The light intensity dependence of protochlorophyllide photoconversion and its significance to the catalytic mechanism of protochlorophyllide reductase

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Abstract
The light‐dependent step in chlorophyll synthesis by higher plants involves hydrogen transfer from NADPH+to the porphyrin protochlorophyllide catalysed by the photoenzyme protochlorophyllide reductase. The light intensity dependence of the process has been studied in vitro using wheat etioplast membranes. The results suggest that a single photochemical event is involved in the photoconversion. In support of this conclusion we also demonstrate that illumination of these membranes with a train of ultrashort (150 fs) flashes resulted in chlorophyll accumulation. The significance of the findings in terms of possible mechanisms for the reductase are discussed.