Armstrong C M, Bezanilla F, Rojas E
J Gen Physiol. 1973 Oct;62(4):375-91. doi: 10.1085/jgp.62.4.375.
We have studied the effects of the proteolytic enzyme Pronase on the membrane currents of voltage-clamped squid axons. Internal perfusion of the axons with Pronase rather selectively destroys inactivation of the Na conductance (g(Na)). At the level of a single channel, Pronase probably acts in an all-or-none manner: each channel inactivates normally until its inactivation gate is destroyed, and then it no longer inactivates. Pronase reduces g(Na), possibly by destroying some of the channels, but after removal of its inactivation gate a Na channel seems no longer vulnerable to Pronase. The turn-off kinetics and the voltage dependence of the Na channel activation gates are not affected by Pronase, and it is probable that the enzyme does not affect these gates in any way. Neither the K channels nor their activation gates are affected in a specific way by Pronase. Tetrodotoxin does not protect the inactivation gates from Pronase, nor does maintained inactivation of the Na channels during exposure to Pronase. Our results suggest that the inactivation gate is a readily accessible protein attached to the inner end of each Na channel. It is shown clearly that activation and inactivation of Na channels are separable processes, and that Na channels are distinct from K channels.
我们研究了蛋白水解酶链霉蛋白酶对电压钳制的枪乌贼轴突膜电流的影响。用链霉蛋白酶对轴突进行内部灌注，会选择性地破坏钠电导（g(Na)）的失活。在单通道水平上，链霉蛋白酶可能以全或无的方式起作用：每个通道在其失活门被破坏之前正常失活，之后就不再失活。链霉蛋白酶可能通过破坏一些通道来降低g(Na)，但在去除其失活门后，钠通道似乎不再易受链霉蛋白酶的影响。钠通道激活门的关闭动力学和电压依赖性不受链霉蛋白酶影响，并且该酶很可能不会以任何方式影响这些门。链霉蛋白酶对钾通道及其激活门均无特定影响。河豚毒素不能保护失活门免受链霉蛋白酶的作用，在暴露于链霉蛋白酶期间钠通道的持续失活也不能。我们的结果表明，失活门是一种易于接近的蛋白质，附着在每个钠通道的内端。结果清楚地表明，钠通道的激活和失活是可分离的过程，并且钠通道与钾通道不同。
