Patzelt C, Weber B
EMBO J. 1986 Sep;5(9):2103-8. doi: 10.1002/j.1460-2075.1986.tb04472.x.
Proglucagon from rat islets is identified as a glycoprotein by its binding to soybean lectin and by the biosynthetic incorporation of [14C]galactosamine. Glycosylation can be demonstrated for both forms of proglucagon, i.e. the primary translation product which is detectable as early as 30 s after incubation of isolated islets with radioactive amino acids (proglucagon a), and its conversion product of slightly higher electrophoretic mobility which is formed after 5-10 min of incubation (proglucagon b). This glycosylation is determined to be of the O-glycosidic type by the following criteria: rat proglucagon has previously been shown to lack an acceptor sequence for N-glycosidic linkage of sugars, the sugar bond in rat proglucagon is labile under mild alkaline conditions, glycosylated serine is demonstrated in proteolytic lysates of both the early and the late form of this prohormone. O-glycosidic linkage of sugars has not been reported for other prohormones. Its early formation and the apparent absence of N-glycosidically bound sugars in proglucagon give evidence for an unusual type of protein glycosylation.
通过大鼠胰岛中胰高血糖素原与大豆凝集素的结合以及[14C]半乳糖胺的生物合成掺入，可将其鉴定为一种糖蛋白。两种形式的胰高血糖素原均可显示出糖基化，即最早在分离的胰岛与放射性氨基酸孵育30秒后即可检测到的初级翻译产物（胰高血糖素原a），以及在孵育5-10分钟后形成的电泳迁移率略高的转化产物（胰高血糖素原b）。根据以下标准确定这种糖基化为O-糖苷型：先前已证明大鼠胰高血糖素原缺乏糖的N-糖苷键连接的受体序列，大鼠胰高血糖素原中的糖键在温和碱性条件下不稳定，在该前体激素早期和晚期形式的蛋白水解裂解物中均显示出糖基化的丝氨酸。其他前体激素尚未报道糖的O-糖苷键连接。其早期形成以及胰高血糖素原中明显不存在N-糖苷键结合的糖，为一种不寻常的蛋白质糖基化类型提供了证据。
