Arias I M, Kyte J
Biochim Biophys Acta. 1979 Oct 19;557(1):170-8. doi: 10.1016/0005-2736(79)90099-3.
We have examined the hypothesis that hydrophilic portions of membrane-bound proteins which lie on either side of the phospholipid bilayer may be degraded at a different rate than are the hydrophobic portions of membrane proteins which are within the bilayer. Plasma membrane fractions from cells of the Maden-Darby canine kidney cell line and rat liver were digested with papain and pronase to cleave a mixture of peptides which is enriched in hydrophilic amino acids. It is proposed that these peptides are derived from regions of membrane-bound proteins which lie outside the bilayer. The residual particulate protein is enriched in hydropholic amino acids and presumably contains the portion of membrane-bound proteins which are in direct contact with the bilayer. A double-isotope method was used to assess the relative degradation rates of these two protein fractions. There was no measurable difference in protein degradation rates between the two fractions and the initial plasma membranes. These results suggest that the intramolecular heterogeneity which results from insertion of membrane-bound proteins into a bilayer is not a factor in their degradation.
位于磷脂双分子层两侧的膜结合蛋白的亲水性部分，其降解速率可能与处于双分子层内的膜蛋白的疏水性部分不同。用木瓜蛋白酶和链霉蛋白酶消化来自犬肾Maden-Darby细胞系和大鼠肝脏细胞的质膜组分，以切割富含亲水性氨基酸的肽混合物。据推测，这些肽源自双分子层之外的膜结合蛋白区域。残留的颗粒状蛋白富含疏水性氨基酸，大概包含与双分子层直接接触的膜结合蛋白部分。采用双同位素法评估这两种蛋白质组分的相对降解速率。这两个组分与初始质膜之间的蛋白质降解速率没有可测量的差异。这些结果表明，膜结合蛋白插入双分子层所导致的分子内异质性不是其降解的一个因素。
