Evidence for the Presence of Protochlorophyllase in Etiolated Wheat Seedlings

The biosynthetic pathway to chlorophyll a (chl a) is now quite complete in terms of porphyrin intermediates (3, 8). The biosynthetic pathway to protochlorophyll a (Pchl a) is undoubtedly identical with that of chl a to the protochlorophyllide a (Pchlide a) step, however, the sequence of steps from Pchlide a to Pchl a still remains unknown (1, 9). The production of Pchl a by etiolated plants (devoid of chl a and b) can be explained most simply as an oxidation of chl a (9) or a phytylation of Pchlide a (1,9) by an esterase enzyme (e.g. protochlorophyllase). As the formation of chlorophyllide a (chlide a) requires light, the former pathway seems unlikely in etiolated plants, and the latter becomes the simplest hypothesis, namely, that an esterase catalyzes the formation of Pchl a from Pchlide a.