Yamashita H, Sugiura S, Serizawa T, Sugimoto T, Iizuka M, Katayama E, Shimmen T
Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Am J Physiol. 1992 Aug;263(2 Pt 2):H464-72. doi: 10.1152/ajpheart.1992.263.2.H464.
To investigate the relationship between the mechanical and biochemical properties of cardiac myosin, the sliding velocity of isolated cardiac myosin obtained from both euthyroid and hyperthyroid rabbits on actin cables was measured with an in vitro motility assay system. Ten rabbits (T) were treated with L-thyroxine to induce hyperthyroidism, and eight nontreated animals (N) were used as controls. Myosin was purified from the left ventricles of anesthetized animals. Myosin isozyme content was analyzed by the pyrophosphate gel electrophoresis method, and myosin adenosinetriphosphatase (ATPase) activity was determined on the same sample. Long well-organized actin cables of green algae, Nitellopsis, were used in the in vitro motility assay. Small latex beads were coated with purified cardiac myosin and introduced onto the Nitellopsis actin cables. Active unidirectional movement of the beads on the actin cables was observed under a photomicroscope, and the velocity was measured. The velocity was dependent on ATP concentrations, and the optimal pH for bead movement was approximately 7.0-7.5. The mean velocity was higher in T than in N (0.66 +/- 0.12 vs. 0.32 +/- 0.09 micron/s, P less than 0.01). Both Ca(2+)-activated ATPase activity and the percentage of alpha-myosin heavy chain were also higher in T than in N (0.691 +/- 0.072 vs. 0.335 +/- 0.072 microM Pi.mg-1.min-1, P less than 0.01, and 79 +/- 12 vs. 26 +/- 7%, P less than 0.01, respectively). The velocity of myosin closely correlated with both Ca(+2)-activated myosin ATPase activity (r = 0.87, P less than 0.01) and the percentage of alpha-myosin heavy chain (r = 0.87, P less than 0.01).
为了研究心肌肌球蛋白的机械和生化特性之间的关系，使用体外运动分析系统测量了从甲状腺功能正常和甲状腺功能亢进的兔子中分离得到的心肌肌球蛋白在肌动蛋白丝上的滑动速度。10只兔子（T组）用左旋甲状腺素治疗以诱导甲状腺功能亢进，8只未治疗的动物（N组）用作对照。从麻醉动物的左心室中纯化肌球蛋白。通过焦磷酸凝胶电泳法分析肌球蛋白同工酶含量，并在同一样品上测定肌球蛋白腺苷三磷酸酶（ATP酶）活性。在体外运动分析中使用了绿藻Nitellopsis中排列良好的长肌动蛋白丝。将小乳胶珠用纯化的心肌肌球蛋白包被，然后置于Nitellopsis肌动蛋白丝上。在光学显微镜下观察到珠子在肌动蛋白丝上的主动单向运动，并测量速度。速度取决于ATP浓度，珠子运动的最佳pH约为7.0 - 7.5。T组的平均速度高于N组（0.66±0.12对0.32±0.09微米/秒，P<0.01）。T组的钙激活ATP酶活性和α-肌球蛋白重链百分比也高于N组（分别为0.691±0.072对0.335±0.072微摩尔无机磷·毫克-1·分钟-1，P<0.01，以及79±12对26±7%，P<0.01）。肌球蛋白的速度与钙激活的肌球蛋白ATP酶活性（r = 0.87，P<0.01）和α-肌球蛋白重链百分比（r = 0.87，P<0.01）密切相关。
