The room temperature potentiometry of xanthine oxidase. pH-dependent redox behavior of the flavin, molybdenum, and iron-sulfur centers.
作者： A G Porras , G Palmer
DOI: 10.1016/S0021-9258(18)33807-9
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摘要: A series of potentiometric titrations xanthine oxidase have been performed at room temperature in the pH range 6.1-9.9. Reduction two Fe/S centers was monitored by CD, and that FAD Mo center EPR. The behave as having a protonable group whose pKa changes with reduction state (E = -344 mV, pKo 6.4, pKr 8.1 for I; E -249 8.0 II). flavin types molybdenum show varying behavior, but, all cases, electron addition is accompanied protonation. sequence reduction, protonation, protonation E1 -398 E2 -240 pK1 9.5, pK2 7.4. For "rapid" molybdenum, -369 -301 7.9, 8.4; slow 320 -477 7.5, 9.5. Comparison to data obtained previously cryogenic temperatures (Cammack, R., Barber, M. J., Bray, R. C. (1976) Biochem. J. 157, 469-468 Seigel, L. (1982) Flavins Flavoproteins (Massey, V., Williams, H., eds) pp. 796-804, Elsevier/North-Holland, New York) showed significant dependence, which calls re-evaluation conclusions reached using techniques (e.g. rapid-freeze). optical absorbance characteristics enzyme were also investigated possible suggested.
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