KINETICS AND MECHANISMS OF PHOTOINDUCED ELECTRON-TRANSFER REACTION OF MAGNESIUM MYOGLOBIN

Horse heart metmyoglobin was reconstituted with magnesium(II) porphyrin, [Mg(dp)] (3,7,12,17-tetramethyl-2,18-bis(2-carboxyethyl)porphyrinatomagnesium(II)). Photoinduced 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. None of the quenchers examined in this work formed a detectable associated complex with MgDPMb. The thermal backward ET reaction was observed for these quenchers. Not only photoinduced ET but also thermal backward 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 reactions are controlled by conformational changes in the myoglobins.