Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry
- 1 December 1988
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 85 (24) , 9509-9513
- https://doi.org/10.1073/pnas.85.24.9509
Abstract
The question of the basic functional transport unit of bacteriorhodopsin (BR) has been addressed by comparing the proton pumping stoichiometry as well as the photocycle kinetics of monomeric and aggregated BR in phosholipid vesicles. When time-resolved laser spectroscopy was used in combination with the optical pH-indicator pyranine, single-turnover experiments revealed approximately 0.5-0.8 and 0.8-1.2 protons vectorially translocated per photocycling monomeric and aggregated BR molecule, respectively. Since both these values are akin and very similar to the pumping stoichiometry of crystalline BR molecules in the purple membrane, the BR monomer has been proven to be the essential transport unit. The natural arrangement of the photopigments in a crystalline array of immobilized trimers is not required for efficient vectorial proton translocation.Keywords
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