Matsuno A, Kannda M, Okuda M
Department of Biological Sciences, Faculty of Life Science, Shimane University, Japan.
Tissue Cell. 1996 Aug;28(4):501-5. doi: 10.1016/s0040-8166(96)80036-x.
Catch muscles of molluscs usually have thick filaments of about 100 nm in diameter. The filament is constructed of a paramyosin core filament and an outer layer of myosin molecules. Myosin molecules are situated on the paramyosin core filament towards both ends, and they consequently have polarity towards both ends. According to our observations on the paramyosin core filaments from the native thick filaments, they bear regular cross-striations on their surfaces of about 14.5 nm periodicity when incubated in a KCl solution for a short time. The periodic pattern is supposed to be representative of peculiar arrangements of paramyosin molecules in the core, but the periodic pattern disappeared during incubation in a solution of high concentration KCl for a prolonged time, and a 'Bear-Selby net' pattern appeared substitutionally. These 'Bear-Selby net' patterns were conveniently divided into 3 types among 4 paramyosin core filaments from 4 'catch' muscles; the adductors of a pecten, an oyster and a clam, and the byssus retractor of a mussel. The 'Bear-Selby net' of an oyster resembled that of a pecten. Purified paramyosin crystals from the 4 muscles showed a common periodicity of about 72.5 nm. Electrophoresis with SDS of the 4 paramyosins on 6% polyacrylamide gels revealed molecular weights at 104 kD from a pecten, 105 kD from an oyster, 103 kD from a clam and 105 kD from a mussel.
软体动物的捕捉肌通常具有直径约100纳米的粗肌丝。这种肌丝由一条副肌球蛋白核心丝和一层肌球蛋白分子组成。肌球蛋白分子位于副肌球蛋白核心丝的两端，因此两端都具有极性。根据我们对天然粗肌丝中副肌球蛋白核心丝的观察，当在氯化钾溶液中短时间孵育时，它们的表面会出现规则的横纹，周期约为14.5纳米。这种周期性模式被认为代表了核心中副肌球蛋白分子的特殊排列，但在高浓度氯化钾溶液中长时间孵育时，周期性模式消失了，取而代之的是“贝尔-塞尔比网”模式。在来自4种“捕捉”肌（栉孔扇贝、牡蛎和蛤的闭壳肌以及贻贝的足丝牵缩肌）的4条副肌球蛋白核心丝中，这些“贝尔-塞尔比网”模式可方便地分为3种类型。牡蛎的“贝尔-塞尔比网”与栉孔扇贝的相似。从这4种肌肉中纯化得到的副肌球蛋白晶体显示出约72.5纳米的共同周期。在6%聚丙烯酰胺凝胶上对这4种副肌球蛋白进行SDS电泳，结果显示栉孔扇贝的副肌球蛋白分子量为104千道尔顿，牡蛎的为105千道尔顿，蛤的为103千道尔顿，贻贝的为105千道尔顿。
