Yeh Y, Baskin R J, Burton K, Chen J S
Biophys J. 1987 Mar;51(3):439-47. doi: 10.1016/S0006-3495(87)83365-9.
The polarization properties of light diffracted from single-skinned fibers of skeletal muscles have been examined under conditions in which the bathing solution pH and the ionic strength are changed. For fibers in the relaxed state, we observe large decreases in both the total depolarization signal, r, and the total diffraction birefringence signal, delta nT, upon pH change from 7.0 to 8.0 at normal ionic strength. However, if the ionic strength is raised, then the r-value change as the pH changes from pH 7.0 to pH 8.0 is much smaller. If the rigor state is achieved at pH 8.0, and 0 mM ATP under either of the ionic strength conditions, the fiber can still be stretched. Rigor stiffness for this state is only approximately 20% that of the value of the stiffness at pH 7.0 rigor. Electron micrographs obtained under this pH 8.0 rigor state show that the overlap region can be decreased upon stretching the fiber, signifying a different kind of weaker-binding rigor state. Optically, the weaker-binding rigor state has a lower depolarization signal and larger form birefringence than the strong-binding rigor state. To convert from one type of rigor state (pH 7.0) to the other rigor state (pH 8.0), or vice versa, the fiber must first be relaxed. Apparently, either of the rigor states can block the full impact of the pH effect.
在改变浴液pH值和离子强度的条件下，研究了从骨骼肌单皮纤维衍射的光的偏振特性。对于处于松弛状态的纤维，我们观察到在正常离子强度下，当pH值从7.0变为8.0时，总去极化信号r和总衍射双折射信号δnT均大幅下降。然而，如果提高离子强度，那么当pH值从7.0变为8.0时，r值的变化要小得多。如果在两种离子强度条件下，在pH 8.0和0 mM ATP时达到强直状态，纤维仍可被拉伸。此状态下的强直硬度仅约为pH 7.0强直时硬度值的20%。在这种pH 8.0强直状态下获得的电子显微镜照片显示，拉伸纤维时重叠区域会减小，这表明存在一种不同类型的弱结合强直状态。在光学上，与强结合强直状态相比，弱结合强直状态具有较低的去极化信号和较大的形状双折射。要从一种强直状态（pH 7.0）转换为另一种强直状态（pH 8.0），反之亦然，纤维必须首先松弛。显然，任何一种强直状态都可以阻断pH效应的全部影响。
