Abstract
The subunit locations of each of the 3 nucleotide binding sites of soluble [spinach] chloroplast coupling factor 1 were studied with the photoaffinity label 3''-0-(4-benzoyl)benzoyl-ATP. This derivative is an effective inhibitor of ATPase activity. Photolysin of the radioactive label when bound to each of the 3 nucleotide sites on the coupling factor was examined. For the nucleotide site that normally binds ADP very tightly, sodium dodecylsulfate/polyacrylamide gel electrophoresis after photolysis indicates that primarily the .beta. polypeptide chain is appreciably labeled (86%), although some labeling of the .alpha. polypeptide chain is found (14%). For the site that binds MgATP tightly, 97% of the radioactivity is found on the .beta. polypeptide chain. The .alpha. and .beta. polypeptide chains are labeled in approximately equal amounts when photolysis is carried out with the nucleotide analog bound to the 3rd site.