Mano T, Chou J Y
J Biol Chem. 1982 May 25;257(10):5827-30.
Pulse and pulse-chase experiments demonstrated that a heterogeneous polypeptide with an apparent Mr = 68,000 was the first intracellular anti-alpha-fetoprotein (AFP)-precipitable polypeptide synthesized by rat Mc-A-RH-7777 hepatoma cells. The 68,000-dalton polypeptide may consist of polypeptides with apparent molecular weights ranging from 68,000 to 70,000. It was the precursor of two intracellular anti-AFP-precipitable polypeptides of 69,000 and 73,000 apparent molecular weight. The latter were secreted into the medium without further processing. The anti-AFP-precipitable polypeptides in both cells and medium incorporated [3H]glucosamine, indicating that these polypeptides are at least partially glycosylated. The 68,000-dalton polypeptide in cells was bound mostly to concanavalin A-Sepharose, whereas the 69,000-dalton polypeptide was entirely unbound. The 73,000-dalton polypeptide consisted of concanavalin A-bound and -unbound variants. Tunicamycin completely abolished the uptake of [3H]glucosamine into anti-AFT-precipitable polypeptides in both cells and medium, and the resulting polypeptide of apparent Mr = 66,000 did not bind to concanavalin A-Sepharose. Tunicamycin did not affect the synthesis or secretion of AFP by hepatoma cells.
脉冲追踪实验表明，一种表观分子量为68,000的异质多肽是大鼠Mc-A-RH-7777肝癌细胞合成的第一种细胞内抗甲胎蛋白（AFP）可沉淀多肽。这种68,000道尔顿的多肽可能由表观分子量在68,000至70,000之间的多肽组成。它是两种表观分子量为69,000和73,000的细胞内抗AFP可沉淀多肽的前体。后者未经进一步加工就分泌到培养基中。细胞和培养基中的抗AFP可沉淀多肽都掺入了[3H]葡糖胺，表明这些多肽至少部分被糖基化。细胞中的68,000道尔顿多肽大多与伴刀豆球蛋白A-琼脂糖结合，而69,000道尔顿的多肽则完全不结合。73,000道尔顿的多肽由伴刀豆球蛋白A结合型和非结合型变体组成。衣霉素完全消除了细胞和培养基中[3H]葡糖胺掺入抗AFP可沉淀多肽的过程，产生的表观分子量为66,000的多肽不与伴刀豆球蛋白A-琼脂糖结合。衣霉素不影响肝癌细胞中AFP的合成或分泌。
