Non-Thermal Effect of Ceramics Radiation on Folate Structureand on Xanthine Oxidase Inhibition by Folate.

概要

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Folic acid was irradiated under cooling at 10°C in a slightly alkaline solution with a ceramics radiator (surface temperature: 68°C). The difference spectra of the folate against the non-irradiated one showed a red shift. The difference absorbance of the peak at the wavelength above 320 nm increased with the radiation time. Affinity of the irradiated folate (FA(+)), which is a competitive inhibitor, to the irradiated xanthine oxidase (XO(+)) more increased than the irradiated substrate with increasing temperature of the reaction, while the affinity to the non-irradiated enzyme (XO (-)) significantly decreased. The difference of the standard entropy change in the FA(+)/XO (-) system to that in the non-irradiated FA(-)/XO(-) system, i.e., Δ(ΔSS) gave a large negative value, while Δ(ΔSS) of the FA(-)/XO(+) system gave a large positive value. An increase in the Δ(ΔSS) of the FA(+)/XO(+) system over-came an increase in the enthalpy difference Δ(ΔHS) of the system, and then the free-energy difference Δ(ΔGS) resulted in the most negative value. This means that the driving force by the reaction system depends on an entropy effect. These results indicate that the red shift of the spectra of FA(+) is due to a solvent ordering effect obtained by the radiation, and that the affinity of the FA(+) to the active center of XO(+) increases when XO has also received the ordering effect.