The different protein sources (Cricetulus griseus or Homo sapiens) should not cause a significant impact on our results, since the ITC results for the human PKA are very comparable to already published PKA arising from Cricetulus griseus. The ATP pocket is conserved (primary sequence and protein structure as well) in both species and should not impact the crystallisation of the benzoic acid fragment: the six different amino acids are more than 6 Å away from the ATP pocket. The buffer medium used for protein crystallisation contains a considerable amount (see Table ) of apolar solvents such as dimethyldioxide (DMSO), methanol (MeOH) and 2-Methyl-2,4-pentanediol (MPD). In this enviroment, it is quite likely that the benzoic acid appears in the protonated (uncharged) form. Of course, this protonated form is in equilibrium with the deprotonated form which would be favored in the polar solvent water. However, already a small portion of the protonated form should be sufficient to successfully soak in the PKA protein crystal and bind in the ATP site in the protonated form.