Cavadore J C, Berta P, Axelrud-Cavadore C, Haiech J
Biochemistry. 1985 Sep 10;24(19):5216-21. doi: 10.1021/bi00340a039.
Bovine aortic tropomyosin has been isolated by DEAE-Sepharose chromatography following isoelectric precipitation and ammonium sulfate fractionation. A single polypeptide [Mr 36 000 on a sodium dodecyl sulfate (SDS)-polyacrylamide gel] was obtained under different electrophoretic conditions. The amino acid composition of bovine tropomyosin was very similar to that of rabbit skeletal muscle; the amino-terminal residue is blocked. The molecular weight of the native tropomyosin (76 000), which is twice that calculated from the SDS-polyacrylamide gel, suggests that the molecule is a dimer. The diffusion coefficient of 3.4 X 10(-7) cm2 s-1 and the frictional coefficient of 1.7 indicate that the molecule is asymmetric. Comparative high-pressure liquid chromatography peptide mapping of rabbit skeletal and bovine aortic tropomyosins shows primary structure variation. Bovine aortic tropomyosin binds calcium under physiological conditions of pH and ionic strength (22 mol of Ca2+/mol of tropomyosin with a Kd of 1.4 mM). Such a property is not shared by skeletal tropomyosin. In low Mg2+ concentration, both skeletal and aortic actin activations of the skeletal myosin ATPase activity are calcium independent. Addition of aortic tropomyosin to a hybrid actomyosin (aortic actin, skeletal myosin) yields an enhancement of the actin activation of the myosin ATPase activity, but the addition of skeletal tropomyosin yields a decrease of this activity. However, both the enhancement and decrease are calcium dependent. Addition of skeletal or aortic tropomyosin to an actomyosin system, where both actin and myosin come from skeletal muscle, yields only an enhancement of the actin activation of the myosin ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
牛主动脉原肌球蛋白是通过离子交换沉淀和硫酸铵分级分离后，再经二乙氨基乙基葡聚糖凝胶（DEAE - Sepharose）柱层析分离得到的。在不同的电泳条件下，获得了一条单一的多肽链（在十二烷基硫酸钠 - 聚丙烯酰胺凝胶上的分子量为36000）。牛原肌球蛋白的氨基酸组成与兔骨骼肌的非常相似；氨基末端残基被封闭。天然原肌球蛋白的分子量为76000，是根据十二烷基硫酸钠 - 聚丙烯酰胺凝胶计算值的两倍，这表明该分子是二聚体。扩散系数为3.4×10⁻⁷ cm²·s⁻¹，摩擦系数为1.7，表明该分子是不对称的。兔骨骼肌和牛主动脉原肌球蛋白的高压液相色谱肽图比较显示出一级结构的差异。在生理pH和离子强度条件下（每摩尔原肌球蛋白结合22摩尔Ca²⁺，解离常数Kd为1.4 mM），牛主动脉原肌球蛋白能结合钙。骨骼肌原肌球蛋白不具有这种特性。在低镁离子浓度下，骨骼肌肌动蛋白和主动脉肌动蛋白对骨骼肌肌球蛋白ATP酶活性的激活均不依赖钙。向混合肌动球蛋白（主动脉肌动蛋白、骨骼肌肌球蛋白）中添加主动脉原肌球蛋白可增强肌球蛋白ATP酶活性对肌动蛋白的激活作用，但添加骨骼肌原肌球蛋白则会降低该活性。然而，增强和降低均依赖钙。向肌动球蛋白系统（其中肌动蛋白和肌球蛋白均来自骨骼肌）中添加骨骼肌或主动脉原肌球蛋白，只会增强肌球蛋白ATP酶活性对肌动蛋白的激活作用。（摘要截短于250字）
