Institution: | a Food Technology Division, Flesh Food Biochemistry Section, BARC, Mumbai 400 085, India b Radiation Chemistry & Chemical Dynamics Division, BARC, Mumbai 400 085, India c Department of Biochemistry, Seth G. S. Medical College, KEM Hospital, Mumbai 400 012, India |
Abstract: | Ionizing radiation inactivated purified chicken intestinal aminopeptidase in media saturated with gases in the order N2O>N2>air. The D37 values in the above conditions were 281, 210 and 198 Gy, respectively. OH radical scavengers such as t-butanol and isopropanol effectively nullified the radiation-induced damage in N2O. The radicals (SCN)2??, Br2?? and I2?? inactivated the enzyme, pointing to the involvement of aromatic amino acids and cysteine in its catalytic activity. The enzyme exhibited fluorescence emission at 340 nm which is characteristic of tryptophan. The radiation-induced loss of activity was accompanied by a decrease in the fluorescence of the enzyme suggesting a predominant influence on tryptophan residues. The enzyme inhibition was associated with a marked increase in the Km and a decrease in the Vmax and kcat values, suggesting an irreversible alteration in the catalytic site. The above observations were confirmed by pulse radiolysis studies. |