The enzymatic mechanism is similar to that of other serine proteases. These enzymes contain a catalytic triad consisting of histidine-57, aspartate-102, and serine-195.[7] This catalytic triad was formerly called a charge relay system, implying the abstraction of protons from serine to histidine and from histidine to aspartate, but owing to evidence provided by NMR that the resultant alkoxide form of serine would have a much stronger pull on the proton than does the imidazole ring of histidine, current thinking holds instead that serine and histidine each have effectively equal share of the proton, forming short low-barrier hydrogen bonds therewith.[8][page needed] By these means, the nucleophilicity of the active site serine is increased, facilitating its attack on the amide carbon during proteolysis.