Nitric oxide and peroxynitrite cause irreversible increases in the K(m) for oxygen of mitochondrial cytochrome oxidase: in vitro and in vivo studies.
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 K(m) 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 K(m). These include: treatment of the purified enzyme with peroxynitrite or high (microM) 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.
Cooper
Chris E
CE
Department of Biological Sciences, University of Essex, Central Campus Wivenhoe Park, Essex CO4 3SQ, Colchester, UK. ccooper@essex.ac.uk
Davies
Nathan A
NA
Psychoulis
Minas
M
Canevari
Laura
L
Bates
Tim E
TE
Dobbie
Michael S
MS
Casley
Christopher S
CS
Sharpe
Martyn A
MA
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors; D005849:Gerbillinae; D008928:Mitochondria / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D008954:Models, Biological; D009569:Nitric Oxide / Q000737:chemistry / Q000494:pharmacology*; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D030421:Peroxynitrous Acid / Q000737:chemistry / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D003576:Electron Transport Complex IV; D010100:Oxygen