Houghten R A, Li C H
Eur J Biochem. 1977 Jul 1;77(1):119-23. doi: 10.1111/j.1432-1033.1977.tb11649.x.
Treatment of human choriomammotropin with hydrogen peroxide in the absence of denaturant was found to oxidize five of its six methionine residues to sulfoxide; the residue not oxidized was found to be methionine-170. This derivative was identical to the native hormone by exclusion chromatography, circular dichroism spectra, and rate of tryptic digestion, but suffered a very substantial drop in biological activity. In the presence of 8 M urea all of the methionines could be oxidized with hydrogen peroxide or alkylated with iodoacetic acid. The physical properties of these completely methionine-modified derivatives were significantly changed and biological activity had again been very substantially decreased. In control experiments, treatment of the native hormone with 8 M urea did not affect its physical, spectral or biological properties. Amino acid analysis of the derivatives was completely in accord with that expected.
发现在没有变性剂的情况下用过氧化氢处理人绒毛膜促乳腺素会将其六个甲硫氨酸残基中的五个氧化为亚砜；未被氧化的残基是甲硫氨酸-170。通过排阻色谱法、圆二色光谱和胰蛋白酶消化速率测定，该衍生物与天然激素相同，但生物活性大幅下降。在8M尿素存在的情况下，所有甲硫氨酸都可以用过氧化氢氧化或用碘乙酸烷基化。这些完全甲硫氨酸修饰的衍生物的物理性质发生了显著变化，生物活性再次大幅下降。在对照实验中，用8M尿素处理天然激素不会影响其物理、光谱或生物学性质。衍生物的氨基酸分析与预期完全一致。
