Photophosphorylation Associated with Photosystem II: I. Photosystem II Cyclic Photophosphorylation Catalyzed by p-Phenylenediamine.
Incubation of spinach chloroplast membranes for 90 minutes in the presence of 50 mm KCN and 100 mum HgCl(2) produces an inhibition of photosystem I activity which is stable to washing and to storage of the chloroplasts at -70 C. Subsequent exposure of these preparations to NH(2)OH and ethylenediaminetetraacetic acid destroys O(2) evolution and flow of electrons from water to oxidized p-phenylenediamine, but two types of phosphorylating cyclic electron flow can still be observed. In the presence of 3-(3,4-dichlorophenyl)-1,1'-dimethylurea, phenazinemethosulfate catalyzes ATP synthesis at a rate 60% that observed in uninhibited chloroplasts. C-Substituted p-phenylenediamines will also support low rates of photosystem I-catalyzed cyclic photophosphorylation, but p-phenylenediamine is completely inactive. When photosystem II is not inhibited, p-phenylenediamine will catalyze ATP synthesis at rates up to 90 mumol/hr.mg chlorophyll. This reaction is unaffected by anaerobiosis, and an action spectrum for ATP synthesis shows a peak at 640 nm. These results are interpreted as evidence for the existence of photosystem II-dependent cyclic photophosphorylation in these chloroplast preparations.
Yocum
C F
CF
Department of Cell and Molecular Biology, Division of Biological Sciences, The University of Michigan, Ann Arbor, Michigan 48109.
Guikema
J A
JA