Alternative Electron Donors for the Nitrogenase-like Dark-Operative Protochlorophyllide Oxidoreductase (DPOR)

Abstract

Sharing structural and mechanistic properties with the dinitrogen-fixing enzyme nitrogenase, dark-operative protochlorophyllide oxidoreductase (DPOR) participates in the biosynthesis of bacteriochlorophyll, subsequently enabling photosynthesis by photosynthetic bacteria. In contrast to the light-dependent POR, electron transfer in DPOR is coupled to the hydrolysis of adenosine triphosphate for the two-electron stereoselective reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), a coupling also employed by nitrogenases for the multielectron reduction of dinitrogen to ammonia. The importance of adenosine triphosphate hydrolysis is not fully understood for these enzymes, and electrochemistry is a valuable technique to regulate and/or monitor electron delivery to these enzymes. Here, we report three alternative electron donors that support protochlorophyllide reduction in the DPOR system, which could also enable electroenzymatic studies of DPOR. We demonstrate the turnover of DPOR within a spectroelectrochemical configuration, permitting the formation of Chlide to be followed and coupled to electron utilization by DPOR.