Abstract
Protochlorophyllide (Pchlide) reduction in chlorophyll biosynthesis is catalyzed by two structurally unrelated enzymes; dark-operative Pchlide oxidoreductase (DPOR) and light-dependent Pchlide oxidoreductase (LPOR). It is suggested that DPOR is the older enzyme, and LPOR evolved after oxygenic photosynthesis had been established. Molecular phylogenetic analyses suggest that Gloeobacter violaceus PCC 7421 is the earliest diverged cyanobacterium, which is supported by some unique characteristics such as lack of thylakoids and very low content of chlorophyll. G. violaceus may have primitive features of chlorophyll biosynthetic pathway. Here we report enzymatic properties of LPOR from G. violaceus. The LPOR gene glr2486 was expressed in E. coli and Glr2486 protein was purified. Glr2486 showed Pchlide reduction activity dependent on light and NADPH. Km for Pchlide was 0.7 μM, which was the lowest value in the known cyanobacterial LPORs. This result suggests that LPOR of G. violaceus is an efficient enzyme in terms of affinity for Pchlide.
