Use of specific lysine modifications to locate the reaction site of cytochrome c with cytochrome oxidase

Abstract

The reaction of [horse heart] cytochrome c with trifluoromethylphenyl isocyanate was carried out under conditions which led to the modification of a small number of the 19 lysines. Extensive ion-exchange chromatography was used to separate and purify 6 different derivatives, each modified at a single lysine residue, lysines 8, 13, 27, 72, 79 and 100, respectively. The only modifications which affected the activity of cytochrome c with cytochrome oxidase (EC 1.9.3.1) were those of lysines immediately surrounding the heme crevice, lysines 13, 27, 72 and 79, and also lysine 8 at the top of the heme crevice. The modified cytochrome c had the same Vmax as that of native cytochrome c, but an increased Km for the high affinity phase of the reaction. This supports the hypothesis that the cytochrome oxidase reaction site is located in the heme crevice region, and the highly conserved lysine residues surrounding the heme crevice are important in the binding.