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.