Characterization of chlorophyll a and bacteriochlorophyll a synthases by heterologous expression in Escherichia coli

Genes coding for putative chlorophyll a synthase (chlG) from Synechocystis sp, PCC 6803 and bacteriochlorophyll a synthase (bchG) from Rhodobacter capsulatus were amplified by the polymerase chain reaction and cloned into T7 RNA polymerase-based expression plasmids, In vitro enzymatic assays indicated that heterologous expression of the chlG and bchG gene products in Escherichia coli conferred chlorophyll a and bacteriochlorophyll a synthase activity, respectively, Chlorophyll a synthase utilized chlorophyllide a, but not bacteriochlorophyllide a, as a substrate, whereas bacteriochlorophyll a synthase utilized bacteriochlorophyllide a, but not chlorophyllide a. Both enzymes were also observed to exhibit a marked preference for phytyl diphosphate over geranylgeranyl diphosphate.