ABSTRACT
Rhodopsin (Rh), the visual pigment of vertebrates, and the purple pigment of Halobac-terium halobium have retinal chromophores bound to apoproteins through Schiff base linkages. The differences in the structures of the visual opsins also enable them to bind to the same 11-cis-retinal and yet yield pigments of widely varying absorption maxima. Rhs are exquisitely sensitive photon detectors while bacteriorhodopsin provides the hypoxic cell with an alternate source of energy, namely adenosine triphosphate generated by a proton gradient across the bacterial cell membrane. The purpose of synthesizing retinal analogs in which the 11,12-double bond is part of a ring was to create rhodopsins that would allow evaluation of the 11-cis to 11 -trans isomerization in the bleaching of natural rhodopsins. Detailed studies were carried out to determine at which stage the bleaching sequence of bovine rhodopsin was inhibited by the seven-membered ring-containing chromophore in bovine Rh7 rhodopsin.
