The actin-activated Mg2+-ATPase activity of gizzard HMM increased in proportion to the square of the extent of LC phosphorylation. This result indicates that the LCs of HMM are randomly phosphorylated, and the phosphorylation of both heads of HMM is required for the activation of HMM Mg2+-ATPase by F-actin. 2. In 75 mM KCl, the Mg2+-ATPase activity of gizzard myosin was activated by F-actin only slightly when a half of the total LC was phosphorylated. From 1 to 2 mol LC phosphorylation, the activity was enhanced by F-actin almost linearly. In 30 mM KCl, the activity of acto-gizzard myosin increased sigmoidally with increase in the extent of LC phosphorylation. On electron microscopy, side-by-side aggregates of myosin filaments were observed in 30 mM KCl, but not in 75 mM KCl. It was suggested that the activation of the Mg2+-ATPase activity of acto-gizzard myosin LC phosphorylation is modified by formation of myosin filaments and their aggregates. 3. The relationship between the actin-activated Mg2+-ATPase activity of HMM or myosin and the extent of LC phosphorylation was unaffected by tropomyosin.
摘要
砂囊重酶解肌球蛋白的肌动蛋白激活的Mg2+ -ATP酶活性与轻链磷酸化程度的平方成正比。这一结果表明，重酶解肌球蛋白的轻链是随机磷酸化的，并且重酶解肌球蛋白两个头部的磷酸化是F -肌动蛋白激活重酶解肌球蛋白Mg2+ -ATP酶所必需的。2. 在75 mM KCl中，当总轻链的一半被磷酸化时，砂囊肌球蛋白的Mg2+ -ATP酶活性仅被F -肌动蛋白轻微激活。从1到2摩尔轻链磷酸化，F -肌动蛋白使活性几乎呈线性增强。在30 mM KCl中，肌动蛋白-砂囊肌球蛋白的活性随着轻链磷酸化程度的增加呈S形增加。在电子显微镜下，在30 mM KCl中观察到肌球蛋白丝的并排聚集体，而在75 mM KCl中未观察到。有人认为，肌动蛋白-砂囊肌球蛋白轻链磷酸化的Mg2+ -ATP酶活性的激活因肌球蛋白丝及其聚集体的形成而改变。3. 原肌球蛋白不影响重酶解肌球蛋白或肌球蛋白的肌动蛋白激活的Mg2+ -ATP酶活性与轻链磷酸化程度之间的关系。
