The Reduction of Protochlorophyllide into Chlorophyllide

The action of light on the protochlorophyllide-protein complex was studied intact, etiolated leaves using low-temperature spectrofluorometry and short-time illuminations (less than 1 s to 1 ms). The first spectral changes observed were shown to correspond to the photoproduction within very short times of a particular pigment form, different from the chlorophyllide-lipoprotein complex, which was called P688-676. The kinetics of these changes was found to be of the first order when 647 nm photons (or photons of longer wavelengths) were used; it was not of the first order when 630 nm photons (or photons of shorter wavelengths) were used. A plausible preliminary model involving two kinds of lipoprotein-protochlorophyllide complexes, one of which receives light energy from an accessory pigment, is proposed to account for the experimental facts.