amyloid precursor protein n a transmembrane protein from which beta-amyloid is derived by proteolytic cleavage by secretases abbr. APP
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(APP) a large transmembrane glycoprotein expressed on the cell surface, of uncertain function; it may be cleaved on the cell surface to a soluble form. Alternatively, cleavage may follow endocytosis, and in some cases then yields abnormal 40 to 43 amino acid peptides that aggregate to form Aβ amyloid associated with Alzheimer disease (q.v.).Medical dictionary. 2011.