Abstract
The kinetics and stoichiometry of light-induced proton release in purple membrane suspensions have been investigated using the pH-indicator dye pyranine and single-turnover flash spectroscopy at a time resolution of 0.1 μs. The number of protons detected by pyranine is inversely proportional to the buffering power of the medium and 1.1 ± 0.2 protons are released per photocycling bacteriorhodopsin molecule (pH 7.0, 20°C). At high ionic strength (250 mM KCl) and higher phosphate buffer concentrations (1 mM) the proton release lags slightly behind the formation of the intermediate M-412 and proton reuptake by the purple membrane parallels the slow decay process of M-412 or the decay of O-640.
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