Jentjens T, Strous G J
Biochem J. 1985 May 15;228(1):227-32. doi: 10.1042/bj2280227.
The synthesis of the polypeptide backbone of mucus glycoproteins in rat stomach was studied. CsCl centrifugation of the homogenate of [3H]serine pulse-chase labelled stomach or mucosal scrapings showed that [3H]serine was mainly incorporated into molecules having a density identical to that of proteins and that only 8-12% was incorporated into macromolecules with the density of mucus glycoproteins. [3H]-Galactose, however, was almost exclusively incorporated into macromolecules with a density identical to that of mucus glycoproteins. Electrophoretic analysis of the CsCl fraction containing the mucus glycoprotein revealed that 78% of the [3H]serine-labelled macromolecules had an electrophoretic behaviour identical to that of mucus glycoproteins. Thus, only a small portion (about 6-10%) of incorporated [3H]serine was present in the backbone of the mucus glycoprotein. Translation in a wheat germ cell-free system of total RNA derived from both whole stomach and superficial mucosal scrapings, using either [35S]methionine or [35S]cysteine as radioactive amino acid, yielded a wide range of proteins. On sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, one major translation product of whole stomach RNA had an apparent Mr (43000) identical to that of rat pepsinogen. As this polypeptide could not be found amongst the translation products of RNA from scrapings it probably was pepsinogen. The present data provide strong evidence that the backbone polypeptide of mucus glycoproteins only accounts for a small part of the proteins synthesized by mucus-producing cells.
对大鼠胃黏液糖蛋白多肽主链的合成进行了研究。对用[³H]丝氨酸脉冲追踪标记的胃或黏膜刮片匀浆进行氯化铯离心，结果显示[³H]丝氨酸主要掺入密度与蛋白质相同的分子中，仅有8 - 12%掺入密度与黏液糖蛋白相同的大分子中。然而，[³H] - 半乳糖几乎完全掺入密度与黏液糖蛋白相同的大分子中。对含有黏液糖蛋白的氯化铯组分进行电泳分析表明，78%的[³H]丝氨酸标记的大分子具有与黏液糖蛋白相同的电泳行为。因此，掺入的[³H]丝氨酸中只有一小部分（约6 - 10%）存在于黏液糖蛋白的主链中。使用[³⁵S]甲硫氨酸或[³⁵S]半胱氨酸作为放射性氨基酸，在来自整个胃和表层黏膜刮片的总RNA的小麦胚无细胞系统中进行翻译，产生了多种蛋白质。在十二烷基硫酸钠/聚丙烯酰胺凝胶电泳上，整个胃RNA的一个主要翻译产物的表观分子量（43000）与大鼠胃蛋白酶原相同。由于在刮片RNA的翻译产物中未发现这种多肽，它可能就是胃蛋白酶原。目前的数据提供了有力证据，表明黏液糖蛋白的主链多肽仅占黏液产生细胞合成的蛋白质的一小部分。
