Ribonuclease proton inventory

Anslyn E, Breslow R. Proton inventory of a bifunctional ribonuclease model. J. Am. Chem. Soc. 1989 111 8931-8932. 

The pH vs rate profile showed a bell-shaped curve indicating that this catalyst uses both B and BH+ in a bifunctional mechanism. As with the enzyme, the bis-imidazole catalyst can perform its bifunctional catalysis by a simultaneous mechanism, not the sequential mechanism of simple buffer catalysis. We saw that this was indeed the case, as revealed by the tool called "proton inventory." In this technique the reaction is performed in D2O, in H2O, and in mixtures of the two. If only one proton that can exchange with D2O is moving in the transition state, the points all lie on a straight line between the H2O and slower D2O points. If two (or more) protons are moving, the line is curved. It had been found for the enzyme ribonuclease A [10] that a curved line was seen corresponding to the movement of two protons, and we also saw a curved plot—with very similar data— for our cyclodextrin-6A,6B-bisimidazole catalyst 6 [11]. Controls established that indeed this was a reliable indication that our system is performing simultaneous bifunctional catalysis, just as the enzyme does. In particular, the... 

The Use of a Proton Inventory to Explore the Mechanism of Ribonuclease Catalysis... 

The Use of a Proton inventory to Explore the Mechanism of Ribonuclease Catalysis 440 A Substituent Effect Study to Decipher the Reason for the High Stability of Collagen 444 Using a Hammett Plot to Explore the Behavior of a Catalytic Antibody 450... 

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