期刊名称：Journal of Nutritional Science and Vitaminology
印刷版ISSN：0301-4800
电子版ISSN：1881-7742
出版年度：1993
卷号：39
期号：5
页码：425-435
DOI：10.3177/jnsv.39.425
出版社：Center for Academic Publications Japan
摘要：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 ( Δ SS) gave a large negative value, while Δ ( Δ SS) of the FA(-)/XO(+) system gave a large positive value. An increase in the Δ ( Δ SS) of the FA(+)/XO(+) system over-came an increase in the enthalpy difference Δ ( Δ HS) of the system, and then the free-energy difference Δ ( Δ GS) 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.
