On the intermolecular electron transfer between different redox states of flavodoxin from Megasphaera elsdenii. A 500-MHz 1H NMR study

Abstract

The electron transfer reactions between molecules of flavodoxin from M. elsdenii in different redox states were investigated by proton NMR techniques at 500 MHz. The electron transfer between molecules in the oxidized and semiquinone state is shown to be at least 350 times slower than that between molecules in the semiquinone and hydroquinone state. The latter reaction was studied at different ionic strengths and temperatures. The rate of electron transfer increases with increasing ionic strength, as expected for a reaction between molecules of identical charges. The electron transfer reaction is only slightly dependent on temperature, suggesting an outer sphere reaction mechanism. The activation energy for the electron transfer reaction between the semiquinone and hydroquinone state is negligible in contrast to that between the oxidized and semiquinone state. This feature may render M. elsdenii flavodoxin to an exclusive 1 electron donor/acceptor in the cell, thereby shuttling between the semiquinone and the hydroquinone state. Mechanistic implications of the findings are briefly discussed.