铁对黄嘌呤氧化酶依赖性抗坏血酸氧化的刺激作用的动力学研究。

A kinetic study on iron stimulation of the xanthine oxidase dependent oxidation of ascorbate.

作者信息

Løvstad Rolf A

机构信息

Department of Medical Biochemistry, Institute of Basic Medical Sciences, University of Oslo, PO Box 1112 Blindern, N-0317 Oslo, Norway.

出版信息

Biometals. 2003 Sep;16(3):435-9. doi: 10.1023/a:1022523920998.

DOI:10.1023/a:1022523920998

PMID:12680706

Abstract

Xanthine oxidase reduces molecular oxygen to H2O2 and superoxide radicals during its catalytic action on xanthine, hypoxanthine or acetaldehyde. Ascorbate is catalytically oxidized by the superoxide radicals generated, when present in the reaction solution (Nishikimi 1975). The present study shows that iron ions markedly stimulate the enzyme dependent ascorbate oxidation, by acting as a red/ox-cycling intermediate between the oxidase and ascorbate. An apparent Km-value of 10.8 microM characterized the iron stimulatory effect on the reaction at pH 6.0. Reduced transition-state metals can be oxidized by H2O2 through a Fenton-type reaction. Catalase was found to reduce the effect of iron on the enzyme dependent ascorbate oxidation, strongly suggesting that H2O2, produced during catalysis, is involved in the oxidation of ferrous ions.

摘要

黄嘌呤氧化酶在对黄嘌呤、次黄嘌呤或乙醛的催化作用过程中，将分子氧还原为过氧化氢和超氧自由基。当反应溶液中存在抗坏血酸时，它会被生成的超氧自由基催化氧化（西木见，1975年）。本研究表明，铁离子通过作为氧化酶和抗坏血酸之间的氧化还原循环中间体，显著刺激依赖酶的抗坏血酸氧化。在pH 6.0时，铁对该反应的刺激作用的表观Km值为10.8微摩尔。还原态的过渡金属可通过芬顿型反应被过氧化氢氧化。已发现过氧化氢酶可降低铁对依赖酶的抗坏血酸氧化的影响，这强烈表明催化过程中产生的过氧化氢参与了亚铁离子的氧化。