Light-dependent and biochemical properties of two different bands of bacteriorhodopsin isolated on phenyl-sepharose CL-4B

We report a detailed description of the light-dependent and biochemical pro perties of two different bands of isolated and nearly delipidated bacterior hodopsin obtained from chromatography on phenyl-Sepharose CL-4B. The two ba nds (BR I and BR LI) showed a number of markedly different spectroscopic an d biochemical characteristics: different absorption maximums in the dark, d ifferent light/dark adaptations, different M decay kinetics, different stab ilities, different responses to titration with alkali in the dark and diffe rent circular dichroism (CD) spectra, Organic phosphate contents of BR I an d BR II were measured; we found that more than 90% of purple membrane organ ic phosphate was removed in the course of chromatography and that the phosp holipid/protein molar ratio was always higher in BR I than in BR II. In man y functional aspects (high stability, response to light adaptation, spectra l changes in the dark by alkali addition and bilobate CD spectrum) the firs t band appeared to be similar to the purple membrane. We suggest that the f unctional differences between the two bands depend on the fact that the fir st band (BR I) contains mostly bacteriorhodopsin aggregates corresponding t o purple membrane trimers, while the second band (BR II) contains only bact eriorhodopsin monomers.