ASSEMBLY OF ATPASE PROTEIN IN SARCOPLASMIC-RETICULUM MEMBRANES
ASSEMBLY OF ATPASE PROTEIN IN SARCOPLASMIC-RETICULUM MEMBRANES
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DOI：
10.1016/s0006-3495(76)85725-6
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发表时间：
1976-01-01
影响因子：
3.4
通讯作者：
INESI, G
中科院分区：
文献类型：
--
作者：
SCALES, D;INESI, G
本文用三种电镜标本制备技术研究了兔骨骼肌肌浆网（SR）膜ATP酶多肽链的掺入。观察正常囊泡和暴露于胰蛋白酶的囊泡，已知胰蛋白酶切割ATP酶蛋白并以可预测的方式改变囊泡的超微结构。冷冻断裂复制品揭示了典型的90埃。在凹（PF）面上的颗粒的密度为5730 ± 0.5。520/μ m2。另一方面，负染色和深蚀刻制剂显示外投影，这是缺乏酪氨酸蛋白酶孵育囊泡。蚀刻的标本提供了第一次顶视图的囊泡在没有任何染色。这些视图显示PS [外部]表面上的外部投影，密度为21，000 ±。3900/μ m2，该值几乎接近基于蛋白质和膜面积测定计算的ATP酶多肽链的密度（106，000 MW）。该值比90埃的密度高3-4倍。在凹状断裂面上的颗粒。由于外部投影和90-A。颗粒与ATP酶蛋白质相同，ATP酶多肽链可能是两亲性分子，其极性末端单独突出为囊泡表面的外部突起，而疏水性末端表现为90 °。在凹状断裂面上的颗粒。外部突起的密度和90-A的密度之间的差异是由外部突起的密度和90-A的密度之间的差异引起的。颗粒的形成可以归因于多肽链可变地渗透到膜双层中，或者归因于含有3-4个疏水末端并表现为单个90-Δ G的寡聚体的形成。粒子每条ATP酶链与20-30个磷脂分子形成复合物。剩余的磷脂（约总SR磷脂的70%）占膜体积的不到一半。SR膜的外叶主要由ATP酶脂蛋白复合物组成，内叶主要是磷脂单层。
Three specimen preparation techniques for electron microscopy were used to investigate the incorporation of the ATPase polypeptide chains in the membranes of fragmented sarcoplasmic reticulum (SR) obtained from rabbit skeletal muscle. Observations were made of both normal vesicles and vesicles exposed to trypsin, which is known to cleave the ATPase protein and to alter the ultrastructure of the vesicles in predictable ways. Freeze-fracture replicas reveal the typical 90-.ANG. particles on the concave (PF) faces with a density of 5730 .+-. 520/.mu.m2. On the other hand both negatively stained and deeply etched preparations display outer projections, which are absent on tyrpsin-incubated vesicles. The etched specimens afford for the first time top views of the vesicles in the absence of any stain. These views reveal outer projections on the PS [external] surface with a density of 21,000 .+-. 3900/.mu.m2, a value nearly approximating the density of the ATPase polypeptide chains (106,000 MW) calculated on the basis of protein and membrane area determinations. This value is 3-4 times higher than that found for the density of the 90-.ANG. particles on the concave fracture faces. Since both outer projections and 90-.ANG. particles are identified with the ATPase protein, the ATPase polypeptide chains are probably amphiphilic molecules, with polar ends protruding individually as outer projections on the surface of the vesicles, and hydrophobic ends appearing as 90-.ANG. particles on the concave fracture faces. The discrepancy between the densities of the outer projections and the 90-.ANG. particles may be attributed either to variable penetration of the polypeptide chains into the membrane bilayer, or to formation of oligomers containing 3-4 hydrophobic ends and appearing as single 90-.ANG. particles. Each ATPase chain forms a complex with 20-30 phospholipid molecules. The remaining phospholipids (.apprx. 70% of the total SR phospholipids) account for less than half the membrane volume. The outer leaflet of the SR membrane is prevalently composed of the ATPase lipoprotein complex, and the inner leaflet is mostly a phospholipid monolayer.