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.