pH dependence of light‐induced proton release by bacteriorhodopsin
Open Access
- 27 September 1993
- journal article
- research article
- Published by Wiley in FEBS Letters
- Vol. 331 (1-2) , 31-34
- https://doi.org/10.1016/0014-5793(93)80291-2
Abstract
We have measured the current generated by light‐activated proton release from bacteriorhodopsin into solution as a function of both pH and ionic strength. We find that proton release into solution decreases with increasing pH with an intrinsic pK a of 8.2 ± 0.2. This pH dependence indicates that the deprotonation of a certain group inhibits or abolishes proton release. Under physiological conditions, this group either releases a proton directly into solution or interacts with the site of proton release. The most immediate candidates for this protonatable species are tyrosine‐57, tyrosine‐185, arginine‐82, and water; acting individually or cooperatively. The salt dependence of the apparent pK a of this group also allows us to calculate the surface charge density of about −5 charges per bacteriorhodopsin, compatible with previous estimates.Keywords
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