CHARACTERIZATION OF MYOSIN I

最近，已经确定有许多不同的成员 肌球蛋白超家族的成员。大多数具有特征性的肌球蛋白是 在结构上与脊椎动物骨骼肌肌球蛋白相似，因为它们 有两个球状的头域和一个长的杆状域， 缔合形成细丝。这些肌球蛋白由两个重的 200,000 Da链和4个轻链亚基。委员会的其他成员 肌球蛋白家族可能具有不同的结构。特别是，肌球蛋白I 来自棘阿米巴和脊椎动物的来源是单头的，有 比骨骼肌肌球蛋白的重链分子量低。 鸡肠道刷状缘上皮细胞含有肌球蛋白I 它有一条100 kDa的重链和三条钙调蛋白轻链。这 肌球蛋白不形成细丝，但有一种肌动蛋白激活 镁ATPase活性和肌动蛋白微丝移位的体外研究 运动性分析。镁ATPase活性的运动性和肌动蛋白激活 在高钙浓度下被抑制，这是由于 钙调素分子的一部分。钙调蛋白的重新添加 恢复镁ATPase活性的运动性和肌动蛋白激活。 原肌球蛋白与肌动蛋白细丝的结合也抑制了运动性和 肌动蛋白激活的镁ATP酶活性与肌动蛋白亲和力的降低 肌球蛋白。 我们已经开始了对肌球蛋白I的初步鉴定。 来自Nitella axillaris，一种经历了蓬勃发展的淡水绿藻 细胞质流动。Nitella提取液移位肌动蛋白细丝 在体外动力分析中以非常快的速度。这场运动不是 被钙离子抑制，而不是刷状边缘肌球蛋白。 正试图提纯这台马达以确定其特性。

Recently, it has been determined that there are many different members of the myosin superfamily. Most of the characterized myosins are structurally similar to vertebrate skeletal muscle myosin in that they have two globular head domains and a long rod-like domain which self associates to form filaments. These myosins are composed of two heavy chains of 200,000 Da and 4 light chain subunits. Other members of the myosin family may possess distinct structures. In particular, myosin I from Acanthamoeba and vertebrate sources are single-headed and have a lower molecular weight heavy chain than that of skeletal muscle myosin. Chicken intestinal brush border epithelial cells contain a myosin I which has a 100 kDa heavy chain and three calmodulin light chains. This myosin does not form filaments, but does have an actin-activated MgATPase activity and translocates actin filaments in an in vitro motility assay. Motility and actin-activation of the MgATPase activity is inhibited at high calcium concentrations due to a dissociation of a fraction of the calmodulin molecules. Re-addition of calmodulin restores motility and actin-activation of the MgATPase activity. Tropomyosin binding to the actin filaments also inhibits motility and actin-activated MgATPase activity and decreases the affinity of actin for myosin. We have begun the preliminary characterization of a putative myosin I from Nitella axillaris, a freshwater green alga which undergoes vigorous cytoplasmic streaming. Extracts of Nitella translocate actin filaments at a very fast rate in in vitro motility assays. The movement is not inhibited by calcium ions in contrast to the brush border myosin I. We are trying to purify this motor in order to characterize its properties.