The parental structure of bacteriochlorophyll a, bacteriochlorin, is formed by a sequential operation of two nitrogenase-like enzymes, dark-operative protochlorophyllide oxidoreductase (DPOR) and chlorophyllide alpha oxidoreductase (COR). Both DPOR and COR consist of two components, Fe protein and MoFe protein cognates. Here we determined kinetic parameters of COR and established the reconstitution system for the formation of bacteriochlorin (3-vinyl bacteriochlorophyllide a) from porphyrin (protochlorophyllide) with purified components of DPOR and COR from Rhodobacter capsulatus. This reconstitution system confirmed the recent finding that COR catalyzes 8-vinyl reduction of 8-vinyl chlorophyllide a in addition to the known activity of C7=C8 double bond reduction, and provides a promising model to investigate how two nitrogenase-like enzymes are coordinated in bacteriochlorophyll biosynthesis. (C) 2014 Elsevier Inc. All rights reserved.