The Polypeptide Compositions of Bovine Cytochrome Oxidase and Its “ Proteinase-treated” Derivative

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Abstract
An ordinary preparation of bovine cytochrome oxidase [EC 1.9.3.1] at a purity of around lOnmoles heme a per mg protein was resolved into six polypeptide components of 40,000, 25,000, 19,000, 14,000, 10,000 and 8,000 daltons by SDS* polyacryl-amide gel electrophoresis, although the last component appeared to be heterogeneous, involving even smaller fragments. On the other hand, when “ proteinase-treated cytochrome oxidase,” which was derived from the ordinary preparation by limited proteolysis and retained the same enzymic activity as the starting material, was subjected to SDS gel electrophoresis, only two major components of 14,000 and 11,000 daltons were observed. Therefore, it is possible that these two polypeptides are functionally essential. However, from a comparison of their amino acid compositions, the 11,000-dalton component is suggested to have been derived from the 14,000-dalton component by partial proteolysis. Based on these findings, a model of cytochrome oxidase is presented.

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