Nitric oxide and peroxynitrite cause irreversible increases in the Km for oxygen of mitochondrial cytochrome oxidase: in vitro and in vivo studies

https://doi.org/10.1016/j.bbabio.2003.08.003Get rights and content
Under an Elsevier user license
open archive

Abstract

Mitochondrial cytochrome oxidase is competitively and reversibly inhibited by inhibitors that bind to ferrous heme, such as carbon monoxide and nitric oxide. In the case of nitric oxide, nanomolar levels inhibit cytochrome oxidase by competing with oxygen at the enzyme's heme–copper active site. This raises the Km for cellular respiration into the physiological range. This effect is readily reversible and may be a physiological control mechanism. Here we show that a number of in vitro and in vivo conditions result in an irreversible increase in the oxygen Km. These include: treatment of the purified enzyme with peroxynitrite or high (μM) levels of nitric oxide; treatment of the endothelial-derived cell line, b.End5, with NO; activation of astrocytes by cytokines; reperfusion injury in the gerbil brain. Studies of cell respiration that fail to vary the oxygen concentration systematically are therefore likely to significantly underestimate the degree of irreversible damage to cytochrome oxidase.

Keywords

Cytochrome c oxidase
Nitric oxide
Mitochondria
Km
Oxygen
Peroxynitrite

Abbreviations

DTPA
diethylenetriaminepentaacetic acid
PTIO
2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide
TMPD
(N,N,N′,N′-tetramethyl-p-phenylenediamine hydrochloride)

Cited by (0)

1

Present address: Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, Oxford, Oxon OX3 9D, UK.