The succinic oxidase segment of heart mitochondria involves the succinic dehydrogenase-containing complex II, the cytochrome bc1-containing complex III and cytochrome c oxidase or complex IV. We have obtained preliminary models of the structure of these three electron transfer complexes by a combination of physical and chemical approaches. We propose to elaborate on these models through a variety of different experiments aimed at more specifically localizing subunits and prosthetic groups in each complex. Labelling studies with arylazidophospholipids are planned. Such studies will reveal which subunits of this complex are within the lipid bilayer. Antibodies will be raised against each subunit of complex III in order to further delineate the arrangement of these components between the matrix and cytoplasmic sides of the mitochondrial inner membrane. Labelling studies with (35S) diazobenzenesulfonate, (35S) N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate and arylazidophospholipids will be used to map the folding of individual subunits within the cytochrome c oxidase complex. The binding site of interaction of cytochrome c will be localized on the cytochrome c oxidase complex. The interaction of cytochrome c with complex III will be examined and the binding site for this cytochrome with cytochrome c peroxidase and cytochrome b5 will be explored. Additionally, experiments are planned to determine the subunit(s) of cytochrome c oxidase involved in the proton pumping activity of this enzyme.