A Radiation Chemical Study of the Inactivation and Active Site Composition of Carboxypeptidase A

Abstract

Steady-state and pulsed irradiation techniques have been applied to the inactivation of carboxypeptidase A. The solvated electron was found to be ineffective as an inactivating species, although it rapidly localized on a disulphide bond. Inactivation of the enzyme with low efficiency was observed for OH and O₂⁻ radicals, but H atoms are more efficient. Some secondary radicals derived from OH were also found to lead to inactivation. A correlation between the sensitivity of the enzyme to inactivation by the secondary radicals, and the reactivity of these radicals with the enzyme and with free amino acids, led to the identification of tyrosine and tryptophan residues present in the active site of the enzyme.