Chlorophyllide a oxidoreductase Preferentially Catalyzes 8‐Vinyl Reduction over B‐Ring Reduction of 8‐Vinyl Chlorophyllide a in the Late Steps of Bacteriochlorophyll Biosynthesis

Abstract

Bacteriochlorophyll a (BChl) is an essential pigment for anoxygenic photosynthesis. In late steps of the BChl biosynthesis of Rhodobacter capsulatus, the C8 vinyl group and C7=C8 double bond of 8-vinyl chlorophyllide a (8 V-Chlide) are reduced by a C8 vinyl reductase (8VR), BciA, and a nitrogenaselike enzyme, chlorophyllide a oxidoreductase (COR), respectively, to produce 3-vinyl-bacteriochlorphyllide a. Recently, we discovered 8VR activity in COR. However, the kinetic parameters of the COR 8VR activity remain unknown, while those of the COR C7=C8 reductase activity and BciA have been reported. Here, we determined the kinetic parameters of COR 8VR activity by using 8 V-Chlide. The K m value for 8 V-Chlide was 1.4 μM, which is much lower than the 6.2 μM determined for the C7=C8 reduction of Chlide. The kinetic parameters of the dual activities of COR suggest that COR catalyzes the reduction of the C8 vinyl group of 8 V-Chlide preferentially over C7=C8 reduction when both substrates are supplied during BChl biosynthesis.

Distribution and functional analysis of the two types of 8-vinyl reductase involved in chlorophyll biosynthesis in marine cyanobacteria

“…This is the rst study to report enzymatic activity of cyanobacterial BciA. In some photosynthetic bacteria, reduction of the vinyl group at position 8 is achieved by chlorophyllide a oxidoreductase, a distinct enzyme from BciA and BciB (Harada et al 2014;Yamamoto et al 2020), implying great diversity among 8V reductases.…”

Special Issue on Nitrogenases and Homologous Systems

“…Yilin Hu demonstrates how a nitrogenase hybrid containing an unnatural M‐cluster variant can be used to modulate nitrogenase reactivity and provide insights into the mechanism of this enzyme . Gunhild Layer and Jürgen Moser illustrate how chimeric systems comprising components of different members of this enzyme superfamily can help us gain a better understanding of their mechanistic properties, and Yuichi Fujita reports the unexpected reactivity of an enzyme involved in the biosynthesis of bacteriochlorophyll …”