The role of metal ions in the radiosensitivity of metalloproteins

The radiation-induced inactivation of dilute solutions of three forms of bovine carbonic anhydrase (metal-free apo-BCA, Zn2+-BCA and Co2+-BCA) has been studied. The presence of the metal ions did not alter the sensitivity of the enzyme to inactivation of oxidizing radicals; however, they exerted a protective effect against inactivation by reducing radicals. Data obtained using the amino-acid-specific inorganic radical anions (CNS)2- and Br2- allowed the identification of histidine, tyrosine and tryptophan as residues essential to the activity of bovine carbonic anhydrase when assayed by p-nitro-phenylacetate. (author)