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在体外零负荷条件下,平滑肌和骨骼肌肌球蛋白均表现出较低的工作循环。

Smooth and skeletal muscle myosin both exhibit low duty cycles at zero load in vitro.

作者信息

Harris D E, Warshaw D M

机构信息

Department of Molecular Physiology and Biophysics, University of Vermont, Burlington 05405.

出版信息

J Biol Chem. 1993 Jul 15;268(20):14764-8.

PMID:8325853
Abstract

Smooth muscle's stress equals that of skeletal muscle with less myosin. Thus, under isometric conditions, smooth muscle myosin may spend a greater fraction of its cycle time attached to actin in a high force state (i.e. higher duty cycle). If so, then smooth muscle myosin may also have a higher duty cycle under unloaded conditions. To test this, we used an in vitro motility assay in which fluorescently labeled actin filaments move freely over a sparsely coated (5-100 micrograms/ml) myosin surface. Actin filament velocity (V) was a function of the number of cross-bridges capable of interacting with an actin filament (N) and the duty cycle (f), V = (a x Vmax) x (1-(1-f)N) (Uyeda et al., 1990; Harada et al., 1990). N was estimated from the myosin density on the motility surface and the actin filament length. Data for V versus N were fit to the above equation to predict f. The duty cycle of smooth muscle myosin (4.0 +/- 0.7%) was not significantly different from that of skeletal muscle myosin (3.8 +/- 0.5%) in agreement with values estimated by Uyeda et al. (1990) for skeletal muscle myosin under unloaded conditions. The duty cycles of smooth and skeletal muscle myosin may still differ under isometric conditions.

摘要

平滑肌的应力与肌球蛋白较少的骨骼肌的应力相当。因此,在等长条件下,平滑肌肌球蛋白在其循环时间内可能会有更大比例以高力状态附着于肌动蛋白(即更高的占空比)。如果是这样,那么在无负载条件下平滑肌肌球蛋白可能也具有更高的占空比。为了验证这一点,我们使用了一种体外运动分析方法,其中荧光标记的肌动蛋白丝在稀疏包被(5 - 100微克/毫升)的肌球蛋白表面自由移动。肌动蛋白丝速度(V)是能够与肌动蛋白丝相互作用的横桥数量(N)和占空比(f)的函数,V = (a × Vmax) × (1 - (1 - f)N)(上田等人,1990年;原田等人,1990年)。N是根据运动表面上的肌球蛋白密度和肌动蛋白丝长度估算得出的。将V与N的数据拟合到上述方程以预测f。平滑肌肌球蛋白的占空比(4.0 ± 0.7%)与骨骼肌肌球蛋白的占空比(3.8 ± 0.5%)无显著差异,这与上田等人(1990年)对无负载条件下骨骼肌肌球蛋白估算的值一致。在等长条件下,平滑肌和骨骼肌肌球蛋白的占空比可能仍然存在差异。

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