Ball Ronald O, Courtney-Martin Glenda, Pencharz Paul B
Department of Nutritional Science and Pediatrics, the University of Toronto, Toronto, Canada.
J Nutr. 2006 Jun;136(6 Suppl):1682S-1693S. doi: 10.1093/jn/136.6.1682S.
Sulfur amino acid metabolism has been receiving increased attention because of the link to chronic diseases such as cardiovascular disease, Alzheimer's disease, and diabetes. In addition, the role of cysteine and optimal intakes for physiological substrates such as glutathione are currently of considerable interest in human health. Although the dietary indispensability of methionine is not in question, the ability of cysteine to substitute for a portion of its requirement has been the topic of much debate. Methionine is often the most limiting amino acid in the diets of the developing world's population because of its low concentration in cereal grains. Therefore, the ability of cysteine to substitute for methionine requirement is not just biologically interesting; it is also of considerable economic and social importance. The primary goal of this review is to discuss the available evidence on the effect of cysteine substitution for methionine to meet the total sulfur amino acid requirement in adult humans, including an assessment of the methodological features of experiments with conflicting results. Assessment of the requirement experiments for amino acids with complex metabolism such as methionine and cysteine must begin with a careful definition of requirements and what substitution means. As a result of these definitions, a set of criteria for the intakes of methionine that will allow demonstration of the substitution effect have been developed. Some recent publications are assessed using these definitions and criteria, and a possible reason for the conflicting results in the literature is proposed. An approach to estimating tolerable upper intakes is also proposed. Research on in vivo sulfur amino acid metabolism in humans is tremendously difficult, and therefore, we do not wish to be overly critical of the high-quality work of the ambitious and highly intelligent men and women who have conducted various studies. Our goal is to objectively review the data for the reader in a logical and comprehensive manner and propose methods that may avoid difficulties in future studies.
由于与心血管疾病、阿尔茨海默病和糖尿病等慢性疾病存在关联，硫氨基酸代谢受到了越来越多的关注。此外，半胱氨酸的作用以及谷胱甘肽等生理底物的最佳摄入量目前在人类健康领域备受关注。尽管蛋氨酸在饮食中的不可或缺性毋庸置疑，但半胱氨酸替代其部分需求的能力一直是众多争论的焦点。在发展中世界人口的饮食中，蛋氨酸往往是最具限制性的氨基酸，因为其在谷物中的浓度较低。因此，半胱氨酸替代蛋氨酸需求的能力不仅在生物学上具有趣味性；它在经济和社会方面也具有相当重要的意义。本综述的主要目标是讨论关于半胱氨酸替代蛋氨酸以满足成年人总硫氨基酸需求的现有证据，包括对结果相互矛盾的实验的方法学特征进行评估。对蛋氨酸和半胱氨酸等代谢复杂的氨基酸的需求实验进行评估，必须首先仔细定义需求以及替代的含义。基于这些定义，已经制定了一套蛋氨酸摄入量标准，以证明替代效应。使用这些定义和标准对一些近期出版物进行了评估，并提出了文献中结果相互矛盾的一个可能原因。还提出了一种估计可耐受最高摄入量的方法。对人体硫氨基酸体内代谢的研究极其困难，因此，我们不想对进行了各种研究的雄心勃勃且高智商的男女所做的高质量工作过于挑剔。我们的目标是以合乎逻辑且全面的方式为读者客观地综述数据，并提出可能避免未来研究中出现困难的方法。
