The Effect of Buffers on Weak Acid Uptake by Vesicles
The assessment of weak acid membrane permeability ( ) frequently involves large unilamellar vesicles. It relies on measurements of the intravesicular pH drop, ΔpH , in response to a sudden augmentation of external acid concentration. However, ΔpH may be primarily governed by non-instantaneous proton...
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Published in | Biomolecules (Basel, Switzerland) Vol. 9; no. 2; p. 63 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Switzerland
MDPI AG
13.02.2019
MDPI |
Subjects | |
Online Access | Get full text |
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Summary: | The assessment of weak acid membrane permeability (
) frequently involves large unilamellar vesicles. It relies on measurements of the intravesicular pH drop, ΔpH
, in response to a sudden augmentation of external acid concentration. However, ΔpH
may be primarily governed by non-instantaneous protonation and deprotonation reactions of (i) the acid itself, (ii) the buffer molecules, and (iii) the fluorescent pH reporter dye. Moreover, buffer concentration and acid gradient also serve as determinants of ΔpH
, as we show here. The uniexponential time constant (τ) of ΔpH
(t) is an invalid measure of
as Arrhenius plots of
and τ reveal different activation energies for acid influx. We calculate
by fitting a mathematical model to experimental stopped-flow traces. The model takes into account not only the time course of total internal buffer capacity but also (i) water self-dissociation, (ii) volume changes due to acid induced osmotic water flow, and (iii) the spontaneous membrane proton leak. It allows extracting a
of 30.8 ± 3.5 μm/s for formic acid for 1,2-dioleoyl-
-glycero-3-phosphocholine (DOPC) vesicles. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 2218-273X 2218-273X |
DOI: | 10.3390/biom9020063 |