The artificial pigment of bacteriorhodopsin was synthesized from aii-fra/u-naphthylretinal [(all-E)-3-methyl-7-(2-naphthyl)-2,4,6-octatrienal] and bacterioopsin in membranes. Two kinds of pigments were formed with all-fra/iy-naphthylretinal; one has its absorption maximum at 503 nm (Np-bR503) and another, at 442 nm (Np-bR.442). When the retinal/protein ratio on mixing is smaller, the larger amount of Np-bR503 is formed. The equimolar mixture produces Np-bR442. Successive addition of small amounts of naphthylretinal yields almost 100% of Np-bR503. The all-trans isomer of naphthylretinal was extracted from both pigments. After reduction of the pigments with sodium borohydride, addition of all-trans-retinal did not produce bacteriorhodopsin. This indicates that the binding site of naphthylretinal in both pigments is the same as that of trans-bR. But the CD spectra of both pigments were different from each other; that of Np-bR503 represents characteristic exciton CD bands, while that of Np-bR442 shows only a positive one. When incorporated into lipid vesicles, both pigments showed a light-dependent proton pumping activity.
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