Evidence for solvent-induced conformational changes of the soluble Dunaliella chloroplast coupling factor 1 (CF1)

The ATPase activity of the chloroplast coupling factor 1 (CF₁) isolated from the green alga Dunaliella is completely latent. A brief heat treatment irreversibly induces a Ca²⁺ -dependent activity. The Ca²⁺ dependent ATPase activity can be reversibly inhibited by ethanol, which changes the divalent cation dependency from Ca²⁺ to Mg²⁺. Both the Ca²⁺ -dependent and Mg²⁺ -dependent ATPase activities of heat-treated Dunaliella CF₁ are inhibited by monospecific antisera directed against Chlamydomonas reinhardi CF₁. However, when assayed under identical conditions, the Ca²⁺ -dependent ATPase activity is significantly more sensitive to inhibition by the antisera than is the Mg²⁺ -dependent activity. These data are interpreted as indicating that soluble Dunaliella CF₁ can exist in a variety of conformations, at least one of which catalyzes a Ca²⁺ -dependent ATPase and two or more of which catalyze an Mg²⁺ -dependent ATPase.