Major acute phase protein. Homohexamer; dimer of trimers. Can form amyloid fibrils after partial proteolysis; the native, undenatured protein does not form amyloid fibrils (in vitro). Apolipoprotein of the HDL complex. Binds to heparin (By similarity). Detected in liver. By bacterial lipopolysaccharide. Reactive, secondary amyloidosis is characterized by the extracellular accumulation in various tissues of the SAA protein. These deposits are highly insoluble and resistant to proteolysis; they disrupt tissue structure and compromise function. SAA2 is more amyloidogenic than SAA1. Belongs to the SAA family.