Podlubnaya Z A, Freydina N A, Lednev V V
Institute of Biological Physics, USSR Academy of Sciences, Moscow Region.
Gen Physiol Biophys. 1990 Jun;9(3):301-10.
We examined the axial repeats in electron micrographs of three types of negatively stained paracrystals (two tactoid- and one sheet-like type) of rabbit light meromyosin (LMM) and its complex with C-protein characterized previously by similar axial period of about 43.0 nm. Assuming for the axial repeat in type II tactoids the value of 42.93 +/- 0.05 nm as it was determined by X-ray diffraction technique (Yagi and Offer 1981), we found average axial repeats in type I tactoid and in sheet-like paracrystal of 42.93 +/- 0.75 nm and 43.50 +/- 0.62 nm respectively. Analyzing the micrographs where the two types paracrystals are located side-by-side we determined rather accurately the average ratio of axial repeat in sheet-like paracrystal to that in type I tactoid (1.013 +/- 0.002). Taking 42.93 nm as the axial repeat in type I tactoid, the axial repeat in sheet-like paracrystal was found to be 43.50 +/- 0.08 nm. C-protein binds to LMM with the period of the underlying LMM paracrystals and independently of the value of their axial repeats. Two different axial repeats (42.9 nm and 43.5 nm) revealed for LMM paracrystals in this study precisely coincide with the average repeat periods of myosin crossbridges along the thick filaments found for different physiological states of skeletal muscles (Lednev and Kornev 1987). Molecular basis for the appearance of two structural states in LMM paracrystals and in the shafts of thick filaments are discussed.
我们检查了三种类型的负染副晶体（两种类 tactoid 型和一种片状型）的电子显微照片中的轴向重复，这三种副晶体分别是兔轻酶解肌球蛋白（LMM）及其与 C 蛋白的复合物，之前已通过约 43.0 nm 的相似轴向周期进行了表征。假设 II 型类 tactoid 中的轴向重复值为通过 X 射线衍射技术测定的 42.93±0.05 nm（Yagi 和 Offer，1981），我们发现 I 型类 tactoid 和片状副晶体中的平均轴向重复分别为 42.93±0.75 nm 和 43.50±0.62 nm。通过分析两种副晶体并排排列的显微照片，我们相当准确地确定了片状副晶体与 I 型类 tactoid 中轴向重复的平均比率（1.013±0.002）。以 I 型类 tactoid 中的轴向重复为 42.93 nm，发现片状副晶体中的轴向重复为 43.50±0.08 nm。C 蛋白以底层 LMM 副晶体的周期与 LMM 结合，且与它们轴向重复的值无关。本研究中揭示的 LMM 副晶体的两种不同轴向重复（42.9 nm 和 43.5 nm）与在骨骼肌不同生理状态下发现的肌球蛋白横桥沿粗肌丝的平均重复周期精确吻合（Lednev 和 Kornev，1987）。本文讨论了 LMM 副晶体和粗肌丝杆状部分中两种结构状态出现的分子基础。
