RADIATION INACTIVATION OF BOVINE INTESTINAL ALKALINE-PHOSPHATASE

The effects of Co-60 gamma-radiation on aqueous solutions of alkaline phosphatase have been studied, The primary radicals of water radiolysi s, e(aq)-, OH. and H. all contribute to the observed inactivation with inactivating efficiencies of 0.019, 0.019 and 0.04, respectively; O2- also causes inactivation (efficiency = 0.014). The radical anions (SC N)2-, (Br)2- and (I)2- cause inactivation at neutral pH and evidence i s 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 s ubstrate binding site. Fractionation of the irradiated solution using FPLC following by analysis using fluorescence spectroscopy suggests th at one process which leads to inactivation is the formation of alkalin e phosphatase dimerized via tyrosine residues.