Inhibition of Chloroplast Reactions with Phenylmercuric Acetate

Phenylmercuric acetate is a selective inhibitor of the photosynthetic activities of isolated spinach (Spinacia oleracea) chloroplasts. At 5 mum concentration of phenylmercuric acetate, photophosphorylation is inhibited. At 33 mum phenylmercuric acetate, ferredoxin is inactivated. Ferredoxin-NADP oxidoreductase is 50% inhibited at 100 mum phenylmercuric acetate. Photosystem II reactions are 50% inhibited at 150 mum phenylmercuric acetate and very much higher cooncentrations-500 mum-are needed to approach complete inhibition. Phenylmercuric acetate inhibition of photosystem II appears to be selective, blocking a site between the 3-(3,4-dichlorophenyl)-1,1-dimethyl urea sensitive site and the site inactivated by high concentrations of tris buffer.