Study of bacteriorhodopsin photocycle with pump-probe method

With pump-probe method, the photocycle of bacteriorhodopsin (BR) was studied in two sets of measuring systems which had different time resolution and exciting mode. The testing beam for the two systems was a 633 nm He-Ne laser. AN avalanche photodiode was used to detect the probing light passing through the sample when pumped by the actinic light. The picked up signal was coupled into a 500MHz digital oscilloscope which measured and processed the BR's photocycle response signal. the experimental results indicate that the period of BR photocycle is less than 15 ms, the time constant from K to L is 2 microsecond, the relaxation time from L to M is 50 microsecond. A doubtable component is found occurring prior to K. Based on the measured data, a model of the BR photocycle in the time domain from nanosecond to millisecond was proposed.