Cöster L, Hernnäs J, Malmström A
Department of Physiological Chemistry, Lund University, Sweden.
Biochem J. 1991 Jun 1;276 ( Pt 2)(Pt 2):533-9. doi: 10.1042/bj2760533.
Incubation of cultured fibroblasts with p-nitrophenyl beta-D-xyloside resulted in a concentration-dependent increase in galactosaminoglycan synthesis. At low concentration of added xyloside large and small radiolabelled proteoglycans and xyloside-bound polysaccharides were recovered from the medium, whereas at high concentrations only xyloside-bound polysaccharides were found. In the cell layer proteoglycans and xyloside-bound polysaccharides were found at all concentrations tested. Only galactosaminoglycan chains were polymerized on the xyloside primer. At low concentrations of added xyloside the structure of the galactosaminoglycans formed on the xyloside was similar to that of the small dermatan sulphate proteoglycan, i.e. mainly composed of L-iduronic acid-containing 4-sulphated disaccharides. With increasing concentration of added xyloside the co-polymeric structure of the small dermatan sulphate proteoglycan and the xyloside-bound polysaccharide was changed to contain a larger proportion of D-glucuronosyl residues with only slight changes in the sulphation pattern. No structural change in the polysaccharide chains of the large glucuronic acid-rich proteoglycans occurred. At 1 mM-xyloside, where no proteoglycans were formed, the polysaccharide was shorter and composed mainly of D-glucuronosyl-containing disaccharides with a ratio of 4-sulphate to 6-sulphate substituents of 1:2. This is similar to the structure of the large glucuronic acid-rich proteoglycan synthesized by these cells. Thus the main difference induced by the xyloside treatment was changed polymer modification at high xyloside concentrations. The specific activities of the polymer-modifying enzymes, uronosyl C-5-epimerase and 4-sulphotransferase, were therefore measured and found to be decreased by 30-50% in fibroblasts treated with high xyloside concentrations. It is suggested that the protein core is of importance for regulating the activity of the polymer-modifying enzymes.
用对硝基苯基β-D-木糖苷培养成纤维细胞，结果半乳糖胺聚糖合成呈浓度依赖性增加。在添加低浓度木糖苷时，从培养基中回收了大小不同的放射性标记蛋白聚糖和与木糖苷结合的多糖，而在高浓度时，仅发现了与木糖苷结合的多糖。在所有测试浓度下，在细胞层中均发现了蛋白聚糖和与木糖苷结合的多糖。只有半乳糖胺聚糖链在木糖苷引物上聚合。在添加低浓度木糖苷时，在木糖苷上形成的半乳糖胺聚糖的结构类似于小硫酸皮肤素蛋白聚糖的结构，即主要由含L-艾杜糖醛酸的4-硫酸化二糖组成。随着添加木糖苷浓度的增加，小硫酸皮肤素蛋白聚糖和与木糖苷结合的多糖的共聚结构发生变化，含有更大比例的D-葡萄糖醛酸残基，硫酸化模式仅有轻微变化。富含葡萄糖醛酸的大蛋白聚糖的多糖链未发生结构变化。在1 mM木糖苷时，未形成蛋白聚糖，多糖较短，主要由含D-葡萄糖醛酸的二糖组成，4-硫酸盐与6-硫酸盐取代基的比例为1:2。这类似于这些细胞合成的富含葡萄糖醛酸的大蛋白聚糖的结构。因此，木糖苷处理引起的主要差异是在高木糖苷浓度下聚合物修饰的改变。因此，测定了聚合物修饰酶、糖醛酸C-5-表异构酶和4-硫酸转移酶的比活性，发现用高木糖苷浓度处理的成纤维细胞中这些酶的活性降低了30-50%。有人提出，蛋白质核心对于调节聚合物修饰酶的活性很重要。
