Biogenesis of chloroplast membranes. III. Light-dependent induction of proton pump activity in whole cells and its correlation to cytochrome f photo-oxidation during greening of a Chlamydomonas reinhardti mutant (y-1)

Abstract

A proton pump activity in light-grown whole cells which is sensitive to low concentrations of electron transfer inhibitors and uncouplers is described. Carbonyl cyanide m-chlorophenylhydrazone inhibits the formation of the pH gradient at concentrations which slightly enhance the oxygen evolution in the light. The activity is proportional to chlorophyll concentration, the maximal rate being 1–2 μmoles H + per mg chlorophyll per min. The activity is absent in dark-grown y-1 cells, having only trace amounts of chlorophyll, but present in dark-grown wild-type cells, having a normal chloroplast. During light-induced formation of membranes in the dark-grown y-1 cells, the proton pump activity is completely restored after 2 h of illumination, when only small amounts of chlorophyll have been synthesized. The reactivation of the proton pump during the initial phase of the greening parallels the photoactivation of cytochrome f. Cytochrome f, present in dark-grown y-1 cells, becomes photooxidizable only at about 2 h of greening, before additional cytochrome is synthesized. The activity of Photosystem II (oxygen evolution and ferricyanide reduction) and Photosystem I (cyclic photophosphorylation) could be detected before photoactivation of cytochrome f and proton pump activity. It is concluded that the cytochrome f present in the dark-grown cells is not coupled with the two photo-systems. The coupling or activation occurs within the first 2 h of the greening and is accompanied by the appearance of proton pump activity.