Catch contraction of bivalve adductor muscle by "Catch proteins"

众所周知，双壳类平滑肌内收肌表现为捕获性收缩，即一种节能的延长收缩状态。在本项目中，我们从调控蛋白参与渔获收缩的角度研究了渔获机制。研究了海蛤平滑肌中肌钙蛋白和其他肌动蛋白结合蛋白的分离。这种肌肉似乎缺乏肌钙蛋白，因为其固有的细纤维和肌钙蛋白部分不能赋予Ca^<2+>-对兔肌动球蛋白的敏感性。然而，足部肌肉中含有160kDa的肌动蛋白结合蛋白（ABP），与肌动蛋白共沉淀形成浑浊。生理条件下，ABP可使f - actin丝成束。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“闩锁蛋白”的候选蛋白，但ABP的其他特性却不同。因此，ABP与f -肌动蛋白的结合不受Ca^<2+>-钙调蛋白的影响，而且ABP的氨基酸组成与钙调蛋白有很大的不同。这些结果表明APB与caldesmon是不同类型的肌动蛋白捆绑蛋白。abp样蛋白被证明存在于各种双壳类动物中，如扇贝、贻贝、牡蛎和肋柜。为了明确ABP的肌动蛋白捆绑特性与捕集收缩之间的关系，还需要进一步的生理生化研究。由19kDa肌钙蛋白- i （19-Tnl）和4OkDa肌钙蛋白- t （40-TnT）组成的二元复合物与肌钙蛋白共纯化，形成赤原扇贝内收肌的粗肌钙蛋白部分。该复合物不能对兔重组肌动球蛋白mg - atp酶活性赋予Ca^<2+>-敏感性，但能够与赤原扇贝肌钙蛋白- c进一步络合。通过与赤原扇贝肌钙蛋白亚基的杂交，分离得到的19-Tnl和40-TnT分别能够替代肌钙蛋白- i和肌钙蛋白- t。我们可以认为19- tnao - tnl二元复合物以某种不同于肌钙蛋白的方式参与肌动蛋白的调控。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