Effect of iodination on the pK of Schiff base deprotonation and M412 production in purple membrane |
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Authors: | G. Gogel Aaron Lewis |
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Affiliation: | 1. Department of Chemistry, Colgate University, Hamilton, New York 13346 USA;2. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853 USA |
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Abstract: | Previously, kinetic resonance Raman measurements as a function of pH have been used to demonstrate that, microseconds after light absorption, the pK of Schiff base deprotonation during the bacteriorhodopsin photocycle is 10.2 ± 0.3, whereas before the light event, the pK is > 12 (2). In this investigation, we have iodinated purple membrane suspensions and have found that the pK of Schiff base deprotonation in the photocycle has been lowered to between 7 and 8 for iodinated bacteriorhodopsin. These results, together with our previous data on the pK of Schiff base deprotonation, suggest that the amino acid tyrosine could be a critical component in the deprotonation mechanism. |
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