INTERACTION OF GLUCAGON WITH DIMYRISTOYLPHOSPHATIDYLCHOLINE IN VESICULAR AND DISCOIDAL COMPLEXES

Glucagon fragments dimyristoylphosphatidylcholine liposomes into disco idal complex under appropriate conditions, The concentration of glucag on required to fragment the vesicles increases with increasing pH, whi ch appears to be related to the glucagon binding, It was also observed that the fragmentation is facilitated by NaCl, which is also due to i ncreased glucagon binding, From the quenching of Trp fluorescence by d oxyl group located at various positions of the acyl chain of the lipid , Trp of glucagon was found to be located close to the bilayer surface in the vesicular complex, However, the Trp fluorescence was quenched by the doxyl group in the discoidal complex to an equal extent regardl ess of the position of this spin label in the acyl chain, This and the results of second derivative UV spectroscopy of Tyr suggested that se gments including Tyr-13 and Trp-25 are involved in the discoidal compl ex formation and that the orientation of glucagon is not normal to the bilayer surface.