STRUCTURAL-CHANGES AROUND THE ALKALINE PKA OF CARBOXYPEPTIDASE-A

X-ray Absorption Fine Structure (XAFS) experiments have been performed to probe detailed structural changes at the active site of carboxypep tidase A (ZnCPD) from neutral to alkaline pHs. Direct comparison and a nalysis on the first coordination shells of ZnCPD revealed structural differences between pH 7.0 and pH 9.9. The observed structural changes indicated that one of the ligands to the metal moves to a 0.09 angstr om shorter distance from the zinc ion at the alkaline pH, resulting in a shorter metal-ligand distance and an increased first shell structur al disorder. Such a situation would be expected if the water ligand of the zinc ion was converted to hydroxide at the alkaline pH.