THE CONTRIBUTIONS OF SECONDARY PROTON BRIDGES TO THE CATALYTIC POWER OF THE SERINE PROTEASES

The curvature of proton-inventory functions (rate constants in mixture s of protium and deuterium oxides) for hydrolysis of substrates of var ying structure by trypsins from four different sources has been used a s a signal of transition-state stabilization by a short, strong hydrog en bonds (''low-barrier hydrogen bonds'') at the histidine-aspartate s ite of the catalytic triad. Previous estimates suggested contributions as large as 85 kJ mol(-1) but the current findings are consistent wit h contributions of no more than a few kJ mol(-1).