An extreme case with a very low PCVA rank (178) compared to CSA (10) and FSA (10-11) is SER71. This residue is located very close to the active site and thus potentially important for ligand binding, but it shows a very low electrostatic effect on the substrates and is thus not detected by PCVA. Another case is SER118, which is ranked about 30 places lower in PCVA than in CSA and FSA. Both these cases concern serine residues, which might show only a small electrostatic effect.