Regnier M, Lee D M, Homsher E
Department of Physiology, School of Medicine, University of California, Los Angeles 90095, USA.
Biophys J. 1998 Jun;74(6):3044-58. doi: 10.1016/S0006-3495(98)78012-9.
The mechanical behavior of skinned rabbit psoas muscle fiber contractions and in vitro motility of F-actin (Vf) have been examined using ATP, CTP, UTP, or their 2-deoxy forms (collectively designated as nucleotide triphosphates or NTPs) as contractile substrates. Measurements of actin-activated heavy meromyosin (HMM) NTPase, the rates of NTP binding to myosin and actomyosin, NTP-mediated acto-HMM dissociation, and NTP hydrolysis by acto-HMM were made for comparison to the mechanical results. The data suggest a very similar mechanism of acto-HMM NTP hydrolysis. Whereas all NTPs studied support force production and stiffness that vary by a factor 2 or less, the unloaded shortening velocity (Vu) of muscle fibers varies by almost 10-fold. 2-Deoxy ATP (dATP) was unique in that Vu was 30% greater than with ATP. Parallel behavior was observed between Vf and the steady-state maximum actin-activated HMM ATPase rate. Further comparisons suggest that the variation in force correlates with the rate and equilibrium constant for NTP cleavage; the variations in Vu or Vf are related to the rate of cross-bridge dissociation caused by NTP binding or to the rate(s) of product release.
已使用ATP、CTP、UTP或其2-脱氧形式（统称为三磷酸核苷酸或NTP）作为收缩底物，研究了去皮兔腰大肌纤维收缩的力学行为以及F-肌动蛋白（Vf）的体外运动性。对肌动蛋白激活的重酶解肌球蛋白（HMM）NTP酶、NTP与肌球蛋白和肌动球蛋白的结合速率、NTP介导的肌动蛋白-HMM解离以及肌动蛋白-HMM的NTP水解进行了测量，以便与力学结果进行比较。数据表明肌动蛋白-HMM NTP水解的机制非常相似。虽然所研究的所有NTP都支持产生力和刚度，其变化因子为2或更小，但肌肉纤维的无负荷缩短速度（Vu）变化近10倍。2-脱氧ATP（dATP）的独特之处在于，Vu比ATP时大30%。在Vf和稳态最大肌动蛋白激活的HMM ATP酶速率之间观察到平行行为。进一步的比较表明，力的变化与NTP裂解的速率和平衡常数相关；Vu或Vf的变化与NTP结合引起的横桥解离速率或产物释放速率有关。
