Radiation inactivation of bovine intestinal alkaline phosphatase

Abstract The effects of 60 Co γ-radiation on aqueous solutions of alkaline phosphatase have been studied. The primary radicals of water radiolysis, e − aq , OH· and H· all contribute to the observed inactivation with inactivating efficiencies of 0.019, 0.019 and 0.04, respectively; O − 2 also causes inactivation (efficiency = 0.014). The radical anions (SCN) − 2 , (Br) − 2 and (I) − 2 cause inactivation at neutral pH and evidence is presented that cysteine and histidine residues are sites for radical anion reaction. Kinetic evidence suggests that inactivation is due to general denaturation of the protein, rather than destruction of the substrate binding site. Fractionation of the irradiated solution using FPLC following by analysis using fluorescence spectroscopy suggests that one process which leads to inactivation is the formation of alkaline phosphatase dimerized via tyrosine residues.