Species-specific differences in glycogen phosphorylase among four tuna species

Four out of the five species of tuna commercially harvested in the United States are members of the genus Thunnus. These four species, albacore tuna (T. alalunga), bigeye tuna (T. obesus), bluefin tuna (T. thynnus), and yellowfin tuna (T. albacares) are genetically very similar and, therefore, can be difficult to distinguish from one another. Both the yellowfin tuna embargo policy and the Atlantic bluefin tuna regulations have precipitated an urgent need for a reliable test procedure for distinguishing among these species in order to detect mislabeling and economic fraud. Protein fractions exhibiting glycogen phosphorylase activity were isolated from these four tuna species using anion-exchange perfusion chromatography. Species-specific differences in these protein fractions were demonstrated using nonlinear narrow pH range isoelectric focusing in rehydratable thin layer polyacrylamide gels. The potential for using these protein fractions as immunizing antigens for the production of species-specific monoclonal antibodies is discussed.