The Burden Borne by Enzyme Catalysts

By contrast, kcat/f m for enzymatic catalysis of deprotonation at carbon is not strongly dependent on intrinsic carbon acidity. For example, kcat/ m is close to the diffusion-controlled limit for both the ketosteroid-isomerase-catalyzed deprotonation of the ketone 1 (pK 13) [39] and the triosephosphate-isomerase-catalyzed deprotonation of the ketone 3 (pK 18) [40]. An extreme example is the small difference in the values of kcat/Km = 3 x 10 and 1.4 x 10 s for enzyme- 

Efficient catalysis of deprotonation of strongly acidic carbon that undergoes rela- 

Substituent Effects on Equilibrium Constants for Deprotonation of Carbon 

Substituent Effects on Rate Constants for Proton Transfer at Carbon 

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