Rinaldi R A, Hrebenda B
J Cell Biol. 1975 Jul;66(1):193-8. doi: 10.1083/jcb.66.1.193.
Actin and myosin filaments as a foundation of contractile systems are well established from ameba to man (3). Wolpert et al. (19) isolated by differential centrifugation from Amoeba proteus a motile fraction composed of filaments which moved upon the addition of ATP. Actin filaments are found in amebas (1, 12, 13) which react with vertebrate heavy meromyosin (HMM), forming arrowhead complexes as vertebrate actin (3, 9), and are prominent within the ectoplasmic tube where some of them are attached to the plasmalemma (1, 12). Thick and thin filaments possessing the morphological characteristics of myosin and actin have been obtained from isolated ameba cytoplasm (18, 19). In addition, there are filaments exhibiting ATPase activity in amebas which react with actin (12, 16, 17). However, giant ameba (Chaos-proteus) shapes are difficult to preserve, and the excellent contributions referred to above are limited by visible distortions occurring in the amebas (rounding up, pseudopods disappearing, and cellular organelles swelling) upon fixation. Achievement of normal ameboid shape in recent glycerination work (15) led us to attempt other electron microscope fixation techniques, resulting in a surprising preservation of A. proteus with a unique orientation of thick and thin filaments in the ectoplasmic region.
肌动蛋白丝和肌球蛋白丝作为收缩系统的基础，从变形虫到人类都已得到充分证实（3）。沃尔珀特等人（19）通过差速离心从大变形虫中分离出一个可运动部分，该部分由添加ATP后会移动的细丝组成。在变形虫中发现了肌动蛋白丝（1, 12, 13），它们与脊椎动物的重酶解肌球蛋白（HMM）发生反应，像脊椎动物肌动蛋白一样形成箭头状复合物（3, 9），并且在一些附着于质膜的外质管内很突出（1, 12）。从分离出的变形虫细胞质中已获得具有肌球蛋白和肌动蛋白形态特征的粗丝和细丝（18, 19）。此外，在变形虫中存在一些与肌动蛋白发生反应且具有ATP酶活性的细丝（12, 16, 17）。然而，巨型变形虫（大变形虫）的形态难以保存，上述出色的研究成果受到变形虫在固定时出现的明显变形（变圆、伪足消失和细胞器肿胀）的限制。近期甘油处理工作（15）中实现了正常的变形虫形态，这促使我们尝试其他电子显微镜固定技术，结果令人惊讶地保存了大变形虫，其外质区域的粗丝和细丝具有独特的排列方向。
