On the Localization of Organic Acids in Acid-Induced ATP Synthesis

Abstract

This study at the penetration and localization in isolated [spinach] chloroplasts of some selected organic acids under inducing and non-inducing conditions has shown that there are 4 distinct relationships of acid penetration to ATP synthesis. Succinic acid which is effective as an inducer penetrates quite rapidly at pH 4.0 with the time course coinciding with that of acid-poise as determined by ATP synthesis. As the pH of stage I is raised (acid more dissociated) the penetration is slower, and the internal concentration at equilibrium is less. At pH 6.5 where succinic acid is fully dissociated there is little or no penetration of the dianion. A portion of the succinic acid (presumably the dianion) is retained in the chloroplasts on pH transition. This internal acid can be removed by placing plastids back in solution whose pH is less than 5. A relatively ineffective dicarboxylic acid, e.g. malonic, penetrates quite slowly at pH 4.0. The acid-poise is maximized and declines (possibly due to acid dena-turation of phosphorylating enzymes) much before the internal malo-nate is maximal. This dicarboxylic acid also shows little p''enetration as the dianion and some of it is effectively retained on pH transition from 4.0 to 8.4. Acetic, an ineffective acid, penetrates quite well both as the acid and the anion and is not retained as the anion on transition from pH 4.0 to 8.4. Glutamic acid which produces ATP yields comparable to those obtained with HC1 found to penetrate very slowly and did not reveal a measurable amount of retained acid on transition from pH 4.0 to 8.4.