THE PRIMARY STRUCTURE OF SERUM AMYLOID-A PROTEIN IN THE SHEEP - COMPARISON WITH SERUM AMYLOID-A IN OTHER SPECIES

Serum amyloid A (SAA) protein was isolated from acute phase sheep sera by ultracentrifugation, gel filtration and ion-exchange chromatograph y. The purified protein was characterized by sodium dodecylsulfate pol yacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing, amin o acid composition and Edman degradation. Protein SAA sheep consists o f 112 amino acid residues and has a blocked N-terminus. The amino acid sequence showed a high degree of homology with SAA proteins from othe r species, especially at positions 32 to 54, indicating that this part icular part of the protein is important for its function. When compare d to human protein SAA, nine inserted amino acids could be demonstrate d, located in regions 69 to 77. Similar observations have been seen in cow, horse, dog, cat, and mink protein SAA. Heterogeneities were foun d in positions 28, 55, 63, 64, 66, 75, 77, 78, 80 and 89. Positions 63 , 64, 66, 75, 77, 78 and 80 revealed the existence of a minor gene pro duct of protein SAA sheep. The minor variant of protein SAA sheep is i dentical in these positions with the corresponding positions in protei n SAA cow. By comparing the amino acid sequences of the different SAA proteins, two separate branches in the evolutionary pattern of protein SAA appear. One of the branches includes the species with the inserti on which represents also one of the more heterogeneous part of the pro tein.