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pH dependence of light‐induced proton release by bacteriorhodopsin
Author(s) -
Kono Masahiro,
Misra Saurav,
Ebrey Thomas G.
Publication year - 1993
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(93)80291-2
Subject(s) - bacteriorhodopsin , deprotonation , chemistry , proton , proton transport , ionic strength , halobacterium , tyrosine , ionic bonding , inorganic chemistry , membrane , aqueous solution , ion , biochemistry , organic chemistry , physics , quantum mechanics
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 p K 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 p K a of this group also allows us to calculate the surface charge density of about −5 charges per bacteriorhodopsin, compatible with previous estimates.