ISOLATION AND CHARACTERIZATION OF MUSCOVY (CAIRNA-MOSCHATA) DUCK INSULIN

Ducks (Anatidae Family, Anseriform order) are divided in two genera: P ekin duck (Anas platyrhynchos genus) and Muscovy duck (Cairina moschat a genus) and differ for their number of liver insulin receptors (despi te rather similar plasma insulin levels). The possibility that the pre sence of different endogenous insulins account for the difference in i nsulin receptor number between the two duck species led us to purify, sequence and characterize the binding properties of Muscovy duck insul in. The sequence of Muscovy duck insulin (measured mass: 5729.11) was indentical to that described in two other species from the Anseriforme order: Pekin duck or goose. The binding affinity of Muscovy duck insu lin for rat liver insulin receptors (either membrane bound or solubili zed receptors) was lower than that of porcine insulin (0.3), which mos t likely accounts for the low biological potency of Pekin duck insulin previously described. In contrast, liver receptors from chicken and b oth duck species exhibited the same affinity for duck and porcine insu lin suggesting the presence of specific changes in the structure of bi nding sites of bird liver insulin receptors. The decrease in the numbe r of insulin receptors in Muscovy duck liver is not therefore the cons equence of a change at the level of the insulin molecule itself. As di scussed, among bird insulins, the hypoactive ''duck type'' insulin wou ld have appeared after the hyperactive ''chicken type'' insulin during the evolution of Aves.