Chemical Modification and Spin-Label Studies of Carboxyl Residues in Bacteriorhodopsin

摘要

The structural and functional roles of carboxyl residues in bacteriorhodopsin have been investigated by amino acid chemical modification and electron paramagnetic resonance studies of spin-labeled bacteriorhodopsin. Carboxyl modification of bacteriorhodopsin using either the water-soluble reagent, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, or a hydrophobic reagent, N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline, resulted in no changes in the absorption spectra or visible circular dichroism spectra, and the modified protein retained proton pumping activity. A structural role for a carboxyl residue in the bacteriorhodopsin photocycle was found by analyzing the kinetics for the decay of the M sub 412 intermediate. Chemical modification and spin-label studies have identified several distinct functional roles for the buried carboxyl residues of BR in the mechanism of the light-driven proton pump. In addition, these studies obtained structural information which supports current models of BR protein structure in the purple membrane. (ERA citation 08:052305)