Misumi Y, Tanaka Y, Ikehara Y
Biochem Biophys Res Commun. 1983 Jul 29;114(2):729-36. doi: 10.1016/0006-291x(83)90841-0.
Biosynthesis, intracellular processing and secretion of the hetero-tetrameric (alpha 2 beta 2) glycoprotein, haptoglobin, were studied in primary cultured rat hepatocytes. The results obtained from pulse-chase experiments demonstrated that haptoglobin was initially synthesized as a larger precursor (pro-form), a single polypeptide chain comprising both the alpha- and beta-subunits, and immediately cleaved into subunits during intracellular transport, although about 8% of the newly synthesized haptoglobin was secreted as a pro-form. Monensin which impedes the secretory process at the Golgi complex blocked the complete glycosylation of beta-subunit but rather accelerated the conversion of the pro-form to subunits. These results indicate that the proteolytic processing of the haptoglobin precursor takes place at an early stage before the Golgi complex of the intracellular transport.
在原代培养的大鼠肝细胞中研究了异源四聚体（α2β2）糖蛋白触珠蛋白的生物合成、细胞内加工和分泌。脉冲追踪实验结果表明，触珠蛋白最初作为一种更大的前体（前体形式）合成，是一条包含α和β亚基的单多肽链，在细胞内运输过程中立即裂解为亚基，尽管约8%新合成的触珠蛋白以前体形式分泌。莫能菌素可阻碍高尔基体的分泌过程，它阻断了β亚基的完全糖基化，但加速了前体形式向亚基的转化。这些结果表明，触珠蛋白前体的蛋白水解加工发生在细胞内运输的高尔基体之前的早期阶段。
