Analysis of substrate specificity of (bacterio)chlorophyll a synthases useing a purple bacterium,Rubrivibax gelatinosus

Abstract

Chlorophyll a and bacteriochlorophyll a biosynthesis pathways are identical except that the latter has two additional steps. The terminal step of these synthesis pathways is esterification with long-chain alcohol. This reaction is catalyzed by ChlG in chlorophyll synthesis and BchG in bacteriochlorophyll synthesis. A recent study, however, suggested that the mutant of cyanobacteria expressing BchF, a specific enzyme in bacteriochlorophyll synthesis, accumulates 3-hydroxyethylchlorophyllide a with a long-chain alcohol. In this study, we constructed mutants lacking bchG and bchXYZ to analyze the substrate specificity of BchG and ChlG in vivo. These mutants accumulated intermediate pigments, metabolites of bacteriochlorophyllide a, chlorophyllide a and 3-hydroxyethylchlorophyllide a, respectively. Results on introduction of chlG of Synechocysts sp.PCC6803 into these mutants will be discussed.