Kramer K J, Dunn P E, Peterson R C, Seballos H L, Sanburg L L, Law J H
J Biol Chem. 1976 Aug 25;251(16):4979-85.
The larval hemolymph of the tobacco hornworm, Manduca sexta, contains a carrier protein that binds specifically and with high affinity the juvenile hormone, an important regulator of insect development. This protein serves to transport the hormone and to protect it from the action of degradative enzymes during early larval stages. Using hemolymph from the last larval stage, we have isolated a pure carrier protein using acetone precipitation, gel filtration, ion exchange chromatography, and preparative isoelectric focusing. Gel filtration, polyacrylamide gel electrophoresis in sodium dodecyl sulfate, and equilibrium ultracentrifugation established that the carrier protein is a single chain polypeptide of approximately 28,000 daltons. The amino acid composition is unexceptional, and no evidence for hexosamine has been obtained. An ion exchange filter disc assay method was used to determine the formation of the complex between the carrier protein and isotopically labeled juvenile hormone. With this technique it was shown that each carrier protein binds one hormone molecule with a dissociation constant of 4.4 +/- 0.2 X 10(-7) M at 0 degrees.
烟草天蛾（Manduca sexta）幼虫的血淋巴中含有一种载体蛋白，它能特异性且高亲和力地结合保幼激素，保幼激素是昆虫发育的重要调节因子。这种蛋白在幼虫早期阶段起到运输激素并保护其免受降解酶作用的功能。我们利用末龄幼虫的血淋巴，通过丙酮沉淀、凝胶过滤、离子交换色谱和制备性等电聚焦等方法分离出了一种纯的载体蛋白。凝胶过滤、十二烷基硫酸钠聚丙烯酰胺凝胶电泳和平衡超速离心表明，该载体蛋白是一条约28,000道尔顿的单链多肽。其氨基酸组成并无异常，也未获得存在己糖胺的证据。采用离子交换滤膜分析方法来测定载体蛋白与同位素标记的保幼激素之间复合物的形成。利用该技术表明，每个载体蛋白在0摄氏度时以4.4±0.2×10⁻⁷ M的解离常数结合一个激素分子。
