THE PHOTOCYCLE OF BACTERIORHODOPSIN AT HIGH PH AND IONIC-STRENGTH .1.EFFECTS OF PH AND BUFFER ON THE ABSORPTION KINETICS

A fitting analysis resolved the kinetics in the microsecond to second time range of the absorption changes in the bacteriorhodopsin photocyc le at pH = 8.0-9.5 in 3 M KCl into seven exponential components, The t ime constants and/or amplitudes of all components are strongly pH-depe ndent. In the pH range studied, the logarithms of the pH-dependent tim e constants varied linearly with pH. The maximum absolute value of the corresponding slopes was 0.4, in contrast with the theoretically expe cted value of 1 for unidirectional reactions coupled directly to proto n exchange with the bulk phase. This indicates that the extracted macr oscopic rate constants are not identical to the microscopic rate const ants for the elementary photocycle reaction steps. Unexpected differen ces were found in the kinetic parameters in CHES and berate buffers.