Weidner E
J Cell Biol. 1976 Oct;71(1):23-34. doi: 10.1083/jcb.71.1.23.
The extrusion apparatus of the microsporidian parasitic protozoan Nosema michaelis discharges an invasion (or polar) tube with a velocity suitalbe for piercing cells and injecting infective sporoplasm. The tube is composed of a polar tube protein (PTP) which consists of a single, low molecular weight polypeptide slightly smaller than chymotrypsinogen-A. Assembled PTP tubes resist dissociation in sodium dodecyl sulfate and brief exposures in media at extreme ends of the pH range; however, the tubes are reduced by mercaptoethanol and dithiothreitol. When acidified, mercaptoethanol-reduced PTP self-assembles into plastic, two-dimensional monolayers. Dithiothreitol-reduced PTP will not reassemble when acidified. Evidence is presented which indicates that PTP is assembled as a tube within the spore; that the ejected tube has plasticity during sporoplasm passage; and, finally, that the subunits within the tube polymer are bound together, in part, by interprotein disulfide linkages.
微小孢子虫寄生原生动物米氏 Nosema 的挤压装置以适合刺穿细胞并注入感染性孢子质的速度排出侵入（或极）管。该管由极管蛋白（PTP）组成，PTP 由一种单一的低分子量多肽组成，略小于胰凝乳蛋白酶原 -A。组装好的 PTP 管在十二烷基硫酸钠中抗解离，并且在 pH 范围两端的培养基中短暂暴露也不会解离；然而，这些管会被巯基乙醇和二硫苏糖醇还原。酸化时，经巯基乙醇还原的 PTP 会自组装成可塑性的二维单层。经二硫苏糖醇还原的 PTP 在酸化时不会重新组装。有证据表明，PTP 在孢子内组装成管；在孢子质通过期间，射出的管具有可塑性；最后，管聚合物内的亚基部分地通过蛋白质间二硫键结合在一起。
