Received April 11, 2001; Revision received July 17, 2001
This review deals with the role of carboxylic amino acids in the proton-transport activity of bacteriorhodopsin. The main focus is on the infrared data, which allow direct monitoring of the protonation/deprotonation of specific residues during the proton movement in the course of the photocycle. Additional attention is paid to the potential use of carboxylic acids in proteins as internal sensors, based on the sensitivity of their IR frequencies to the immediate environment.
KEY WORDS: retinal proteins, FTIR, time-resolved, aspartic acid, glutamic acid, COOH stretch, symmetric and antisymmetric stretching vibrations, carbonyl, carboxyl, carboxylate