amyloid

Pronunciation: am′i-loyd

Definition:

1. Any of a group of chemically diverse proteins that appear microscopically homogeneous but are composed of linear nonbranching aggregated fibrils arranged in sheets when seen under the electron microscope; amyloid 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.
2. The pathologic extracellular proteinaceous substance deposited in amyloidosis. There are two major types of amyloid protein: amyloid light chain protein that occurs in primary amyloidosis and amyloid, a protein that occurs in reactive systemic amyloidosis.
3. Resembling or containing starch.

[amylo- + G. eidos, resemblance]

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