| precursor | Something that precedes. 1. <biochemistry> In biological processes, a substance from which another, usually more active or mature substance is formed. 2. In clinical medicine, a sign or symptom that heralds another. Origin: L. Praecursor = a forerunner (18 Nov 1997) |
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| precursory cartilage | A cartilage that is normally replaced by bone, to form a part of the skeleton. Synonym: ossifying cartilage, precursory cartilage. (05 Mar 2000) |
| Amine Precursor Uptake and Decarboxylation | <pharmacology, physiology> Paracrine cells of which argentaffin cells are an example. Usage of the term APUD is neither helpful nor memorable. Acronym: APUD (11 Nov 1997) |
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| amyloid beta-protein precursor | A precursor to the amyloid-beta protein (beta/a4). Alterations in the expression of the amyloid beta-protein precursor (abpp) gene, located on chromosome 21, plays a role in the development of the neuropathology common to both alzheimer disease and down syndrome. Abpp is associated with the extensive extracellular matrix secreted by neuronal cells. Upon cleavage, this precursor produces three proteins of varying amino acid lengths: 695, 751, and 770. The beta/a4 (695 amino acids) or beta-amyloid protein is the principal component of the extracellular amyloid in senile plaques found in alzheimer disease, down syndrome and, to a limited extent, in normal aging. (12 Dec 1998) |
| amyloid precursor protein | <protein> Individuals with Alzheimer's disease are characterised by extensive accumulation of amyloid in the brain, referred to as senile plaques. These consist of a core of amyloid fibrils surrounded by dystrophic neurites. The principal component of the amyloid fibrils is B/A4, a peptide derived from the larger APP. The specific role of amyloid protein is unclear but it is thought that amyloid deposits may cause neurons to degenerate. Amyloid deposits also occur in brains of older Down's Syndrome patients. (04 May 1997) |
| angiotensin precursor | angiotensin |
| enzyme precursor | <biochemistry> Inactive precursors that can be converted to active enzymes. Enzyme precursors containing extra-long polypeptide chains that block activity are activated by acid or enzymatic hydrolysis to remove the inhibiting portion. (12 Dec 1998) |