Direct Measurement of Local and Global Contributions in the Binding of Coformycin to Bovine Adenosine Deaminase

Abstract

A general method is outlined that determines quantitatively the extent to which tight ligand binding to an enzyme active site is facilitated by the adoption of a stabler macromolecular conformation in the complex. The method therefore rejects the general assumption that competitive inhibitor binding to enzyme active sites involves only local (active site) interactions. The procedure involves comparing the unfolding transition state free energies of the free and complexed enzyme from physiological conditions. For the interaction of the transition state analog coformycin with bovine adenosine deaminase we observed that the binding free energy by the physiological enzyme was ~92% due to the assumption of a stabler enzyme conformation in the complex. The significance of these findings in terms of general enzyme catalysis is discussed.

Keywords::

• Enzyme Catalysis
• Shifting Specificity Model
• Adenosine Deaminase
• Coformycin
• Transition State Analog
• Binding