ATP formation caused by acid-base transition of spinach chloroplasts.

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Abstract
Chloroplasts form a limited amount of ATP without illumination or oxygen if made first acid, then basic. The yields are greatly increased by having an appropriate organic acid present in the acid stage. Lack of specificity of the acid suggests it does not serve as a substrate for a specific enzyme. The highest yields obtained regularly have been 1 ATP for every 4 chlorophylls (i.e. 100 ATP/cytochrome f, or 40 [mu]moles ATP/g of protein). Formation of ATP is sensitive to known uncouplers of photo synthetic phosphorylation, and the kinetics of either decay of the intermediate or of phosphorylation at pH 8 are the same as those for the high-energy condition induced by illumination at pH 6. The yield of ATP depends in part on the actual pH differential between the 2 experimental stages. The data are suggested to be consistent with a model in which the high-energy condition consists of a pH gradient across the grana disk membranes.