Isolation and amino acid sequence of the smallest subunit of beef heart bc₁ complex

The 11 subunits of beef heart bc1 complex can be separated either by a new SDS-PAGE system or by a series of chromatographic steps involving dissociation of the complex by salt treatment. The amino acid sequence of the smallest subunit was determined by complete solid-phase Edman degradation and was confirmed by sequencing the N-terminal part and the C-terminal tryptic fragment by liquid-phase Edman degradation. The protein consists of 56 amino acid residues; the Mr was calculated to be 6363. The protein ('ISP binding factor') might be entangled in the reassembly of the iron-sulfur protein with the bc1 subcomplex.