ISOFORMS OF APOLIPOPROTEIN-A-I IN THE SERUM OF BROWN BULLHEADS (AMEIURUS-NEBULOSUS) WITH LIVER-CANCER

Brown bullheads (Ameiurus nebulosus) express two different isoforms of apolipoprotein A-I in the serum, a predominant form characterized by a pI of 6.9 and a more acidic isoform with a pI of 6.65. The two prote ins were identified by N-terminal amino acid sequencing, with 50 resid ues for the pI 6.9 isoform and 20 residues for the pI 6.65 isoform. Se quences for the two proteins were identical for the first 20 amino aci ds; however, differences in their primary sequences were deduced by an alysis of peptide maps obtained through proteolytic digestion. The rat io of the isoforms changes from 75% pI 6.9/25% pI 6.65 (no tumors) to equal amounts of both isoforms in bullheads with hepato- or cholangio- cellular carcinomas. This is the first report of these serum isoforms in feral fish showing that the expression of these proteins is directl y related to both cholangio- and hepato-cellular carcinomas. The poten tial use of these proteins as tumor biomarkers is discussed.