amyloid

amyloid
1. Any of a group of chemically diverse proteins that appears microscopically homogeneous, but is composed of linear nonbranching aggregated fibrils arranged in sheets when seen under the electron microscope; it stains dark brown with iodine, produces a characteristic green birefringence in polarized light after staining with Congo red, is metachromatic with either methyl violet (pink-red) or crystal violet (purple-red), and fluoresces yellow after thioflavine T staining; a. occurs characteristically as pathologic extracellular deposits (amyloidosis), especially in association with reticuloendothelial tissue; the chemical nature of the proteinaceous fibrils is dependent upon the underlying disease process. 2. Resembling or containing starch. [amylo- + G. eidos, resemblance]

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am·y·loid 'am-ə-.lȯid n
1) a nonnitrogenous starchy food
2) a waxy translucent substance consisting primarily of protein that is deposited in some animal organs and tissue under abnormal conditions (as in Alzheimer's disease) see BETA-AMYLOID
amyloid adj

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n.
a glycoprotein, resembling starch, that is deposited in the internal organs in amyloidosis. b-amyloid protein has been found in the brains of Alzheimer's patients but the significance of this is unclear.

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am·y·loid (amґə-loid) [amylo- + -oid] 1. resembling starch; characterized by starchlike staining properties. 2. a substance produced by the action of sulfuric acid on cellulose, which gives a blue color when treated with iodine. 3. the pathologic extracellular proteinaceous substance deposited in amyloidosis; it is a waxy eosinophilic material that exhibits a green birefringence under polarized light when stained with Congo red. Amyloid deposits are composed primarily of straight, nonbranching fibrils 7.5–10 nm in diameter and of indefinite length, arranged either in bundles or in a feltlike meshwork; each fibril is composed of identical polypeptide chains arranged in stacked antiparallel β-pleated sheets. Although different forms have similar appearance, the protein in each is different.

Medical dictionary. 2011.

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