Redox Reactions in the Last Steps of Chlorophyll Biosynthesis

Abstract

The last steps of chlorophyll biosynthesis are formation of chlorophyllide a ( Chlide a) from protochlorophyllide a (Pchlide a), esterification to chlorophyll a (Chl a) and formation of Chl b. Redox reactions are the reduction of ring D (Pchlide →Chlide), the oxidation of the methyl group at C-7 to a formyl group (Chl a→ Chl b), and the reverse reaction, reduction of the formyl group at C-7 to a methyl group (Chl b →Chl a). We investigated these redox reactions either with the enzymes that were (partially) purified from oat and barley etioplasts or with recombinant enzymes overexpressed in E. coli. Reduction of ring D, catalyzed by NADPH: protochlorophyllide oxidoreductase (POR), requires light. Several modified Pchlide derivatives were applied. The results allow a tentative model for the enzyme mechanism. The oxidation of Chl a derivatives to Chl b compounds with the recombinant chlorophyll a oxidase will be described here for the first time. The in vitro reaction will allow to investigate the requirement for cofactors.