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Actinic Light-Energy Dependence of Proton Release from Bacteriorhodopsin

R. Tóth-Boconádi ^*, S. G. Taneva  and L. Keszthelyi ^*

^* Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary; and Institute of Biophysics, Bulgarian Academy of Sciences, Sofia, Bulgaria

Correspondence: Address reprint requests to L. Keszthelyi, Tel.: 36-62-599615; Fax: 36-62-433133; E-mail: kl{at}nucleus.szbk.u-szeged.hu.

Measuring the light-density (fluence) dependence of proton release from flash excited bacteriorhodopsin with two independent methods we found that the lifetime of proton release increases and the proton pumping activity, defined as a number of protons per number of photocycle, decreases with increasing fluence. An interpretation of these results, based on bending of purple membrane and electrical interaction among the proton release groups of bacteriorhodopsin trimer, is presented.