Glycogen phosphorylase (EC 2.4.1.1.) is a regulatory enzyme whose activity is modulated by a complex mechanism which includes activation by AMP and inhibition by glucose 6-phosphate. The enzyme exists in two forms: phosphorylase b, a dimer inactive in the absence of AMP, and phosphorylase a, a tetramer which exhibits 80-90% of its maximum activity in the absence of the nucleotide. An understanding of the interaction of AMP or other effectors with the amino acid residues forming the respective binding sites may shed light on the mechanism of control at a molecular level. The objectives of the project are to prepare and characterize nondissociable activator-, inhibitor-, or substrate-enzyme complexes by using photoactivatable analogs of the natural substrate and effectors. The results of the initial studies indicated that 8-azidoadenosine 5'-monophosphate (N3AMP) competes with AMP for the allosteric site on phosphorylase. In the presence of U.V. light, N3AMP is irreversibly bound to phosphorylase; incorporation can be prevented by AMP. The aim of current research efforts is to increase the covalent binding of N3AMP or derivatives of N3AMP to the allosteric site on phosphorylase. BIBLIOGRAPHIC REFERENCES: Kuo, J.F., Kuo, W.N., Shoji, M., Davis, C.W., Seery, V.L. and Donnelly T.E. Purification and general properties of guanosine 3':5'-monophosphate-dependent protein kinase from guinea pig fetal lung. (1976) J. Biol. Chem. 251, 1759-1766. Seery, V.L. and Haley, B.E. Activation of glycogen phosphorylase by 8-azidoadenosine 5'-monophosphate. (1976) Fed. Proc. 35, 1669 (ABS #1600).