Biophysical Journal 61: 1630-1637 (1992)
© 1992 the Biophysical Society

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Nanosecond photolytic interruption of bacteriorhodopsin photocycle

K-590 BR-570 reaction

Department of Chemistry and Optical Science Center, University of Arizona, Tucson, Arizona 85721 USA

ABSTRACT

The molecular processes comprising the room temperature bacteriorhodopsin (BR) photocycle are examined through the properties of the photo-induced reverse reaction, K-590 + h BR-570 (K BR). Two sequential pumping pulses, each of 10-ns duration, are used, respectively, to initiate the photocycle via the forward BR-570 + h K-590 (BR K) reaction (532 nm) and to photolytically interrupt the thermal BR photocycle after a 20-ns delay via K BR (620-700 nm). The ground-state BR-570 population, monitored by 633-nm absorption 200 µs after the photocycle begins, provides a quantitative measure of the efficiency with which K BR interrupts the photocycle to reform BR-570. The quantum yield () for K BR is found to be 1.6 ± 0.1 times larger than that for BR K which, when compared to a of 0.64 for BR K, suggests that for K BR is 1.0. The significance of such a high efficiency K BR reaction with respect to mechanistic descriptions of the BR photocycle is discussed.