Treatments that enhance the latent
ATPase activity of the
chloroplast coupling factor (CF1) also induce
hypersensitivity of the gamma subunit toward
trypsin. A number of different gamma subunit cleavage products are formed (Moroney, J. V., and McCarty, R. E. (1982) J. Biol. Chem. 257, 5910-5914). We have compared the gamma cleavage products of membrane-bound and isolated CF1, activated either by reduction of the gamma
disulfide bond or by removal of the epsilon subunit. The gamma subunit of isolated CF1 lacking the epsilon subunit was cleaved to a 27,000-Da species. The same cleavage site became exposed following energy-dependent conformational changes in the membrane-bound
enzyme. Activation by reduction of the gamma
disulfide bond also exposed this site. However, the gamma subunit of reduced CF1 was cleaved rapidly at an additional site and
trypsin treatment gave rise to a 25,000-Da gamma species. The small
peptide generated by the second cleavage contains one of the cysteinyl residues of the reduced
disulfide bridge of gamma. This
peptide dissociates from the
enzyme and can be isolated by gel filtration. The close proximity of the
trypsin cleavage sites to the
disulfide bond of gamma is discussed with respect to the effects of tryptic cleavage on the
ATPase activity of CF1. The data indicate that structural changes in a limited region of the gamma subunit strongly influence the catalytic properties of both soluble and membrane-bound CF1.