COMPARABLE STRUCTURAL STABILITIES OF PENTA-COORDINATE AND HEXA-COORDINATE ZN(II) IN A SIMPLE-MODEL SYSTEM OF THE ACTIVE-SITE OF CARBOXYPEPTIDASE-A

Abstract

Ab initio studies of simple model systems for the carboxypeptidase A active site indicate that penta- and hexa-coordinate Zn(II) complexes have comparable structural stabilities. These facile coordination structures can be responsible for the catalytic role. Although the hexa-coordinate Zn(II) complex is more stable in enthalpy than the penta-coordinate Zn(II) complex, the entropy effect makes the latter as stable as or slightly more stable in free energy than the former.