The novel nonlinear optical method second harmonic generation-circular dichroism (SHG-CD) has been used to follow the adsorption and redox properties of a peripheral membrane protein horse heart cytochrome c, adsorbed at several model membrane surfaces. SHG-CD response is shown to be effected by the oxidation state of the heme within surface-adsorbed cytochrome c, as is consistent with the sensitivity of SHG to the chirality of the heme. SHG-CD measurements show that adsorbed cytochrome c is reducible by ascorbate at alkanethiol surfaces, but not at a phospholipid/alkanethiol hybrid bilayer membranes (HBMs). The adsorption of cytochrome c at the model membrane surfaces was verified by surface plasmon resonance. Surface enhanced resonance Raman measurements show that cytochrome c adsorbed on a hybrid bilayer membrane retains the Fe-heme conformation associated with solution-phase cytochrome c and is reducible by applying potential to the supporting electrode. The inability of ascorbic acid to reduce cytochrome c associated with the HBM is attributed not to a change in its redox potential, but rather to the nature of the interaction of cytochrome c with the HBM.
Pub Type: Journals
cytochrome c, hybrid bilayer membrane, nonlinear optics, second harmonic generation, surface enhanced resonance Raman