The membrane's purple color comes from a bacteriorhodopsin component called retinal, which is strongly bound to an amino acid inside the membrane channel.
That behavior has prompted research on the use of bacteriorhodopsin as the light-sensitive element in artificial retinas and as memory or processing units in protein-based or optical computers (SN: 3/8/97, p.
A thin film of bacteriorhodopsin can also change its color in response to an external electric field.
Like ink on paper, images on a bacteriorhodopsin display are visible in ambient light.
Several groups have used bacteriorhodopsin as computer memory and as the light-sensitive element in artificial retinas.
Aaron Lewis and his colleagues at the Hebrew University of Jerusalem impregnated a plastic film with equal concentrations of the purple and yellow forms of bacteriorhodopsin.
That varying intensity altered the relative concentrations of the purple and yellow forms of bacteriorhodopsin.