Other forms of amyloid exist. In chronic long-term hemodialysis, patients often develop a carpal tunnel syndrome, arthritis and cystic bone lesions, all due to amyloid. The protein isolated has been [32 microglobulin, a single chain low molecular weight (11.8 kDa) polypeptide that is continually shed from all membranes. It does not pass through most dialysis membranes and in chronic hemodialysis its concentration may rise 50-fold. The specific local factors influencing its precipitation as amyloid are not yet known.
It has long been known that the senile plaques of Alzheimer disease stain positively for amyloid. The amyloid fibrils of the senile plaque and cerebral amyloid angiopathy from both Alzheimer disease and Down syndrome have been isolated and identified as
3 protein (also known as A4 protein), a 4.2 kDa protein (39 amino acid segment isolated from vessels; 43 amino acid segment from plaques). The 28 N-terminal amino acids are almost identical in the senile plaques and vessel. Beta protein is derived from a 695 amino acid glycoprotein of 79 kDa (3 amyloid protein precursor AfJPP) that crosses and constitutes part of the cell membrane. The precise cause of the cleavage of the A(3PP is not known, but aberrant degradation involving serine protease inhibitors such as al antichymotrypsin (ACT) which is regularly found in plaques has been suggested.
See also: Acute phase proteins; Bence Jones proteins; (^-microglobulin; Lymphoma.
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