With the rapid-freeze, deep-etch replica technique, the structural conformations of outer dynein arms in demembranated cilia from Tetrahymena were analyzed under two different conditions, i.e., in the absence of ATP and in the presence of ATP and vanadate. In the absence of ATP, the lateral view of axonemes was characterized by the egg- shaped outer dynein arms, which showed a slightly baseward tilt with a mean inclination of 11.1 degrees +/- 3.4 degrees SD from the perpendicular to the doublet microtubules. On the other hand, in the presence of 1 mM ATP and 100 microM vanadate, the outer arms were extended and slender and showed an increased baseward tilt with a mean inclination of 31.6 degrees +/- 4.9 degrees SD. In ATP-activated axonemes, these two types of arms coexisted, each type occurring in groups along one row of outer arms. These findings strongly suggest that the interdoublet sliding is caused by dynamic structural changes of dynein arms that follow the hydrolysis of ATP.
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机译：使用快速冷冻，深蚀刻复制技术，在两种不同条件下，即在没有ATP的情况下以及在ATP和钒酸盐的存在下，对来自四膜虫的去膜纤毛中达因素外臂的结构构象进行了分析。在不存在ATP的情况下，轴突的侧面特征是卵形的外部动力蛋白，其臂向外侧倾斜，从垂直于双峰微管的平均倾斜角度为11.1 +/- 3.4度SD。另一方面，在1 mM ATP和100 microM钒酸盐的存在下，外臂伸长且细长，并显示出增加的向内倾斜，平均倾斜度为SD的31.6度+/- 4.9度。在ATP激活的轴突中，这两种类型的臂共存，每种类型沿一组外臂成组出现。这些发现强烈表明，双联体间的滑动是由ATP水解后动力蛋白臂的动态结构变化引起的。
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