Amyloid protein SAA is an apoprotein of mouse plasma high density lipoprotein

Mouse plasma contains a protein antigenically related to mouse protein AA, the principal protein derived from tissue deposits of amyloid substance in mice. In this work the plasma antigen, SAA, was found mainly as a high molecular weight form (2 x 10(5)) residing for the most part in the density interval 1.063-1.21 g/cm3 (high density lipoprotein, HDL); the largest amount of SAA, absolute and relative to total protein, was found in the density interval 1.125-12.1 g/cm3 (HDL3). When apoproteins of the mouse HDL obtained by delipidation of the lipoprotein particles were chromatographed in acid/urea, the antigenic activity appeared in the 10,000- to 15,000-dalton portion of the apoprotein complex. In these characteristics mouse SAA closely resembles human SAA and the behavior of the protein related to amyloid protein AA indicates that is one of the apoproteins of the HDL complex in both species. Therefore we suggest that it be named apoSAA.