A simple method for the determination of reduction potentials in heme proteins

We describe a simple method for the determination of heme protein reduction potentials. We use the method to determine the reduction potentials for the PAS-A domains of the regulatory heme proteins human NPAS2 (E[subscript m] = ˗115 mV ± 2 mV, pH 7.0) and human CLOCK (E[subscript m] = ˗111 mV ± 2 mV, pH 7.0). We suggest that the method can be easily and routinely applied to the determination of reduction potentials across the family of heme proteins.