Exploration of δ‐subunit interactions in beef heart mitochondrial F1 ‐ATPase by monoclonal antibodies

Abstract
Three monoclonal antibodies (mAbs) recognizing distinct epitopes on the δ‐subunit of beef heart mitochondrial F1‐ATPase were studied for their reactivity towards the δ‐subunit both in isolated F1 and in the F0‐F1 complex of submitochondrial particles. Two of the antibodies termed mAb δ 195 and mAb δ239 had free access to δ in F1 and the F0‐F1 complex. Partial hindrance was observed for the third antibody mAb δ22. By a double antibinding assay, it was found that the binding sites for mAb δ195 and mAb δ239 were close to each other and possibly overlapping. Mapping studies conducted with the isolated δ‐subunit showed that mAb δ195 and mAb δ239 interacted with the N‐terminal portion of δ extending from Ala‐1 to Met‐16, whereas mAb δ22 interacted with the fragment spanning Ser‐17‐Glu‐68. It was concluded that the Ala‐1‐Met‐16 segment of the δ‐subunit in F1 and the F0‐F1 complex is freely accessible from the outside, whereas the Ser‐17‐Glu‐68 segment of δ is partially hidden, possibly as a result of interactions with other subunits.

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