Raviv O, Heller H, Hershko A
Biochem Biophys Res Commun. 1987 Jun 15;145(2):658-65. doi: 10.1016/0006-291x(87)91015-1.
Previous studies have shown that the activity of the ubiquitin-mediated proteolytic system declines markedly following reticulocyte maturation, but the specific alterations responsible for this phenomenon have not been defined. We find that the rate of ATP-dependent degradation of 125I-albumin is reduced 20-fold in lysates of rabbit erythrocytes, as compared to reticulocyte lysates. The activity of the proteolytic system in erythrocyte extracts can be restored by supplementation with components of the ubiquitin-protein ligase system purified from reticulocytes by affinity chromatography. These components are the ubiquitin-carrier protein E2, the activity of which is nearly completely absent, and the ligase E3, the activity of which is partially reduced in erythrocytes. Erythrocyte extracts contain other ligases which attach a single, or a few ubiquitin molecules to proteins; these products are different from the multi-ubiquitin derivatives which are formed by the ligase system of protein breakdown. Mature red cells may thus serve to distinguish between different ubiquitin-protein ligase systems with presumably different functions.
先前的研究表明，泛素介导的蛋白水解系统的活性在网织红细胞成熟后会显著下降，但导致这种现象的具体变化尚未明确。我们发现，与网织红细胞裂解物相比，兔红细胞裂解物中125I-白蛋白的ATP依赖性降解速率降低了20倍。通过补充经亲和层析从网织红细胞中纯化的泛素-蛋白连接酶系统的组分，可恢复红细胞提取物中蛋白水解系统的活性。这些组分是泛素载体蛋白E2，其活性几乎完全缺失，以及连接酶E3，其活性在红细胞中部分降低。红细胞提取物含有其他连接酶，这些连接酶将单个或少数泛素分子连接到蛋白质上；这些产物不同于由蛋白质分解连接酶系统形成的多泛素衍生物。因此，成熟红细胞可能有助于区分具有不同功能的不同泛素-蛋白连接酶系统。
