The contributions of secondary proton bridges to the catalytic power of the serine proteases

The curvature of proton‐inventory functions (rate constants in mixtures of protium and deuterium oxides) for hydrolysis of substrates of varying structure by trypsins from four different sources has been used as a signal of transition‐state stabilization by a short, strong hydrogen bonds (“low‐barrier hydrogen bonds”) at the histidine‐aspartate site of the catalytic triad. Previous estimates suggested contributions as large as 85 kJ mol −1 but the current findings are consistent with contributions of no more than a few kJ mol −1 .