Oxidative phosphorylation supported by an alternative respiratory pathway in mitochondria from Euglena.
The effect of antimycin, myxothiazol, 2-heptyl-4-hydroxyquinoline-N-oxide, stigmatellin and cyanide on respiration, ATP synthesis, cytochrome c reductase, and membrane potential in mitochondria isolated from dark-grown Euglena cells was determined. With L-lactate as substrate, ATP synthesis was partially inhibited by antimycin, but the other four inhibitors completely abolished the process. Cyanide also inhibited the antimycin-resistant ATP synthesis. Membrane potential was collapsed (<60 mV) by cyanide and stigmatellin. However, in the presence of antimycin, a H(+)60 mV) that sufficed to drive ATP synthesis remained. Cytochrome c reductase, with L-lactate as donor, was diminished by antimycin and myxothiazol. Cytochrome bc(1) complex activity was fully inhibited by antimycin, but it was resistant to myxothiazol. Stigmatellin inhibited both L-lactate-dependent cytochrome c reductase and cytochrome bc(1) complex activities. Respiration was partially inhibited by the five inhibitors. The cyanide-resistant respiration was strongly inhibited by diphenylamine, n-propyl-gallate, salicylhydroxamic acid and disulfiram. Based on these results, a model of the respiratory chain of Euglena mitochondria is proposed, in which a quinol-cytochrome c oxidoreductase resistant to antimycin, and a quinol oxidase resistant to antimycin and cyanide are included.
Moreno-Sánchez
R
R
Departamento de Bioquímica, Instituto Nacional de Cardiología, Juan Badiano # 1, Col. Sección XVI, Tlalpan, Mexico, Mexico. morenosanchez@hotmail.com
Covián
R
R
Jasso-Chávez
R
R
Rodríguez-Enríquez
S
S
Pacheco-Moisés
F
F
Torres-Márquez
M E
ME
D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D019069:Cell Respiration / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005055:Euglena / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism; D008689:Methacrylates; D008928:Mitochondria / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000378:metabolism; D010085:Oxidative Phosphorylation / Q000187:drug effects; D011090:Polyenes / Q000494:pharmacology; D012966:Sodium Cyanide / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology
D008689:Methacrylates; D011090:Polyenes; D013844:Thiazoles; C032456:antimycin; D019344:Lactic Acid; D000968:Antimycin A; C030517:myxothiazol; D000255:Adenosine Triphosphate; C041573:stigmatellin; D009245:NADH Dehydrogenase; D012966:Sodium Cyanide