NADPH:protochlorophyllide oxidoreductase from Gloeobacter violaceus:overexpression,purification and preliminary characterization

Abstract

The cyanobacterium Gloeobacter violaceus is different from other cyanobacteria in that it doesn't have thylakoid membranes, and the photosynthesis reaction is carried out on cytoplasmic membranes. The reduction of protochlorophyllide (Pchlide) is a key regulatory step in the biosynthesis of chlorophyll in phototrophic organisms. Two distinct enzymes catalyze this reduction; a light-dependent NADPH:Pchlide oxidoreductase (POR) and light-independent Pchlide reductase (DPOR). In this study, we purified POR from G. violaceus using Escherichia coli overexpression system, and determined its kinetic and substrate binding properties. The purified protein is fully active and the activity is light dependent. The evolutionary implication of POR will be discussed based on the comparative analysis of enzymatic properties between G. violaceus POR and those of other cyanobacteria and plant PORs.