Nicotinamide is a specific inhibitor of dark-operative protochlorophyllide oxidoreductase, a nitrogenase-like enzyme, from Rhodobacter capsulatus

Abstract

Dark-operative protochlorophyllide oxidoreductase (DPOR) is a nitrogenase-like enzyme consisting of two components, L-protein as a reductase component and NB-protein as a catalytic component. Elucidation of the crystal structures of NB-protein (Muraki et al., Nature 2010, 465: 110-114) has enabled us to study its reaction mechanism in combination with biochemical analysis. Here we demonstrate that nicotinamide (NA) inhibits DPOR activity by blocking the electron transfer from L-protein to NB-protein. A reaction scheme of DPOR, in which the binding of protochlorophyllide (Pchlide) to the NB-protein precedes the electron transfer from the L-protein, is proposed based on the NA effects.

Keywords: Bacteriochlorophyll; Bchl; Chl; Chlide; Chlorophyll; DPOR; FeS cluster; LPOR; NA; Nitrogenase; Pchlide; Protochlorophyllide; bacteriochlorophyll; chlorophyll; chlorophyllide a; dark-operative protochlorophyllide oxidoreductase; light-dependent protochlorophyllide oxidoreductase; nicotinamide; protochlorophyllide.