Electrochemical analysis of heme functions of myoglobin using semi-artificial myoglobins

To understand the roles of the vinyl groups of heme side chains of protoheme-IX in myoglobin (Mb), we replaced the protoheme-IX in native Mb with mesoheme-IX and deuteroheme-IX, and the bioelectrochemical properties of the substituted Mbs were compared with those of the native Mb. The cathodic peak and the formal potentials of the reconstituted Mbs examined were more negative by ca. 22–90 mV than those of the native Mb. The rates of autooxidation for the oxy-forms of deutero-IX and meso-IX reconstituted Mbs at 35 °C and pH 7.0 were twice as fast than that of the native Mb. These results suggest that the vinyl groups of heme facilitate the reduction of Mbs, and prevent the autooxidation of the heme iron. The dissociation rate of cyanide ion from ferro-Mb was increased in the order of deutero(IX)Mb < meso(IX)Mb < native Mb. On the basis of the electroanalytical studies of the reconstituted Mbs with mesoheme-III, mesoheme-XIII, deuteroheme-III, and deuteroheme-XIII, isomers of type IX, no significant influence of the side chain position of the porphyrin ring on the dissociation property of the cyanide ion was observed. The electron transfer kinetics of the reconstituted Mbs were also evaluated and compared with that of the native Mb. DeuteroMb exhibited a slower electron transfer rate constant than other Mbs.