THE CHLOROPLAST ATP SYNTHASE - STRUCTURAL-CHANGES DURING CATALYSIS

This article summarizes some of the evidence for the existence of ligh t-driven structural changes in the epsilon and gamma subunits of the c hlorplast ATP synthlse: Formation of a transmembrane proton gradient r esults in: (1) a change in the position of the epsilon subunit such th at it becomes exposed to polyclonal antibodies and to reagents which s electively modify epsilon Lys109; (2) enhanced solvent accessibility o f several sulfhydryl residues on the gamma subunit; and (3) release/ex change df tightly bound ADP from the enzyme. These and related experim ental observations can, at least partially, be explained in terms of t wo different bound conformational states of the epsilon subunit. Evide nce for structural changes in the enzyme which are driven by light or nucleotide binding is discussed with special reference to the popular rotational model for catalysis.