Burton-Wurster N, Lust G
James A. Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853.
Arch Biochem Biophys. 1993 Nov 1;306(2):309-20. doi: 10.1006/abbi.1993.1517.
Fibronectin heterogeneity is, in part, the result of post-translational modifications. In these experiments, cartilage fibronectins were purified by anion exchange chromatography, followed by gelatin affinity chromatography or immunoprecipitation, and, finally, sodium dodecyl sulfate--polyacrylamide gel electrophoresis (NaDodSO4 PAGE). A substantial, although variable, portion of the fibronectins from canine and equine cartilages of all ages required salt concentrations from 0.2 to 1.0 M for elution from DEAE-cellulose. This was in contrast to plasma fibronectin which eluted with 0.1 M NaCl, but these results were consistent with observations made on human cartilage by Brown and Jones (1990 J. Rheumatol. 17, 65-72). When cartilage explants were incubated with Na2 35SO4=, the cartilage fibronectins were sulfated and the fibronectins which eluted with high salt contained from 5- to 50-fold more radiosulfate than the fibronectins which eluted with 0.1 M NaCl. A fraction of the 35SO4= which copurified with the cartilage fibronectin and comigrated with it in NaDodSO4-PAGE could be removed by digestion with chondroitinase ABC. This suggested that a percentage of cartilage fibronectins are covalently linked to a chondroitin sulfate or dermatan sulfate chain and thus might also appropriately be called proteoglycans. Alternatively, there is a proteoglycan which binds so tightly to fibronectin that separation is not achieved even in the presence of urea, sodium dodecyl sulfate, and mercaptoethanol.
纤连蛋白的异质性部分是翻译后修饰的结果。在这些实验中，软骨纤连蛋白通过阴离子交换色谱法进行纯化，随后进行明胶亲和色谱法或免疫沉淀，最后进行十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）。来自所有年龄段犬类和马类软骨的纤连蛋白，有相当一部分（尽管存在差异）需要0.2至1.0 M的盐浓度才能从DEAE-纤维素上洗脱下来。这与血浆纤连蛋白在0.1 M NaCl条件下洗脱的情况形成对比，但这些结果与Brown和Jones（1990年，《风湿病学杂志》17卷，65 - 72页）对人类软骨的观察结果一致。当软骨外植体与Na₂³⁵SO₄孵育时，软骨纤连蛋白会发生硫酸化，用高盐洗脱的纤连蛋白所含的放射性硫酸盐比用0.1 M NaCl洗脱的纤连蛋白多5至50倍。与软骨纤连蛋白共纯化并在SDS-PAGE中与其迁移的一部分³⁵SO₄可以通过软骨素酶ABC消化去除。这表明一定比例的软骨纤连蛋白与硫酸软骨素或硫酸皮肤素链共价连接，因此也可能恰当地被称为蛋白聚糖。或者，存在一种与纤连蛋白紧密结合的蛋白聚糖，即使在有尿素、十二烷基硫酸钠和巯基乙醇的情况下也无法实现分离。
