Bullard B, Bell J, Craig R, Leonard K
J Mol Biol. 1985 Apr 5;182(3):443-54. doi: 10.1016/0022-2836(85)90203-7.
There are one or more proteins of 50,000 to 60,000 Mr in the thin filaments of insect flight muscle. A protein of 55,000 Mr has been isolated from insect fibrillar flight muscle and called arthrin. Despite its higher molecular weight, arthrin is in many ways like actin. The amino acid composition of arthrin was similar to that of actin. There were similarities in the peptides produced by digesting the denatured proteins and mild digestion of polymerized proteins cleaved similar-sized fragments from arthrin and actin. Polymerized arthrin activated the Mg2+ ATPase of myosin to the same extent as actin and the ATPase was regulated by rabbit or Lethocerus troponin and tropomyosin. Arthrin did not itself act as troponin-T. Electron microscopy of negatively stained specimens showed that arthrin and actin filaments were similar in structure and that arthrin could be decorated by rabbit subfragment-1 to form normal-looking arrowheads. Arthrin formed paracrystals at an optimum concentration of MgCl2 (25 mM) that was somewhat lower than the optimum for actin paracrystals. Optical diffraction showed that the structure of the paracrystals was similar to those formed from actin. The mass of arthrin and actin filaments relative to phage fd was measured by scanning transmission electron microscopy; the relative mass of arthrin and actin was 1.33, in agreement with molecular weight estimations. Therefore arthrin has the properties of a heavy form of actin. The proportion of actin, arthrin and troponin-T in Lethocerus myofibrils was six moles of actin to one mole of arthrin and one mole of troponin-T. The function of arthrin is not known.
昆虫飞行肌细肌丝中存在一种或多种分子量在50,000至60,000道尔顿之间的蛋白质。一种分子量为55,000道尔顿的蛋白质已从昆虫纤维状飞行肌中分离出来，并被称为节肢蛋白。尽管节肢蛋白分子量较高，但在许多方面与肌动蛋白相似。节肢蛋白的氨基酸组成与肌动蛋白相似。消化变性蛋白产生的肽段存在相似性，对聚合蛋白的温和消化从节肢蛋白和肌动蛋白上切割下了相似大小的片段。聚合的节肢蛋白激活肌球蛋白的Mg2+ATP酶的程度与肌动蛋白相同，并且该ATP酶受兔或大仰蝽肌钙蛋白和原肌球蛋白调节。节肢蛋白本身并不充当肌钙蛋白-T。负染标本的电子显微镜观察表明，节肢蛋白丝和肌动蛋白丝在结构上相似，并且节肢蛋白可以被兔肌球蛋白亚片段-1标记形成外观正常的箭头。节肢蛋白在MgCl2（25 mM）的最佳浓度下形成副晶体，该浓度略低于肌动蛋白副晶体的最佳浓度。光学衍射表明，副晶体的结构与由肌动蛋白形成的副晶体相似。通过扫描透射电子显微镜测量节肢蛋白丝和肌动蛋白丝相对于噬菌体fd的质量；节肢蛋白和肌动蛋白的相对质量为1.33，与分子量估计值一致。因此，节肢蛋白具有重形式肌动蛋白的特性。大仰蝽肌原纤维中肌动蛋白、节肢蛋白和肌钙蛋白-T的比例为6摩尔肌动蛋白比1摩尔节肢蛋白和1摩尔肌钙蛋白-T。节肢蛋白的功能尚不清楚。
