The semisynthesis of analogues of cytochrome c. Modifications of arginine residues 38 and 91.

The arginine residues at positions 38 and 91 of horse cytochrome c are absolutely conserved throughout eukaryotic evolution. For studies of the functional roles of these residues, we have prepared, by semisynthetic techniques, analogues of cytochrome c in which one or the other of the arginine residues has been modified. The products of modification by adduct formation with pentane-2,4-dione were purified and extensively characterized. In biological tests, the arginine-91-modified cytochrome c showed little difference in behaviour from native horse cytochrome c. Modification of arginine-38, however, led to extensive changes in biological and chemical properties. We also prepared and tested adducts with cyclohexane-1,2-dione and camphorquinone-10-sulphonic acid. The same effects on biological properties were noted irrespective of the nature of the modifying group. We suggest reasons for the differences in sensitivity of the two sites.