阿米巴样运动的收缩基础。VI. 溶胶-收缩偶联假说。

The contractile basis of ameboid movement. VI. The solation-contraction coupling hypothesis.

作者信息

Hellewell S B, Taylor D L

出版信息

J Cell Biol. 1979 Dec;83(3):633-48. doi: 10.1083/jcb.83.3.633.

DOI:10.1083/jcb.83.3.633

PMID:42649

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC2110508/

Abstract

The contracted pellets derived from a high-speed supernate of Dictyostelium discoideum (S3) were investigated to determine the functional activity associated with this specific subset of the cellular motile apparatus. A partially purified model system of gelation and contraction (S6) was prepared from the contracted pellets, and the presence of calcium- and pH-sensitive gelation and contraction in this model demonstrated that a functional cytoskeletal-contratile complex remained at least partially associated with the actin and myosin during contraction. Semi-quantitative assays of gelation and solation in the myosin-free preparation S6 included measurements of turbidity, relative viscosity, and strain birefringence. The extent of gelation was optimal at pH 6.8 and a free calcium ion concentration of approximately 3.0 x 10(-8) M. Solation was favored when the free calcium ion concentration was greater than 7.6 x 10(-7) M or when the pH was increased or decreased from pH 6.8. Gelation was reversibly inhibited by increasing the free calcium ion concentration to approxomately 4.6 x 10(-6) M at pH 6.8. The solation-gelation process of this model has been interpreted to involve the reversible cross-linking of actin filaments. The addition of purified D. discoideum myosin to S6 served to reconstitute calcium- and pH-regulated contraction. The results from this study indicate that contraction is coupled functionally to the local breakdown (solation) of the gel. Therefore, solation has been identified as a structural requirement for extensive shortening during contraction. We have called this concept the solation-contraction coupling hypothesis. Fractionation of a preparation derived from the contracted pellets yielded a fraction consisting of actin and a 95,000-dalton polypeptide that exhibited calcium-sensitive gelation at 28 degrees C and a fraction composed of actin and 30,000- and 18,000-dalton polypeptides that demonstrated calcium-sensitive genlation at 0 degrees C.

摘要

对源自盘基网柄菌高速上清液的收缩小球（S3）进行了研究，以确定与细胞运动装置这一特定亚集相关的功能活性。从收缩小球制备了凝胶化和收缩的部分纯化模型系统（S6），该模型中钙敏感和pH敏感的凝胶化及收缩现象表明，在收缩过程中，功能性细胞骨架收缩复合物至少部分与肌动蛋白和肌球蛋白相关联。无肌球蛋白制剂S6中凝胶化和溶胶化的半定量测定包括浊度、相对粘度和应变双折射的测量。凝胶化程度在pH 6.8和游离钙离子浓度约为3.0×10⁻⁸ M时最佳。当游离钙离子浓度大于7.6×10⁻⁷ M或pH从pH 6.8升高或降低时，溶胶化更有利。在pH 6.8时，将游离钙离子浓度增加到约4.6×10⁻⁶ M可可逆地抑制凝胶化。该模型的溶胶化-凝胶化过程被解释为涉及肌动蛋白丝的可逆交联。向S6中添加纯化的盘基网柄菌肌球蛋白可重建钙和pH调节的收缩。这项研究的结果表明，收缩在功能上与凝胶的局部分解（溶胶化）相关联。因此，溶胶化已被确定为收缩过程中广泛缩短的结构要求。我们将这一概念称为溶胶化-收缩偶联假说。对源自收缩小球的制剂进行分级分离，得到一个由肌动蛋白和一种在28℃表现出钙敏感凝胶化的95,000道尔顿多肽组成的级分，以及一个由肌动蛋白和30,000道尔顿及18,000道尔顿多肽组成的级分，该级分在0℃表现出钙敏感凝胶化。