FIRST EVIDENCE FOR THE EXISTENCE OF MULTIPLE ISOFORMS OF BOVINE SERUMAMYLOID-A (APOSAA)

Bovine serum amyloid-A (SAA) was purified from acute-phase high densit y lipoprotein (HDL) by affinity chromatography and subsequent gel filt ration chromatography. The identity of the isolated protein was checke d by Western blotting following SDS-urea-PAGE using antisera raised ag ainst the purified protein fraction (SAA) and Amyloid A (AA). The anti serum raised against the purified SAA stained Congo red positive regio ns in the kidney of an AA-amyloidotic cow and reacted on Western blot with an AA-related protein of approximately 14 kDa. Moreover, it immun ostained two to three bands, of approximately 14 kDa, present in serum from diseased cows, proportionally to the serum SAA concentration as measured by ELISA. Isoelectric focusing of the purified bovine SAA fra ction revealed three major (pi 5.5, 6.0, 6.4) and three minor (pi 4.8, 5.0, 7.3) isoforms and two-dimensional SDS-urea-PAGE confirmed the id entity of the major isoforms. Isoelectric focusing of SAA isolated fro m sera, obtained from cows affected with different diseases, showed a variable ratio of the isoforms. In SAA isolated from serum obtained fr om a cow suffering from spontaneous AA-amyloidosis only one isoform (p I 4.8) was detectable. It is concluded that the results give first evi dence for the existence of multiple isoforms of bovine SAA, occurring in different plasma concentration ratios during different diseases.