Measurement of the oxidation-reduction potentials of amicyanin and c-type cytochromes from Paracoccus denitrificans

The oxidation-reduction potentials of four periplasmic electron carrier proteins from Paracoccus denitrificanshave been determined. Their midpoint potentials are: amicyanin, 294±6 mV; cytochrome c-550, 253±5 mV; cytochrome c-551i, 190±4 mV, and cytochrome c-553i, 148±5 mV. Although rapid amicyanin-mediated transfer of electrons from methylamine dehydrogenase to cytochrome c-551i was observed, reduced amicyanin did not reduce oxidized cytochrome c-551i in the absence of methylamine dehydrogenase.