Mechanisms of phototransformation of protochlorophyllide into chlorophyllide.

The purpose of this review is to summarize and discuss data obtained in studies on the mechanisms of the primary photophysical and photochemical reactions of protochlorophyllide photoreduction in plant materials (etiolated leaves and leaf homogenates) and in model systems. Based on the results of numerous studies, it can be stated that the reduction of active forms of the chlorophyll precursor is a multistep process comprising two or three short-lived intermediates characterized by a singlet ESR signal. The first intermediate is probably a complex with charge transfer between protochlorophyllide and the hydride ion donor NADPH. The conserved tyrosine residue Tyr193 of protochlorophyllide oxidoreductase is the donor of the second proton.