The chloroplast ATP synthase: A rotary enzyme?

The chloroplast adenosine triphosphate (ATP) synthase is located in the thy lakoid membrane and synthesizes ATP from adenosine diphosphate and inorgani c phosphate at the expense of the electrochemical proton gradient formed by light-dependent electron flow. The structure, activities, and mechanism of the chloroplast ATP synthase are discussed. Emphasis is given to the inher ent structural asymmetry of the ATP synthase and to the implication of this asymmetry to the mechanism of ATP synthesis and hydrolysis. A critical eva luation of the evidence in support of and against the notion that one part of the enzyme rotates with respect to other parts during catalytic turnover is presented. It is concluded that although rotation can occur, whether it is required for activity of the ATP synthase has not been established uneq uivocally.