Redox reactions in the last steps of chlorophyll biosynthesis

The last steps of chlorophyll biosynthesis are formation of chlorophyllide a ( Chlide a) from protochlorophyllide a (Pchlide a), esterification to chl orophyll a (Chl a) and formation of Chi b. Redox reactions are the reductio n of ring D (Pchlide --> Chlide), the oxidation of the methyl group at C-7 to a formyl group (Chl a--> Chi 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) purifi ed from oat and barley etioplasts or with recombinant enzymes overexpressed in E. coli. Reduction of ring D, catalyzed by NADPH: protochlorophyllide o xidoreductase (POR), requires light. Several modified Pchlide derivatives w ere applied. The results allow a tentative model for the enzyme mechanism. The oxidation of Chi a derivatives to Chi b compounds with the recombinant chlorophyll a oxidase will be described here for the first time. The in vit ro reaction will allow to investigate the requirement for cofactors.