Studies on the Interaction between Regulatory Enzymes and Effectors

The effect of 38 structural analogues of AMP on glycogen phosphorylase b has been studied in order to determine which functional groups or atoms of AMP are important for the binding to and activation of the enzyme. Among the compounds tested, 21 were activators, and the mode of interaction was analyzed kinetically in terms of the maximal activation and the activation constant which was the concentration giving a half-maximal activation. With 12 compounds, which did not activate the enzyme but counteracted the activation by AMP, the inhibition constant against the activation was determined for the evaluation of the binding capacity. The results indicated the following: The amino group at position 6 and the nitrogen atom at position 1 were effective in the binding; the hydroxyl group at position 2 of the ribose moiety contributed both to the binding and to the activation, while the hydroxyl group at position 3 did not; the monophosphate group was absolutely required and should be located at position 5 of the ribose moiety for the activation.