Studies on the System Regulating Proton Movement across the Chloroplast Envelope

Studies were undertaken to further characterize the spinach (Spinacea oleracea) chloroplast envelope system, which facilitates H(+) movement into and out of the stroma, and, hence, modulates photosynthetic activity by regulating stromal pH. It was demonstrated that high envelope-bound Mg(2+) causes stromal acidification and photosynthetic inhibition. High envelope-bound Mg(2+) was also found to necessitate the activity of a digitoxinand oligomycin-sensitive ATPase for the maintenance of high stromal pH and photosynthesis in the illuminated chloroplast. In chloroplasts that had high envelope Mg(2+) and inhibited envelope ATPase activity, 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide was found to raise stromal pH and stimulate photosynthesis. 2-(Diethylamino)-N-(2,6-dimethylphenyl)acetamide is an amine anesthetic that is known to act as a monovalent cation channel blocker in mammalian systems. We postulate that the system regulating cation and H(+) fluxes across the plastid envelope includes a monovalent cation channel in the envelope, some degree of (envelope-bound Mg(2+) modulated) H(+) flux linked to monovalent cation antiport, and ATPase-dependent H(+) efflux.