Catch contraction of bivalve adductor muscle by "Catch proteins"

众所周知，双壳类闭壳平滑肌具有捕捉性收缩，即一种节能的长时间收缩状态。在本项目中，我们从调节蛋白参与捕获收缩的角度研究了捕获机制。研究了海蚌平滑肌以分离肌钙蛋白和其他肌动蛋白结合蛋白。该肌肉似乎缺乏肌钙蛋白，因为其自身的细丝和肌钙蛋白组分不能赋予兔肌动球蛋白Ca^2+敏感性。然而，足肌具有主要的160 kDa肌动蛋白结合蛋白（ABP），其与肌动蛋白共沉淀形成混浊。在生理条件下，ABP可使F-肌动蛋白纤维形成束。ABP的分子量和肌动蛋白结合特性与caldesmon相似，caldesmon被认为是脊椎动物平滑肌中的“闩锁蛋白”的候选者，但ABP的其他特性与caldesmon相似。 ...更多信息 没有因此，ABP与F-肌动蛋白的结合不受Ca^2+-钙调素的影响，ABP的氨基酸组成与钙调素的氨基酸组成完全不同。这些结果表明APB是一种不同于钙调素的肌动蛋白捆绑蛋白。ABP样蛋白在扇贝、贻贝、牡蛎、棱纹方舟等多种贝类中均有表达。为了明确ABP的肌动蛋白集束特性与渔获物收缩的关系，还需要进一步的生理生化研究.从赤栉孔扇贝闭壳肌肌钙蛋白粗提物中共纯化了由19 kDa肌钙蛋白-I（19-TnI）和40 kDa肌钙蛋白-T（40-TnT）组成的二元复合物。这种复合物不能赋予兔重组肌动球蛋白Mg-ATP酶活性Ca^<2+>-敏感性，但能够与赤原扇贝肌钙蛋白-C进一步复合。在与Akazara扇贝肌钙蛋白亚基杂交时，分离的19-TnI和40-TnT显示能够分别替代肌钙蛋白-I和肌钙蛋白-T。我们可以认为，19-TnIAO-Tnl二元复合物以与肌钙蛋白不同的方式参与肌动蛋白介导的调节。少

It is well-known that bivalve smooth adductor muscle show catch contraction, that is, an energy-saving prolonged state of contraction. In the present project, we have studied the catch mechanism from the standpoint of the participation of regulatory proteins in the catch contraction.1. Surf-clam smooth muscle was investigated to isolate the troponin and other actin-binding proteins. This muscle seemed to lack troponin because its native thin filament and troponin fraction were incapable of conferring Ca^<2+>-sensitivity to rabbit actomyosin. However, the foot muscle possesses major 160kDa actin binding protein (ABP) which was cosedimented with actin to form turbidity. The ABP was shown to make F-cactin filaments into bundiles under physiological conditions. The molecular weight and actin-bunding property of the ABP were similar to those of caldesmon which has been considered as a candidate for "latch proteins" in vertebrate smooth muscle, however, the other characteristics of ABP were … More not. Thus, the binding of ABP to F-actin was unaffected by Ca^<2+>-calmodulin and the amino acid composition of the ABP was quite different from that of caldesmon. These resu lts indicate that the APB is a different type of actin-bundling protein from caldesmon. The ABP-like proteins were shown to be present in various bivalves, such as scallop, mussel, oyster, and ribbed ark. To make clear the relationship between the actin-bundling property of ABP and the catch contraction, further physiological and biochemical studies are necessary.2. A binary complex consisting of 19kDa troponin-I(19-Tnl)and 4OkDa troponin-T(40-TnT)was co-purified with troponin form a crude troponin fraction of akazara scallop adductor muscle. This complex is incapable of conferring Ca^<2+>-sensitivity to rabbit reconstituted actomyosin Mg-ATPase activity, but became capable on further complexing with Akazara scallop troponin-C. On hybridization with the Akazara scallop troponin subunits, the isolated 19-Tnl and 40-TnT were shown to be able to substitute for troponin-I and troponin-T, respectively. We may consider that the 19-TnIAO-Tnl binary complex is implicated in the actin-finked regulation in somehow different manner from troponin. Less