Houghten R A, Li C H
Biochim Biophys Acta. 1976 Jul 19;439(1):240-9. doi: 10.1016/0005-2795(76)90179-3.
Three methionine-modified derivatives of ovine prolactin have been prepared: two by oxidation of the methionines by H2O2 to sulfoxide (partial and complete), and the third by complete alkylation of the metionines with iodoacetic acid to the carboxymethyl sulfonium salts. The derivatives were characterized by exclusion chromatography, amino acid composition, circular dichroism spectra, relative rates of digestion by trypsin, and biological activity. Partially oxidized prolactin, having four of its seven methionines oxidized, was very similar to the native hormone. The unmodified methionines in partially oxidized prolactin were found to be the residues at positions 36, 81 and 132. The prolactin derivatives in which all the methionines had been oxidized, or alkylated, showed major changes in all parameters examined. In addition, circular dichroism spectra indicated that complete modification of all the methionines in prolactin exposes the normally buried tryptophans.
两种是通过过氧化氢将甲硫氨酸氧化为亚砜（部分氧化和完全氧化），第三种是通过用碘乙酸将甲硫氨酸完全烷基化生成羧甲基锍盐。这些衍生物通过排阻色谱法、氨基酸组成、圆二色光谱、胰蛋白酶消化的相对速率以及生物活性进行表征。部分氧化的催乳素，其七个甲硫氨酸中有四个被氧化，与天然激素非常相似。发现部分氧化的催乳素中未修饰的甲硫氨酸是第36、81和132位的残基。所有甲硫氨酸都被氧化或烷基化的催乳素衍生物在所有检测参数上都显示出重大变化。此外，圆二色光谱表明，催乳素中所有甲硫氨酸的完全修饰会使通常埋藏的色氨酸暴露出来。
