Protochlorophyllide reductase. III: Synthesis of a protochlorophyllide-dihydroflavin complex

A mild and efficient method of linking a dihydroflavin to the C-17 carboyxlic acid side chain of protochlorophyllide, without degradation of the sensitive E ring or loss of magnesium, is described. The appended dihydroflavin was shown to quench the fluorescence of protochlorophyllide. In contrast, a dihydronicotinamide moiety was unable to effect fluorescence quenching. the relevance of these findings to a possible mechanism of action of the enzyme protochlorophyllide reductase is discussed.