THE ACUTE-PHASE SERUM AMYLOID A PROTEIN (SAA) IN THE HORSE - ISOLATION AND CHARACTERIZATION OF 3 ISOFORMS

Serum amyloid A (SAA) from acute phase horse serum was isolated using hydrophobic interaction chromatography, gel filtration and ion exchang e chromatography. Three SAA isoforms with different isoelectric points , i.e. SAA pi 8.0, SAA pi 9.0 and SAA pi 9.7, were identified by two-d imensional electrophoresis and further characterized with amino acid s equence analysis. These isoforms were found in similar concentrations in all animals investigated, with SAA pi 9.7 constituting about half o f the total SAA content. Partial amino acid sequence analysis verified the previously published heterogeneous SAA sequence. SAA pi 8.0 was f ound to have isoleucine in Position 16, glutamine in Position 44 and g lycine in Position 59. SAA pi 9.0 had leucine, glutamine and alanine i n the corresponding positions. In SAA pi 9.7 leucine, lysine and alani ne were detected. The three isoforms characterized in this study are a ll acute phase SAAs. SAA pi 9.0 and 9.7 correspond to amyloid A protei n variants previously isolated from amyloid deposits of equine liver, while there are no reports on an amyloid A variant corresponding to SA A pi 8.0. (C) 1997 Elsevier Science B.V.