Hayes M L, Castellino F J
J Biol Chem. 1979 Sep 25;254(18):8777-80.
The preceding two manuscripts in this issue (Hayes, M. L., and Castellino, F. J. (1979) J. Biol. Chem. 254, 8768-8771, 8772-8776) describe the isolation and characterization of glycopeptides from human plasminogen affinity chromatography variants 1 and 2. Plasminogen variant 1 contains an asparagine288-based branched carbohydrate structure, which has been established in the immediately preceding manuscript. This structure is absent in variant 2. Plasminogen variants 1 and 2 contain a threonine-based glycoconjugate. This latter structure has been established by combination of methylation data, glycosidase digestions, periodate oxidations, and Smith degradations of the beta-eliminated reduced oligosaccharides. One glycopeptide unit, isolated from both plasminogen variants 1 (1D) and 2 (2D) possessed the following structure: Sia alpha 2 yields 3Gal beta 1 yields 3GalNAc-Thr. The threonine was found to be residue 345 in the Glu-plasminogen sequence. Another glycopeptide unit was also found to be present, in lower yields in both variants 1 (1E) and 2 (2E). The structure of this unit was: Sia alpha 2 yields 3Gal beta1 yields 3GalNAc-Thr. : formula: (see text), alpha 2,6 Sia. Again Thr 345 was the glycosylated amino acid. The amino acid sequence around the glycosylated threonine was found to be NH2-Ala.Pro.Thr(CHO).Ala.Pro.Pro.Glu.
本期的前两篇稿件（海斯，M. L.，和卡斯泰利诺，F. J.（1979年）《生物化学杂志》254卷，8768 - 8771页，8772 - 8776页）描述了从人纤溶酶原亲和层析变体1和2中分离和鉴定糖肽的过程。纤溶酶原变体1含有基于天冬酰胺288的分支碳水化合物结构，这已在上一篇稿件中得到证实。变体2中不存在这种结构。纤溶酶原变体1和2含有基于苏氨酸的糖缀合物。后一种结构是通过对β-消除还原寡糖的甲基化数据、糖苷酶消化、高碘酸盐氧化和史密斯降解进行综合分析确定的。从纤溶酶原变体1（1D）和2（2D）中分离出的一个糖肽单元具有以下结构：唾液酸α2→3半乳糖β1→3N-乙酰半乳糖胺-苏氨酸。发现苏氨酸是谷氨酸-纤溶酶原序列中的345位残基。还发现另一个糖肽单元也存在于变体1（1E）和2（2E）中，但其产量较低。该单元的结构为：唾液酸α2→3半乳糖β1→3N-乙酰半乳糖胺-苏氨酸：化学式：（见正文），α2,6唾液酸。同样，苏氨酸345是糖基化氨基酸。发现糖基化苏氨酸周围的氨基酸序列为NH2-丙氨酸·脯氨酸·苏氨酸（CHO）·丙氨酸·脯氨酸·脯氨酸·谷氨酸。
