The production of concentration P.D.'s across the skin of the frog is very intimately related to the pH of the applied solutions. On the alkaline side of an isoelectric point the dilute solution is electropositive; on the acid side this solution becomes electronegative. When the pH is suddenly lowered from a value more alkaline than this isoelectric point to one considerably more acid the change in polarity may occur within a few seconds. The effect is reversible. When a series of unbuffered solutions at different pH values are applied reversal curves may be obtained. When the concentration gradient is .1 N-.001 N KCl the reversal points lie between pH 4.1 and 4.8. When studied in acetate buffers this electromotive reversal is found to be closely correlated with the electrical charge upon the membrane, as determined by electroendosmosis through it. Reversal occurs between pH 4.9 and 5.2. It is concluded that the electromotive behavior of this material is controlled by some ampholyte, or group of ampholytes, within the membrane. This ampholyte is probably a protein. On both sides of their isoelectric point these membranes, in common with protein membranes, behave as if they retarded or prevented the movement through them of ions of the same electrical sign as they themselves bear, while permitting the movement of ions of the opposite sign. It is suggested that this correlation arises because of electrostatic effects between the charged surfaces and ions in the solution.
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机译:青蛙皮肤上浓度P.D.的产生与所用溶液的pH密切相关。在等电点的碱侧,稀溶液是正电的。在酸侧,该溶液变为负电。当pH突然从比该等电点更碱性的值降低到一个更大的酸时,极性的变化可能会在几秒钟内发生。效果是可逆的。当应用一系列在不同pH值的非缓冲溶液时,可得到逆转曲线。当浓度梯度为0.1 N-.001 N KCl时,反转点位于pH 4.1和4.8之间。当在醋酸盐缓冲液中进行研究时,发现这种电动势的逆转与膜上的电荷密切相关,这取决于通过膜的电渗透。在pH 4.9和5.2之间发生逆转。结论是,该材料的电动势受膜内某些两性电解质或两性电解质的控制。该两性电解质可能是蛋白质。这些膜在其等电点的两侧,与蛋白质膜一样,表现得像是阻碍或阻止了与它们本身具有相同电符号的离子通过它们的运动,同时允许相反符号的离子运动。提出这种相关性是由于带电表面和溶液中离子之间的静电作用而产生的。
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