Author/Editor		Schara, M; Nemec, M; Pečar, S
Title		The involvement of uric acid in the scavenging of nitroxide radicals by ascorbate
Type		članek
Source		Acta Chim Slov
Vol. and No.		Letnik 47
Publication year		2000
Volume		str. 39-46
Language		eng
Abstract		The reaction kinetics, measured by electron paramagnnetic resonance (EPR) was used to study the involvement of uric acid in the reactions of nitroxide radical (TEMPONE) scavening by ascorbate (PBS, pH 7.4 and T=37 degreece). In absence of iron ions, the oxygen reoxidation of hydroxylamine was slow and the addition of uric acid did not change the observed kinetics. On the other hand, in presence of iron ions the reoxidation starts to recover the nitroxide radical. This reaction rate is strongly enhanced by uric acid. In fact there are two hypotheses, the first ascribes more efficient iron complexes with uric acid, by which the reoxidation rate increases. Especially the competition between the phosphate and uric acid ligands might be important. Howevwr, uric acid could be directly involved in scavening the hydroxyl radicals, and herewith influence the reaction rate. No scavening activity of uric acid in UV irradiated aqueous solutions was found. The trapped adducts of the hydroxyl and the superoxide radicals show the same concentration in presence and absence of uric acid.
Summary		Raziskali smo vpliv sečne kisline na kinetiko redukcije nitroksidnih radikalov z askorbatom. Uporabili smo metodo elektronske paramagnetne resonance (EPR) in spinski označevalec TEMPON. Reakcije so potekale v PBS oziroma Tris-HCl pufru pri pH 7,4 in T= 37 stopinj C. V odsotnosti železovih ionov je bila reoksidacija hidroksilamina počasna in dodatek sečne kisline ni povzročil sprememb hitrosti reakcije. V prisotnosti železovih ionov je reoksidacija hitrejša, prisotnost sečne kisline pa bistveno pospeši reoksidacijo hidroksilamina. Dejansko sta tu dve možnosti in sicer, da sečna kislina tvori železov kompleks, ki je bolj aktiven v smislu hitrosti redoks reakcije-reoksidacije kot železovi fosfati, oziroma da sečna kislina mimo tega posega v hitrost reakcije neposredno. Glede na poskus v Tris -HCl pufru, kjer pospeševalnega efekta sečne kisline ni, je prva hipoteza bolj verjetna. To potrjujeta tudi oba poskusa s spinskimi lovilci, kjer ni bilo opaziti vpliva sečne kisline na tvobo kisikovih radikalov, z vzbujanjem tvorbe kisikovih radikalov s Fentonovo reakcijo, oziroma z obsevanjem z UV žarki.
Descriptors		URIC ACID NITROUS OXIDE FREE RADICAL SCAVENGERS ASCORBIC ACID ELECTRON SPIN RESONANCE SPECTROSCOPY IRON KINETICS TROMETHAMINE