Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, T6G 2P5, Canada.
J Dairy Res. 2020 Aug;87(3):364-367. doi: 10.1017/S0022029920000783. Epub 2020 Sep 4.
Bovine κ-casein glycomacropeptide (GMP) is a sialic acid containing glycopeptide having many biological activities. The study described in this research communication was undertaken to determine whether sialic acid rich glycopeptide can be produced from GMP by proteinase treatment. A sample of GMP was hydrolyzed with papain, and the obtained hydrolysate was chromatographed on a column of diethylaminoethyl-Sephacel to obtain a glycopeptide fraction (GPF). This product accounted for average 48.1% dry weight of GMP or 81.1% total recovered sialic acid from GMP. The content of sialic acid (expressed as % dry weight) was 1.7 times higher in GPF (22.6) than in unhydrolyzed GMP (13.4). Major differences in amino acid composition between GPF and GMP were found in the contents (mol%) of: lysine (<1 and 4.5, respectively), serine (20.3 and 10.3, approximately twice higher in GPF), asparagine/aspartic acid and isoleucine. The contents of the last two amino acids were approximately twice lower in GPF. On gel filtration chromatography with Sephacryl S-100, GMP was eluted as a single peak with elution volume similar to that of dimeric β-lactoglobulin (36.6 kDa) whereas GPF was eluted in two peaks both with elution volumes greater than that of α-lactalbumin (14.2 kDa). These peak fractions containing high (fraction I) and low (fraction II) molecular size glycopeptides gave different sialic acid to peptide ratio, which was 1.7 times higher in fraction I than in fraction II. Results of size exclusion HPLC on Superdex-75 were consistent with those of gel filtlation chromatography. On cellulose acetate electrophoresis, the mobility of GPF relative to that of GMP as 1.0 was found to average 1.2, suggesting a higher negative charge density in GPF than in GMP. It was concluded that papain digestion of GMP is an efficient method to produce glycopeptide with high sialic acid content.
牛κ-酪蛋白糖巨肽（GMP）是一种含有唾液酸的糖肽，具有多种生物活性。本研究通讯中描述的研究旨在确定通过蛋白酶处理是否可以从 GMP 生产出富含唾液酸的糖肽。将 GMP 样品用木瓜蛋白酶水解，然后将得到的水解产物在 DEAE-葡聚糖 Sephacel 柱上进行色谱分离，得到糖肽级分（GPF）。该产品占 GMP 干重的平均 48.1%或 GMP 总回收唾液酸的 81.1%。GPF 中的唾液酸含量（以干重表示）为 1.7 倍，高于未水解的 GMP（13.4%）。GPF 与 GMP 在氨基酸组成上的主要差异在于：赖氨酸（分别为<1 和 4.5，GPF 中分别为 4.5 和 4.5）、丝氨酸（20.3 和 10.3，GPF 中约为 2 倍）、天冬酰胺/天冬氨酸和异亮氨酸。后两种氨基酸的含量在 GPF 中约为 2 倍。在 Sephacryl S-100 凝胶过滤色谱中，GMP 洗脱为单个峰，洗脱体积与二聚体β-乳球蛋白（36.6 kDa）相似，而 GPF 洗脱为两个峰，洗脱体积均大于α-乳白蛋白（14.2 kDa）。这两个峰的级分含有高（级分 I）和低（级分 II）分子量的糖肽，其唾液酸与肽的比值不同，级分 I 中的比值比级分 II 中的高 1.7 倍。Superdex-75 上的排阻 HPLC 结果与凝胶过滤色谱结果一致。在醋酸纤维素电泳中，GPF 相对于 GMP 的迁移率为 1.0，平均为 1.2，表明 GPF 的负电荷密度高于 GMP。研究结果表明，木瓜蛋白酶消化 GMP 是生产高唾液酸含量糖肽的有效方法。
