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. 1992 Jul 1;89(13):5996–6000. doi: 10.1073/pnas.89.13.5996

Surface-bound optical probes monitor protein translocation and surface potential changes during the bacteriorhodopsin photocycle.

J Heberle 1, N A Dencher 1
PMCID: PMC402125  PMID: 1497755

Abstract

Light-induced H+ release and reuptake as well as surface potential changes inherent in the bacterio-rhodopsin reaction cycle were measured between 10 degrees C and 50 degrees C. Signals of optical pH indicators covalently bound to Lys-129 at the extracellular surface of bacteriorhodopsin were compared with absorbance changes of probes residing in the aqueous bulk phase. Only surface-bound indicators monitor the kinetics of H+ ejection from bacteriorhodopsin and allow the correlation of the photocycle with the pumping cycle. During the L550----M412 transition the H+ appears at the extracellular surface of bacteriorhodopsin. Surface potential changes detected by bound fluorescein or by the potentiometric probe 4-[2-(di-n-butylamino)-6-naphthyl]vinyl-1-(3-sulfopropyl)pyridinium betaine (di-4-ANEPPS) occur in milliseconds concomitantly with the formation and decay of the N intermediate. pH indicators residing in the aqueous bulk phase reflect the transfer of H+ from the membrane surface into the bulk but do not probe the early events of H+ pumping. The observed retardation of H+ at the membrane surface for several hundred microseconds is of relevance for energy conversion of biological membranes powered by electrochemical H+ gradients.

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Selected References

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