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黄嘌呤氧化还原酶催化亚硝酸盐还原为一氧化氮。

Reduction of nitrite to nitric oxide catalyzed by xanthine oxidoreductase.

作者信息

Godber B L, Doel J J, Sapkota G P, Blake D R, Stevens C R, Eisenthal R, Harrison R

机构信息

Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.

出版信息

J Biol Chem. 2000 Mar 17;275(11):7757-63. doi: 10.1074/jbc.275.11.7757.

Abstract

Xanthine oxidase (XO) was shown to catalyze the reduction of nitrite to nitric oxide (NO), under anaerobic conditions, in the presence of either NADH or xanthine as reducing substrate. NO production was directly demonstrated by ozone chemiluminescence and showed stoichiometry of approximately 2:1 versus NADH depletion. With xanthine as reducing substrate, the kinetics of NO production were complicated by enzyme inactivation, resulting from NO-induced conversion of XO to its relatively inactive desulfo-form. Steady-state kinetic parameters were determined spectrophotometrically for urate production and NADH oxidation catalyzed by XO and xanthine dehydrogenase in the presence of nitrite under anaerobic conditions. pH optima for anaerobic NO production catalyzed by XO in the presence of nitrite were 7.0 for NADH and </=6.0 for xanthine. Involvement of the molybdenum site of XO in nitrite reduction was shown by the fact that alloxanthine inhibits xanthine oxidation competitively with nitrite. Strong preference for Mo=S over Mo=O was shown by the relatively very low NADH-nitrite reductase activity shown by desulfo-enzyme. The FAD site of XO was shown not to influence nitrite reduction in the presence of xanthine, although it was clearly involved when NADH was the reducing substrate. Apparent production of NO decreased with increasing oxygen tensions, consistent with reaction of NO with XO-generated superoxide. It is proposed that XO-derived NO fulfills a bactericidal role in the digestive tract.

摘要

黄嘌呤氧化酶(XO)已被证明在厌氧条件下,以NADH或黄嘌呤作为还原底物时,能催化亚硝酸盐还原为一氧化氮(NO)。通过臭氧化学发光直接证明了NO的产生,并且显示出与NADH消耗的化学计量比约为2:1。以黄嘌呤作为还原底物时,由于NO诱导XO转化为相对无活性的脱硫形式导致酶失活,使得NO产生的动力学变得复杂。在厌氧条件下,在亚硝酸盐存在的情况下,通过分光光度法测定了XO和黄嘌呤脱氢酶催化尿酸产生和NADH氧化的稳态动力学参数。在亚硝酸盐存在下,XO催化厌氧NO产生的最适pH值,以NADH为底物时为7.0,以黄嘌呤为底物时≤6.0。异黄嘌呤与亚硝酸盐竞争性抑制黄嘌呤氧化,这一事实表明XO的钼位点参与了亚硝酸盐还原。脱硫酶显示出相对非常低的NADH-亚硝酸盐还原酶活性,表明对Mo=S的偏好远高于Mo=O。尽管当NADH为还原底物时FAD位点明显参与其中,但在黄嘌呤存在的情况下,XO的FAD位点并未显示出对亚硝酸盐还原有影响。随着氧张力的增加,NO的表观产生量下降,这与NO与XO产生的超氧化物反应一致。有人提出,XO衍生的NO在消化道中发挥杀菌作用。

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