[67] Synthesis and Use of an Azido-Labeled form of the ATPase Inhibitor Peptide of Rat Liver Mitochondria

The binding and dissociation of the mitochondrial ATPase inhibitor peptide by the ATPase complex is governed by the energy state of the inner mitochondrial membrane. To study the interaction of the inhibitor peptide with the ATPase in a quantitative fashion, the chapter describes the synthesis of a radioactive reagent that binds covalently to the inhibitor peptide without affecting its activity. In addition, the same reagent can be used to introduce a covalent cross-link between the inhibitor peptide and its binding site(s) on the ATPase complex. It may not be necessary to have the radioactive marker in the cross-linker itself, such a label has a distinct advantage. It eliminates the need to introduce in a second step the radiolabel. Therefore, the cross-linking radioactive marker may be very useful in the study of protein-protein interactions where the protein of interest is sensitive to chemical reactions or cannot be radioactively labeled otherwise.