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An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized ''de novo (from scratch)'' by the organism, but must be supplied in its diet. The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine (i.e., F V T W M L I K H).〔Dietary Reference Intakes: The Essential Guide to Nutrient Requirements, published by the Institute of Medicine's Food and Nutrition Board, currently available online at http://fnic.nal.usda.gov/dietary-guidance/dietary-reference-intakes/dri-reports〕 Six other amino acids are considered conditionally essential in the human diet, meaning their synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress.〔 These six are arginine, cysteine, glycine, glutamine, proline and tyrosine (i.e. R C G Q P Y). Five amino acids are dispensable in humans, meaning they can be synthesized in the body. These five are alanine, aspartic acid, asparagine, glutamic acid and serine (i.e., A D N E S).〔 ==Essentiality in humans== ( *) Essential only in certain cases. ( * *) Pyrrolysine, sometimes considered "the 22nd amino acid", is not listed here as it is not used by humans.〔(【引用サイトリンク】title=Newsletter 2009, Biochemical Nomenclature Committee of IUPAC and NC-IUBMB )〕 Eukaryotes can synthesize some of the amino acids from other substrates. Consequently, only a subset of the amino acids used in protein synthesis are essential nutrients. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Essential amino acid」の詳細全文を読む スポンサード リンク
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