NB‐protein (BchN–BchB) of dark‐operative protochlorophyllide reductase is the catalytic component containing oxygen‐tolerant Fe–S clusters

Abstract

Dark‐operative protochlorophyllide (Pchlide) oxidoreductase is a nitrogenase‐like enzyme consisting of the two components, L‐protein (BchL‐dimer) and NB‐protein (BchN–BchB‐heterotetramer). Here, we show that NB‐protein is the catalytic component with Fe–S clusters. NB‐protein purified from Rhodobacter capsulatus bound Pchlide that was readily converted to chlorophyllide a upon the addition of L‐protein and Mg‐ATP. The activity of NB‐protein was resistant to the exposure to air. A Pchlide‐free form of NB‐protein purified from a bchH ‐lacking mutant showed an absorption spectrum suggesting the presence of Fe–S centers. Together with the Fe and sulfide contents, these findings suggested that NB‐protein carries two oxygen‐tolerant [4Fe–4S] clusters.