Some effects of phloridzin and quinacrine on photophosphorylation and carbon dioxide fixation by isolated spinach chloroplasts

A 60–70% inhibition of spinach chloroplast PMS1-catalyzed cyclic photophosphorylation was observed following a 5-min pre-incubation in the dark with either 0.25 mM phloridzin or 10 μM quinacrine. Phloridzin was also shown to severely inhibit the endogenous synthesis of ATP (no catalyst being present). The inhibitors had only a slight effect on the fixation of carbon dioxide. Addition of 3-phosphoglyceric acid was found to inhibit the fixation of CO2 while ribose 5-phosphate stimulated CO2 fixation, even in the presence of 0.25 mM phloridzin.