Semisynthesis ofhorse heart cytochrome canalogues fromtwoor three fragments

Horseheart cytochrome cwascleaved with cyanogen bromide. Thelargest fragment, (Hse65)cytochrome c-(1-65)-pentahexacontapeptide lactone, wasusedinconden- sations involving fouranalogues ofthecomplementary cytochrome c-(66-104)-nonatriacontapeptide. Twoofthelatter compounds wereobtained fromasemisynthesis starting with a partially protected fragment NE8&-N^100.penta(methylsulfo- nylethyloxycarbonyl)cytochrome c-(81-104)-tetracosapeptide (also arising fromacyanogen bromide-mediated degradation) andanalogues ofthemiddle part, cytochrome c-(66-80)- pentadecapeptide, which wereprepared byorganochemical synthesis. Twoother analogues ofthecytochrome c-(66-104)- nonatriacontapeptide wereprepared entirely byorganochemi- calsynthesis. Eachofthecovalently recombined analogous cytochromes ccouldretain anelectron inthepresence of oxygen andtransfer ittocytochrome coxidase, although with different reaction rates andMichaelis constants. Their redox potentials varied overabroad range. Theexchanges Tyr67 -* Phe(F) andThr78 -> Valgaverise toanalogues with alower redox potential thannative cytochrome c,while theexchange Phe82-* LeuorTyr97- Leuledtoanalogues with thesameand ahigher redoxpotential, respectively.