Ellinger G M
Ann Nutr Aliment. 1978;32(2-3):281-9.
The background to earlier experiments that were designed to evaluate the nutritional availability of peptide-bound methionine sulphoxide is described. After mild acid hydrogen peroxide treatment of casein, NPU had fallen from 71 to 58. A gas-chromatographic analysis for intact methionine residues that has been developed since then has shown that in the oxidised casein all methionine residues had been oxidised to the sulphoxide, whereas in several foods only moderate levels of sulphoxide were found. The methionine potency of sulphoxide residues is considered to be less a function of digestion and absorption than of the body's capacity to reduce it to methionine. Evidence is given that hydrogen peroxide also modified cystine residues in casein to be rendered nutritionally unavailable. On a molar basis, half the sulphur amino acids in most foods is furnished by cystine which therefore plays a more important role in protein nutrition than is generally recognised.
本文描述了早期旨在评估肽结合蛋氨酸亚砜营养可利用性的实验背景。用温和的酸性过氧化氢处理酪蛋白后，蛋白质净利用率（NPU）从71降至58。从那时起开发的一种用于完整蛋氨酸残基的气相色谱分析表明，在氧化的酪蛋白中，所有蛋氨酸残基都已氧化为亚砜，而在几种食物中仅发现了中等水平的亚砜。亚砜残基的蛋氨酸效价被认为与其说是消化和吸收的函数，不如说是身体将其还原为蛋氨酸的能力的函数。有证据表明，过氧化氢还会修饰酪蛋白中的胱氨酸残基，使其在营养上无法利用。按摩尔计算，大多数食物中一半的含硫氨基酸由胱氨酸提供，因此胱氨酸在蛋白质营养中发挥的作用比一般认为的更为重要。
