Shiner J S, Solaro R J
Biophys J. 1984 Oct;46(4):541-3. doi: 10.1016/S0006-3495(84)84051-5.
The following arguments are presented for the observation that curves relating free Ca2+ and force development of thin filament regulated myofilaments of skinned muscle fibers have Hill coefficient (n) greater than 4, which is the number of Ca2+ binding sites on troponin: Activation of the myofilaments is a process relaxing to a nonequilibrium steady state or stationary state. Systems operating at nonequilibrium stationary states are known to display Hill coefficients greater than the number of interacting sites and similar results have been obtained for Ca2+ activation of myofilament isometric force. The size of the basic subunit of thin filament regulated muscle may be the entire thin filament rather than seven actins, one tropomyosin, and one troponin. In this case the number of interacting sites may be on the order of hundreds. Hysteresis in the Ca2+ activation of isometric force might result from multiple stationary states and also might give rise to Hill coefficients greater than 4.
与游离钙离子和经皮肌纤维细丝调节的肌丝的力发展相关的曲线具有大于4的希尔系数（n），而4是肌钙蛋白上钙离子结合位点的数量：肌丝的激活是一个松弛到非平衡稳态或静止状态的过程。已知在非平衡稳态下运行的系统会显示出大于相互作用位点数量的希尔系数，并且在肌丝等长力的钙离子激活方面也获得了类似的结果。细丝调节肌肉的基本亚基大小可能是整个细丝，而不是七个肌动蛋白、一个原肌球蛋白和一个肌钙蛋白。在这种情况下，相互作用位点的数量可能在数百个左右。等长力的钙离子激活中的滞后现象可能源于多个静止状态，也可能导致希尔系数大于4。
