Isolation and amino acid sequence of the 8 kDa DCCD-binding protein of beef heart ubiquinol:cytochrome c reductase.

The 8 kDa protein of beef heart ubiquinol:cytochrome c reductase was detected by means of a new SDS-PAGE [(1985) FEBS Lett. 190, 89-94] system and was isolated by a series of chromatographic steps involving dissociation of the complex by salt treatment. The amino acid sequence was determined by solid-phase Edman degradation of both the N-terminal part of the whole protein and proteolytic cleavage fragments of the protein. The protein consists of 78 amino acid residues: its Mr was calculated to be 7998. Structure predictions have been made from average and sided hydropathy profiles. The suggested structure encompasses an alpha-helix and a beta-strand, the latter comprising a glutamic acid residue situated in a relatively hydrophobic neighbourhood. This residue may be responsible for the fact that the 8 kDa protein is the first subunit of the whole reductase (consisting of 11 subunits) to be labelled by DCCD when the reductase is in free form or inlaid in phospholipid vesicles.