Norris F A, Powell G L
Department of Biological Sciences, Clemson University, SC 29634-1903.
Biochim Biophys Acta. 1990 Nov 30;1030(1):165-71. doi: 10.1016/0005-2736(90)90252-j.
A dioleoylphosphatidylcholine unilamellar vesicle model system was used to determine proton permeability. The fluorescence of the pH reporter group, pyranine, trapped within vesicles with a difference in pH across the bilayer, was digitized and analyzed with numerical integration. When H+ flux was initiated by the acidification of the external buffer (acid jump), the apparent H+ permeability was found to be a linear function of the reciprocal of the internal H+ concentration with the slope inversely proportional to the initial size of the H+ gradient. When flux was initiated by the alkalinization of the external buffer (base jump), the apparent permeability coefficient was constant for each external H+ concentration. However, the value of the apparent permeability was linearly dependent on the reciprocal of the external H+. The possibility that carbonates (carbon dioxide, carbonic acid, bicarbonate and carbonate) could be acting as proton carriers was tested by adding millimolar concentrations of bicarbonate to solutions greatly reduced in carbonates. The slopes of the graphs of apparent permeability coefficient vs. reciprocal H+ were linear functions of added bicarbonate concentration for both acid and base jump conditions. These observations were interpreted in terms of a model suggesting that carbonic acid or carbon dioxide together with bicarbonate was an efficient proton carrier across phospholipid bilayers.
使用二油酰磷脂酰胆碱单层囊泡模型系统来测定质子渗透性。将被困在双层膜两侧pH存在差异的囊泡内的pH报告基团吡喃荧光数字化，并通过数值积分进行分析。当通过酸化外部缓冲液引发H⁺通量（酸跃变）时，发现表观H⁺渗透性是内部H⁺浓度倒数的线性函数，其斜率与H⁺梯度的初始大小成反比。当通过碱化外部缓冲液引发通量（碱跃变）时，对于每个外部H⁺浓度，表观渗透系数是恒定的。然而，表观渗透率的值与外部H⁺的倒数呈线性相关。通过向碳酸盐含量大大降低的溶液中添加毫摩尔浓度的碳酸氢盐，测试了碳酸盐（二氧化碳、碳酸、碳酸氢盐和碳酸盐）可能作为质子载体的可能性。在酸跃变和碱跃变条件下，表观渗透系数与H⁺倒数的关系图的斜率均为添加碳酸氢盐浓度的线性函数。这些观察结果根据一个模型进行了解释，该模型表明碳酸或二氧化碳与碳酸氢盐一起是跨磷脂双层的有效质子载体。
