Ion-exchange resins modified with some manganese(III)-porphyrins (Mn3+-Pr) show a uricase-like catalytic activity, which is applicable to the determination of uric acid. The resonance Raman spectra of Mn3+-Pr indicate that Mn3+-porphyrins on modified resins are reduced to Mn2+-porphyrins with oxidizing uric acid; Mn2+-porphyrins then return to Mn3+-porphyrins by oxidation with O2 in the reaction system. It was concluded on the basis of these results that the modified resins show an uricase-like activity by repeating this redox cycle of manganese-porphyrins on the modified resins. Mn3+-Pr exhibited no oxidative catalytic activity for 7-methylated derivatives of uric acid, indicating that the nitrogen atom at the 7-position of uric acid plays an important role in the activity of Mn3+-Pr.
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