Identification of hepatic Z-protein in a marine elasmobranch, Platyrhinoides triseriata

Previous studies were unable to identify Z-protein in elasmobranch liver with bromosulphophthalein as ligand. By using 8-anilinonaphthalene-1-sulphonate and Rose Bengal as ligands, however, we demonstrated in hepatic cytosol from Platyrhinoides triseriata an organic-anion-binding protein with gel-filtration characteristics identical with those of rat Z-protein. By comparison with pooled rat Z-protein, Pl. triseriata Z-protein had slightly lower affinity for 8-anilinonaphthalene-1-sulphonate and Rose Bengal, greatly decreased binding affinity for bromosulphophthalein and no binding activity for oleic acid or squalene. The Pl. triseriata Z-protein binding site was less hydrophobic than that of rat Z-protein. This observation may explain the differences in binding characteristics between the Z-proteins of these species.