The differences in the way the nucleophilic serine is deprotonated inβ-lactamases and serine proteases.

The potential differences are annotated on the edges, the direction of the edge indicating the direction of the potential difference. Ser70 cannot donate proton to Lys73 because of reverse potential gradient in β -lactamase. In serine proteases, the Ser195 however has the correct potential to donate the proton to His57.