KINETICS AND MECHANISMS OF PHOTOINDUCED ELECTRON-TRANSFER REACTION OFMAGNESIUM MYOGLOBIN

Horse heart metmyoglobin was reconstituted with magnesium(II) porphyri n, [Mg(dp)] ,18-bis(2-carboxyethyl)porphyrinatomagnesium(II)). Photoin duced electron-transfer (ET) between magnesium myoglobin (MgDPMb) and cationic and anionic quenchers, such as viologens and anthraquinone-2- sulfonate (AQS-), has been studied in an aqueous degassed solution. No ne of the quenchers examined in this work formed a detectable associat ed complex with MgDPMb. The thermal backward ET reaction was observed for these quenchers. Not only photoinduced ET but also thermal backwar d ET reactions were insensitive to the driving force of the reactions. Moreover, there was little effect of metal-ion substitution; the rate of reaction was similar to that for zinc myoglobin. Thus, the reactio ns are controlled by conformational changes in the myoglobins.