Redox potentials of the cytochromes in the respiratory chain of aerobically grown Escherichia coli

Abstract

The midpoint oxidation-reduction potentials of the cytochromes of the respiratory chain of Escherichia coli were determined. Cytochromes d and a 1 had midpoint oxidation-reduction potentials of +260 and +147 mV, respectively. Cytochrome b was resolved into two major components, cytochrome b 558 and cytochrome b 556, by difference spectroscopy at 77 °K and by potentiometric titrations. These cytochromes had midpoint oxidation-reduction potentials of +165 and +35 mV, respectively, in membranes from exponential-phase cells. The amount of the high and low potential forms of cytochrome b varied with the growth phase.