lacking NADH-diaphorase activity, after treatment with p-hydroxymercuribenzoate, is inactivated in its FNH 2-nitrate reductase moiety by NADH in the same way as the untreated preparation. This apparent independence of the NADH-inactivation process from NADH-diaphorase activity supports the postulated existence of a binding site for pyridine nucleotides implicated in NADH-inactivation and different from the diaphorase catalytic site.