抄録
Non-thermal effect of ceramics radiation on xanthine oxidase activity and the inhibitory effect of the irradiated inhibitors have been investigated using the enzyme, substrate, and competitive inhibitors which were separately irradiated under cooling. K_m values in the irradiated enzyme systems of both uric acid formation and superoxide production were reduced to 57〜50% of the non-irradiated control. Their V_<max>/K_m values were increased up to 163〜170% of the non-irradiated control. The K_i values for competitive inhibitors, i. e., folic acid, 5-formyltetrahydrofolate and allopurinol, in the irradiated enzyme system of superoxide production were 23, 41 and 100% of the non-irradiated control, respectively. Although these kinetic values were variously affected by the combination of the irradiated and non-irradiated components, the enzyme reaction was greatly affected when all components of the reaction were irradiated. Spectra of the 3h-irradiated folate showed a red shift of 50 to 60 kJ/mol. This suggests the existence of the intramolecular hydrogen bonding between pterin and 4-oxo residue which might be modified by a solvent ordering effect of the ceramics radiation. A steady-state thermodynamic molecular kinetic analysis for the reaction estimated the followings : (1) the irradiated enzyme may be kept in a folding state by such an entropy effect as a decrease or negative mode, (2) the formation of Michaelis complex has been accelerated, (3) the activated complex has been stabilized, (4) a solvation or an electro-striction with water of xanthine, folates and the active center of the enzyme may be promoted by irradiating the components in aqueous solution. These results suggest that the ceramics radiation has caused the regulation of the enzyme activity and the modification of the folate structure in aqueous solution through the solvent ordering effect.
