Serum amyloid A, SAA.

Serum amyloid A (SAA) is the precursor protein of reactive amyloid fibrils in that a subunit protein of amyloid fibrils in reactive amyloidosis is a degradation product of SAA. There are multiple forms of SAA, each the product of a separate gene. All of the SAA proteins are apolipoproteins.

The SAA precursor of reactive amyloid fibril protein is an acute phase reactant, synthesized in response to almost all inflammatory disease. Under acute phase conditions, the plasma level of SAA may rise to 500–1000micrograms/ml, returning to a normal level of 1–2micrograms/ml. Multiple forms of SAA have been identified, and SAA1 and SAA2 are among the most sensitive indicators of acute phase reaction. SAA1 and SSA2 are single polypeptide chains with 104 amino acid residues. In reactive amyloidosis, SAA undergoes enzymatic degradation and the product is incorporated into amyloid fibrils. Reactive amyloidosis A is usually found in chronic...