The amino acid sequence of a factor, 15 kDa protein, which facilitates the formation of, and stabilizes the inactivated complex between mitochondrial ATPase and intrinsic inhibitor was established. The factor was found to be composed of 83 amino acid residues and to have an M r of 9450, though the apparent M r was 15 000 when determiend by SDS—polyacrylamide gel electrophoresis. The factor was characterized as a basic protein with 18 basic and 12 acidic amino acid residues. The amino acid sequence of the factor showed significant homology with those of yeast ATPase inhibitor and the 9 kDa protein which acts in concert with the 15 kDa protein in stabilizing the inactivated ATPase complex.
