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

Abstract

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.

Inhibitor effects on photosynthesis, respiration and active ion transport inHydrodictyon africanum

“…This is consistent with the use in CO2 fixation of some high-energy intermediate on the electron transport side of the site sensitive to phlorizin. Another difficulty is that quinacrine has similar effects to phlorizin on photosynthesis in chloroplasts (Vose & Spencer, 1967), yet the evidence discussed earlier (quinacrine section of Results) suggests that quinacrine-treated chloroplasts cannot make a phosphorylated intermediate of photophosphorylation. However, there are a number of results which are not consistent with this scheme.…”

“…Quinacrine inhibits ATP synthesis in isolated chloroplasts more than it inhibits CO2 fixation (Vose & Spencer, 1967. Quinacrine inhibits ATP synthesis in isolated chloroplasts more than it inhibits CO2 fixation (Vose & Spencer, 1967.…”

“…Alternative (2), the use of some high-energy intermediate of ATP synthesis, rather than ATP itself, in the kinase steps of CO2 fixation, has been suggested by Kylin and Tillberg (1967), Vose and Spencer (1967, and Urbach and Gimmler (1969). Vose and Spencer found that photosynthesis by isolated chloroplasts was relatively insensitive to phlorizin, but that ATP stimulation of photosynthesis was more sensitive to phlorizin.…”

“…Vose and Spencer found that photosynthesis by isolated chloroplasts was relatively insensitive to phlorizin, but that ATP stimulation of photosynthesis was more sensitive to phlorizin. One is the finding by Vose and Spencer (1969) that the ADP stimulation of photosynthesis by chloroplast preparations is at least as phlorizin-sensitive as is the ATP stimulation. This intermediate would presumably be phosphorylated; some evidence for the phlorizin-insensitive formation of such an intermediate has recently been presented by Wu, Myers, and Forrest (1970).…”