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. 1978 Sep;23(3):375–382. doi: 10.1016/S0006-3495(78)85456-3

Primary intermediates in the photochemical cycle of bacteriorhodopsin.

M L Applebury, K S Peters, P M Rentzepis
PMCID: PMC1473525  PMID: 698342

Abstract

Picosecond studies of the primary photochemical events in the light-adapted bacteriorhodopsin, bR570, indicate that the first metastable intermediate K610 is formed with a rise time of 11 ps. Difference spectra obtained at 50 ps after excitation show that K610 is the same species as that trapped in low temperature glasses. A precursor species (S) of the K610 intermediate has been observed which is red shifted with respect to K610 and is formed within the 6-ps time width of the excitation pulse. The formation of the precursor has no observable thermal dependence between 298 degrees and 1.8 degrees K. The formation of K610 has a very low thermal barrier and at very low temperatures, the rate of formation becomes practically temperature independent which is characteristic of a tunneling process. The rate of formation becomes practically temperature independent which is characteristic of a tunneling process. The rate of formation of K610 has a moderate deuterium isotope effect of kH/kD approximately 1.6 at 298 degrees K and 2.4 at 4 degrees K. The mechanism for formation of K610 is found to involve a rate-limiting proton transfer which occurs by tunneling at low temperatures.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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