Question

Do the electrostatic potential maps and the calculated electrostatic coefficients on the C atoms predict the same pattern of shielding/deshielding for the aromatic protons in phenacetin? Which is easier to interpret (explain this answer)?

Answer 1

Fig

Xiv

No, they not predict the same pattern of shielding.

Calculated electrostatic coefficients on the C is easier to interpret bacause Intraproteic electrostatic potentials along the catalytic triad in serine proteinases are compared for eight enzymes for which three-dimensional co-ordinates are available. We used our bond-increment method to calculate the potential and we considered all protein atoms, including hydrogens. It was found that counter ions which may be located in the vicinity of charged surface side chains play a decisive role in determining enzymatic action. If ionizable side chains are neutralized the electrostatic potential curve across the catalytic triad is of minimum character in all investigated enzymes. It stabilizes the (- + -) charge distribution which models the Ser−-His+-Asp− transition state structure which is formed during the catalytic process. Based on the close similarity of the electrostatic pattern in various enzymes we call attention to the possibility that convergent evolution produced not only the effective catalytic triad but also a minimum-type potential which accelerates the enzymatic reaction.

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