Evidence from simultaneous intracellular- and surface-pH transients that carbonic anhydrase II enhances CO2 fluxes across Xenopus oocyte plasma membranes.
Evidence from simultaneous intracellular- and surface-pH transients that carbonic anhydrase II enhances CO2 fluxes across Xenopus oocyte plasma membranes.
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来自同时发生的细胞内和表面 pH 瞬变的证据表明，碳酸酐酶 II 可以增强跨非洲爪蟾卵母细胞质膜的 CO2 通量。
DOI：
10.1152/ajpcell.00051.2014
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
Boron,WalterF
中科院分区：
文献类型：
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作者：
Musa-Aziz,Raif;Occhipinti,Rossana;Boron,WalterF
α-碳酸酐酶（英语：α-carbonic anhydrase，CA）是一种含锌的酶，催化CO2和HCO 3 −的相互转化。在这里，我们专注于人类CA II（CA II），一种普遍存在的细胞质酶。在本系列的第二篇论文中，我们研究了细胞外表面的CA IV。将重组CA II在Tris溶液（或仅Tris）中显微注射到卵母细胞中后，我们将卵母细胞暴露于1.5%CO2/10 mM HCO 3 −/pH 7.50，同时使用微电极监测细胞内pH值（pHi）和表面pH值（pHS）。CO2内流引起常见的持续pHfall和瞬时pHS升高; CO2外排则相反。在CO2的添加和去除过程中，CA II增加了最大pH变化速率（dpHi/dt）max和最大pHS变化ΔpHS。用抑制剂乙氧唑胺预孵育卵母细胞可消除CA II的影响。与pHS相比，pHi仅在延迟10.9s后才开始变化，并且其弛豫具有更大的（即，较慢）时间常数（τpHi> τpHS）。用两个pHi电极（一个表面电极和一个深度电极）同时测量表明，穿刺深度有助于pHidelay和更高的τpHi。使用更高的CO2/HCO 3 −水平，即，5%/33 mM HCO 3 −或10%/66 mM HCO 3 −增加（dpHi/dt）max和ΔpHS，但与[CO2]的增加不成比例。反应-扩散数学模型（在本系列第三篇论文中描述）解释了上述一般特征，并支持这样的结论：细胞质CA消耗进入的CO2或补充退出的CO2-增加了穿过细胞膜的CO2通量。
The α-carbonic anhydrases (CAs) are zinc-containing enzymes that catalyze the interconversion of CO2and HCO3−. Here, we focus on human CA II (CA II), a ubiquitous cytoplasmic enzyme. In the second paper in this series, we examine CA IV at the extracellular surface. After microinjecting recombinant CA II in a Tris solution (or just Tris) into oocytes, we expose oocytes to 1.5% CO2/10 mM HCO3−/pH 7.50 while using microelectrodes to monitor intracellular pH (pHi) and surface pH (pHS). CO2influx causes the familiar sustained pHifall as well as a transient pHSrise; CO2efflux does the opposite. Both during CO2addition and removal, CA II increases the magnitudes of the maximal rate of pHichange, (dpHi/dt)max, and the maximal change in pHS, ΔpHS. Preincubating oocytes with the inhibitor ethoxzolamide eliminates the effects of CA II. Compared with pHS, pHibegins to change only after a delay of ∼9 s and its relaxation has a larger (i.e., slower) time constant (τpHi> τpHS). Simultaneous measurements with two pHielectrodes, one superficial and one deep, suggest that impalement depth contributes to pHidelay and higher τpHi. Using higher CO2/HCO3−levels, i.e., 5%/33 mM HCO3−or 10%/66 mM HCO3−, increases (dpHi/dt)maxand ΔpHS, though not in proportion to the increase in [CO2]. A reaction-diffusion mathematical model (described in the third paper in this series) accounts for the above general features and supports the conclusion that cytosolic CA—consuming entering CO2or replenishing exiting CO2—increases CO2fluxes across the cell membrane.