Amyloid

It is a water-soluble starch-like polysaccharide (etymology: amylose + eidos (resemblance)) that is found in the cell walls of cotyledons in many seeds and turns blue when reacted with iodine. It is a polymer of proteinaceous fibers that show hyperrefractive properties under polarized light when stained with Congo red. For example, the polysaccharide of tamarind seed mucilage has a structure in which one α- D -xylopyranose group and 2- O -β- D -galactopyranosyl-α- D -xylopyranose group are linked at the _C6 position to a linear chain of (1 → 4) linked β- D -glucopyranose. Its X-ray diagram resembles that of cellulose II regenerated cellulose. When cellulose is treated with sulfuric acid, it is partially hydrolyzed into a type of amyloid, so the surface of parchment paper contains a lot of amyloid. In the biological and medical fields, it is a general term for deposits found in living organisms, mainly composed of proteins, and is often fibrous. The one related to Alzheimer's disease is called amyloid β protein (Aβ). Aβ is a fragment produced when the extracellular domain is cleaved from a membrane-spanning precursor, and is prone to aggregation, which exerts strong cytotoxicity.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

多くの種子中の子葉細胞壁に含まれ，ヨウ素反応で青色を呈するデンプン類似の水溶性多糖(語源：amylose＋eidos(resemblance))で，コンゴーレッド染色で，偏光下に重屈折性を示すタンパク質性の繊維の重合体をさす．たとえば，タマリンド種子粘質物の多糖は(1→4)結合したβ-D-グルコピラノースの直鎖に C₆ 位で1個のα-D-キシロピラノース基と2-O-β-D-ガラクトピラノシル-α-D-キシロピラノース基が結合した構造を有する．そのX線図はセルロースⅡ再生セルロースに類似する．セルロースを硫酸処理すると，一種のアミロイドに部分加水分解されるため，硫酸紙の表面はアミロイドを多く含む．生物・医学分野では，生体に見られる沈着物質の総称で，タンパク質を主成分とし，繊維状のものが多い．アルツハイマー病に関連したものは，アミロイドβタンパク質(Aβ)とよばれる．Aβは，細胞膜貫通型の前駆体から細胞外領域が切り出されて生じるフラグメントで，凝集しやすく，凝集体は強い細胞毒性を発揮する．

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