Rapid Transfer of Photo-Released Protons from Water to Lipid Membrane

IF 1.1 Q4 CELL BIOLOGY
V. Yu. Tashkin, D. D. Zykova, L. E. Pozdeeva, V. S. Sokolov
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引用次数: 0

Abstract

The transport of protons between the membrane boundary and water can be hindered by the presence of a high potential barrier, which affects their transport across the membrane performed by membrane proteins. To estimate the rate of proton transport across this barrier, photoactivatable compounds whose molecules can adsorb on the membrane boundary and release protons upon excitation are used. We studied such a compound, sodium 2-methoxy-5-nitrophenyl sulfate (MNPS). Its molecule is able to adsorb on a lipid bilayer membrane (BLM) as an anion and release sulfate and proton upon excitation with UV light, becoming an electroneutral product. Upon illumination of the BLM, on one side of which MNPS anions were adsorbed, changes in the electrostatic potential at the membrane-water interface were observed. Slow changes in potential were measured using the intramembrane field compensation method, while fast changes were measured using an electrometric amplifier. When the light was switched on, the potential increased rapidly, and when it was switched off, it slowly returned to its initial value. The rate of rapid potential increase depended on the lipid composition of BLM, buffer concentration, and pH of the medium. The dependence of this rate on pH was different for BLMs formed from phosphatidylcholine and its mixture with phosphatidylserine. With increasing buffer concentration, the rate decreased by a factor of ten. These results indicate that the reaction of proton release during the excitation of MNPS molecules occurs both on the membrane surface and in the water near it. The binding at the membrane of protons released by the reaction of MNPS in water provides the major contribution to the change in electrostatic potential at the membrane boundary, considerably exceeding the contribution of MNPS anions released by the reaction at the membrane.

Abstract Image

光释放质子从水到脂质膜的快速转移
质子在膜边界和水之间的传输可以被高电位屏障的存在所阻碍,这影响了它们通过膜蛋白在膜上的传输。为了估计质子通过该屏障的传输速率,使用了光活化化合物,其分子可以吸附在膜边界上并在激发时释放质子。我们研究了这样一个化合物,2-甲氧基-5-硝基苯基硫酸钠(MNPS)。其分子能够以阴离子形式吸附在脂质双层膜(BLM)上,并在紫外光激发下释放出硫酸盐和质子,成为电中性产物。在BLM的一侧吸附MNPS阴离子后,观察到膜-水界面静电电位的变化。使用膜内场补偿法测量电位的缓慢变化,而使用电计放大器测量快速变化。当开灯时,电势迅速增加,当关灯时,电势慢慢恢复到初始值。快速电位增加的速率取决于BLM的脂质组成、缓冲液浓度和培养基的pH。磷脂酰胆碱及其与磷脂酰丝氨酸的混合物形成的BLMs对pH值的依赖性不同。随着缓冲液浓度的增加,反应速率降低了10倍。这些结果表明,在MNPS分子的激发过程中,质子释放反应既发生在膜表面,也发生在膜附近的水中。MNPS在水中反应释放的质子在膜上的结合对膜边界静电势的变化做出了主要贡献,大大超过了MNPS在膜上反应释放的阴离子的贡献。
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来源期刊
CiteScore
1.40
自引率
0.00%
发文量
28
期刊介绍: Biochemistry (Moscow), Supplement Series A: Membrane and Cell Biology   is an international peer reviewed journal that publishes original articles on physical, chemical, and molecular mechanisms that underlie basic properties of biological membranes and mediate membrane-related cellular functions. The primary topics of the journal are membrane structure, mechanisms of membrane transport, bioenergetics and photobiology, intracellular signaling as well as membrane aspects of cell biology, immunology, and medicine. The journal is multidisciplinary and gives preference to those articles that employ a variety of experimental approaches, basically in biophysics but also in biochemistry, cytology, and molecular biology. The journal publishes articles that strive for unveiling membrane and cellular functions through innovative theoretical models and computer simulations.
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