Interaction between .delta. and .epsilon. subunits of F1-ATPase from pig heart mitochondria. Circular dichroism and intrinsic fluorescence of purified and reconstituted .delta..epsilon. complex

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Abstract
A .delta..epsilon. complex has been purified as a molecular entity from pig heart mitochondrial F1-ATPase. This .delta..epsilon. complex has also been reconstituted from purified .delta. and .epsilon. subunits. Both isolated and reconstituted .epsilon. complexes have .delta.1.epsilon.1 stoichiometry and are indistinguishable by their chromatographic behavior, their circular dichroism spectra (CD spectra), and their intrinsic fluorescence features. The content of secondary structures deduced from CD spectra of the .delta..epsilon. complex appears to be the sum of the respective contributions of purified .delta. and .epsilon. subunits. All intrinsic fluorescence studies carried out on isolated .epsilon. subunit and .delta..epsilon. complex show that the single tryptophan residue located on .epsilon. is involved in the interaction between .delta. and .epsilon. subunits. Results obtained with F1-ATPase are in favor of the same .delta..epsilon. interaction in the entire enzyme.