Polarographic study of bacteriorhodopsin

Abstract Bacteriorhodopsin, the protein-retinal complex from Halobacterium halobrium , shows the polarographic reversible reduction wave at −1.0 V ( vs . n.c.e.) in aqueous solution on the d.m.e. The half-wave potential is independent of pH and therefore protons are not involved in the electrodic process itself.The wave amplitude increases linearly with the growth of bacteriorhodopsin concentration up to 10 −5 M , then adsorption restrictions dominate. The anodic peak of bacteriorhodopsin oxidation at about +0.6 V was obtained. The difference U ox - U red 1 2 is V and is close to the energy of fluorescence quantum of bacteriorhodopsin. This confirms that the chromophore part of bacteriorhodopsin is responsible for the redox reactions observed. The ability of bacteriorhodopsin to be subjected to reversible redox reactions and the fact that its molecule can store energy of about 1.6 eV make this molecule very similar to chlorophyll. The suggestion arises that photosensitized electron transfer might play a role in the functioning of the purple membranes.