Necessary P C, Andersen T T, Ebner K E
Mol Cell Endocrinol. 1985 Mar;39(3):247-54. doi: 10.1016/0303-7207(85)90068-1.
The disulfide bonds of two lactogenic hormones, ovine prolactin (oPRL) and human growth hormone (hGH), were reduced with dithiothreitol under denaturing conditions and alkylated with iodoacetic acid. The modified hormones were assayed for their ability to bind the plasma membrane-bound receptor for lactogenic hormone found in the rabbit mammary gland. S-Carboxymethylated ovine prolactin (SCM-oPRL) with all six cysteine residues modified had a nearly 300-fold decrease in binding as compared to native oPRL in a competitive binding assay using [125I]ovine prolactin. The S-carboxymethylated human growth hormone (SCM-hGH) had all four of its cysteine residues modified. It showed only a slightly reduced ability to bind the rabbit mammary gland prolactin receptor in a competitive binding assay with [125I]ovine prolactin. The two modified hormones were assayed for their ability to stimulate proliferation of the lactogen-dependent Nb 2 lymphoma cell line. SCM-oPRL required concentrations greater than 1 X 10(5) that of native oPRL to stimulate 50% of the maximum cell growth. SCM-hGH retained a significant amount of its ability to stimulate the Nb 2 lymphoma cells.
在变性条件下，用二硫苏糖醇还原两种催乳激素，即绵羊催乳素（oPRL）和人生长激素（hGH）的二硫键，并用碘乙酸进行烷基化。检测修饰后的激素与兔乳腺中发现的催乳激素的质膜结合受体结合的能力。在使用[125I]绵羊催乳素的竞争性结合试验中，与天然oPRL相比，所有六个半胱氨酸残基均被修饰的S-羧甲基化绵羊催乳素（SCM-oPRL）的结合能力下降了近300倍。S-羧甲基化人生长激素（SCM-hGH）的四个半胱氨酸残基均被修饰。在使用[125I]绵羊催乳素的竞争性结合试验中，它与兔乳腺催乳素受体结合的能力仅略有下降。检测这两种修饰后的激素刺激催乳素依赖性Nb 2淋巴瘤细胞系增殖的能力。SCM-oPRL刺激50%最大细胞生长所需的浓度比天然oPRL高1×10（5）倍以上。SCM-hGH仍保留大量刺激Nb 2淋巴瘤细胞的能力。
