Póvoa G, Enberg G, Jörnvall H, Hall K
Eur J Biochem. 1984 Oct 15;144(2):199-204. doi: 10.1111/j.1432-1033.1984.tb08449.x.
Human amniotic fluid is rich in a binding protein for somatomedins. This binding protein competes with human placenta membranes for labelled somatomedin A. Consequently, the placenta radioreceptorassay for somatomedin can be used for detection of the binding protein. The protein was isolated from human amniotic fluid by a three-step procedure: First, stepwise ammonium sulphate precipitation; second, hydrophobic chromatography (phenyl-Sepharose); and third, anion-exchange chromatography (fast protein liquid chromatography). The total recovery of binding protein calculated with the placenta radioreceptorassay was 50%. Polyacrylamide gel electrophoresis under native and denaturating conditions of the isolated protein disclosed a single band. The relative molecular mass was 35000, determined by exclusion chromatography, and 32000 under denaturating conditions in sodium dodecyl sulphate/polyacrylamide gel electrophoresis. The isoelectric point was 4.3 according to chromatofocusing and the amino acid composition also disclosed a high content of acidic/amidated residues. The N-terminal amino acid sequence was Ala-Pro-Trp-Gln-Cys-Ala-Pro-Cys-Ser-Ala.
人羊水富含生长调节素结合蛋白。这种结合蛋白能与人胎盘膜竞争标记的生长调节素A。因此，生长调节素的胎盘放射受体测定法可用于检测该结合蛋白。通过三步法从人羊水中分离出该蛋白：第一步，硫酸铵分步沉淀；第二步，疏水层析（苯基琼脂糖）；第三步，阴离子交换层析（快速蛋白质液相层析）。用胎盘放射受体测定法计算，结合蛋白的总回收率为50%。在天然和变性条件下对分离出的蛋白进行聚丙烯酰胺凝胶电泳，结果显示为单一一条带。通过排阻层析测定，其相对分子质量为35000，在十二烷基硫酸钠/聚丙烯酰胺凝胶电泳的变性条件下为32000。根据层析聚焦法，其等电点为4.3，氨基酸组成也显示酸性/酰胺化残基含量很高。其N端氨基酸序列为Ala-Pro-Trp-Gln-Cys-Ala-Pro-Cys-Ser-Ala。
