SAA, an apoprotein of HDL: its structure and function.

The putative precursor of amyloid protein AA appears in serum as an apoprotein (apoSAA) of heavier HDL fractions of lipoproteins found in humans and mice. ApoSAA is found by precipitation with specific anti-AA antibodies to be on a particle that also carries apoA-I and some C-apoproteins. In endotoxin-treated mice a lipoprotein fraction with about 2 moles of apoSAA to 1 mole of apoA-I can be isolated, an apoSAA-carrying subset of HDL being thus suggested. In mice, rapid clearance from plasma of native apoSAA compared to apoA-I suggests a special function for apoSAA. The C-terminal amino acid portion of apoSAA may play a role in this function.