THE LIGHT-INTENSITY DEPENDENCE OF PROTOCHLOROPHYLLIDE PHOTOCONVERSIONAND ITS SIGNIFICANCE TO THE CATALYTIC MECHANISM OF PROTOCHLOROPHYLLIDE REDUCTASE

The light-dependent step in chlorophyll synthesis by higher plants inv olves hydrogen transfer from NADPH(+) to the porphyrin protochlorophyl lide catalysed by the photoenzyme protochlorophyllide reductase. The l ight intensity dependence of the process has been studied in vitro usi ng wheat etioplast membranes. The results suggest that a single photoc hemical event is involved in the photoconversion. In support of this c onclusion we also demonstrate that illumination of these membranes wit h a train of ultrashort (150 fs) flashes resulted in chlorophyll accum ulation. The significance of the findings in terms of possible mechani sms for the reductase are discussed.