Novel bacteriorhodopsin analogues based on azo chromophores

Abstract

Bacteriorhodopsin analogues BR-I, BR-II and BR-III containing azo chromophores 4-[[4'-(N,N-dimethylamino)phenyl-1']azo]benzaldehyde, 3-[4-[[4'-(N,N-dimethylamino)phenyl-1']azo]phenyl-1]prop-2-enal and 3-[4-[[4'-(N,N-dimethylamino)phenyl-1']azo]phenyl-1]-2-methylprop-2-enal, respectively, were prepared and characterized by UV-vis spectroscopy, opsin shift, competitive binding with retinal, fluorescence spectroscopy, light-induced pH change, and flash photolysis. BR-I, BR-II, and BR-III had UV-vis absorption maxima at 458, 597, and 485 nm and opsin shifts of −329, 3091, and 43 cm⁻¹, respectively. Competitive binding studies showed that the azo chromophores could not be easily displaced by retinal. Quenching of protein fluorescence by the azo chromophores indicated intimate interactions occurring between the respective azo chromophores and the protein bound residues. The proteins were also found to show functional characteristics (light-induced pH change and flash photolysis profiles) different from those of native bacteriorhodopsin. The results are discussed in terms of the nature of interaction between the azo chromophore and the surrounding protein.