ARE THERE LIMITS TO ENZYME-INHIBITOR BINDING-DISCRIMINATION - INFERENCES FROM THE BEHAVIOR OF NUCLEOSIDE DEAMINASES

An enzyme can enhance the rate of a reaction only to the extent that i t binds the altered substrate in the transition state (S-not equal) mo re tightly than it binds the substrate in the ground state. Inhibitors that resemble S-not equal can be used to stop an enzyme from working, probe its mechanism of action and obtain exact structural information about intermediates in catalysis. In S-not equal analog inhibitors of adenosine and cytidine deaminases, a single hydroxyl group appears to make extremely large contributions to binding affinity. The magnitude of this contribution becomes even more striking when differences in f ree energy of solvation by water are taken into account. Other results , obtained by deleting individual binding determinants, indicate the o peration of remarkable levels of cooperativity and suggest that if eve ry group is in exactly the right position and is part of an inflexible structure, then a single substituent or H-bond can produce very large increases in binding affinity. Some implications for inhibitor design are considered.