A POSSIBLE PROTEIN MOTION DURING THE BACTERIORHODOPSIN PHOTOCYCLE DETECTED BY COMBINED PHOTOTHERMAL BEAM DEFLECTION AND OPTICAL-DETECTION

Photothermal beam deflection of bacteriorhodopsin in the time range from 1 to 200 mus resolved a new process with a time constant of approx. 20 mus at 20-degrees-C in addition to the K and L decays with time constants of 1.3 and 90 mus. The latter time constants are concordant with those obtained by nanosecond flash photolysis with optical detection on the same samples. The additional process may be ascribed to a protein conformational change during the decay of L --> M, i.e., concomitant with the starting of the proton transfer.