Studies were conducted on: photophosphorylation; coupling factor ATPase activities; coupling factor subunit structure; chloroplast membranes; isolation and characterization of coupling factor; a photon counting system for measurement of very short fluorescence lifetimes; phosphorylation coupling factor from chloroplasts labelled with 5-iodo-acetamidofluorescein; and pH and substrate induced conformational changes in chloroplast coupling factor. (HLW)