Abstract
Light-independent protochlorophyllide reductase (DPOR) is an oxygen-sensitive enzyme catalyzing the D-ring reduction of protochlorophyllide (Pchlide) producing chlorophyllide a, the direct precursor of chlorophyll a. DPOR from Rhodobacter capsulatus consists of two separable components, BchL and BchNB. In this study, we will present an assay system for individual components of DPOR for the first time. The BchL activity in a crude extract was successfully determined by mixing with another crude extract containing an excess amount of BchNB, and the BchNB activity was done by mixing with an extract containing an excess amount of BchL. Using this assay system, we found that only the BchL activity is sensitive to oxygen while the BchNB activity is stable on exposure to the air. An EPR analysis suggested that the purified BchL carries a [4Fe-4S] cluster, which is similar to the oxygen-labile cluster of nitrogenase Fe-protein. Structural similarity between DPOR and nitrogenase will be discussed.
