Nitrite reductase activity of rat and human xanthine oxidase, xanthine dehydrogenase, and aldehyde oxidase: Evaluation of their contribution to NO formation in vivo

L.B. Maia, V. Pereira, L. Mira, J.J.G. Moura

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)

Abstract

Nitrite is presently considered a NO "storage form" that can be made available, through its one-electron reduction, to maintain NO formation under hypoxia/anoxia. The molybdoenzymes xanthine oxidase/dehydrogenase (XO/XD) and aldehyde oxidase (AO) are two of the most promising mammalian nitrite reductases, and in this work, we characterized NO formation by rat and human XO/XD and AO. This is the first characterization of human enzymes, and our results support the employment of rat liver enzymes as suitable models of the human counterparts. A comprehensive kinetic characterization of the effect of pH on XO and AO-catalyzed nitrite reduction showed that the enzyme's specificity constant for nitrite increase 8-fold, while the KmNO2- decrease 6-fold, when the pH decreases from 7.4 to 6.3. These results demonstrate that the ability of XO/AO to trigger NO formation would be greatly enhanced under the acidic conditions characteristic of ischemia. The dioxygen inhibition was quantified, and the KiO2 values found (24.3-48.8 μM) suggest that in vivo NO formation would be fine-tuned by dioxygen availability. The potential in vivo relative physiological relevance of XO/XD/AO-dependent pathways of NO formation was evaluated using HepG2 and HMEC cell lines subjected to hypoxia. NO formation by the cells was found to be pH-, nitrite-, and dioxygen-dependent, and the relative contribution of XO/XD plus AO was found to be as high as 50%. Collectively, our results supported the possibility that XO/XD and AO can contribute to NO generation under hypoxia inside a living human cell. Furthermore, the molecular mechanism of XO/AO-catalyzed nitrite reduction was revised. (Chemical Equation Presented). © 2014 American Chemical Society.
Original languageEnglish
Pages (from-to)685-710
Number of pages26
JournalBiochemistry
Volume54
Issue number3
DOIs
Publication statusPublished - 27 Jan 2015

Keywords

  • FREE-RADICAL GENERATION
  • MOLYBDENUM ENZYMES
  • HUMAN LIVER
  • ISCHEMIA-REPERFUSION
  • SYNTHASE ACTIVITY
  • AQUEOUS-SOLUTION
  • HALF-REACTION
  • RABBIT LIVER
  • NADH OXIDASE
  • OXIDOREDUCTASE ACTIVITY

Fingerprint

Dive into the research topics of 'Nitrite reductase activity of rat and human xanthine oxidase, xanthine dehydrogenase, and aldehyde oxidase: Evaluation of their contribution to NO formation in vivo'. Together they form a unique fingerprint.

Cite this