Characterization of oxidative phosphorylation in the colorless chlorophyte Polytomella sp. Its mitochondrial respiratory chain lacks a plant-like alternative oxidase.
The presence of an alternative oxidase (AOX) in Polytomella sp., a colorless relative of Chlamydomonas reinhardtii, was explored. Oxygen uptake in Polytomella sp. mitochondria was inhibited by KCN (94%) or antimycin (96%), and the remaining cyanide-resistant respiration was not blocked by the AOX inhibitors salicylhydroxamic acid (SHAM) or n-propylgallate. No stimulation of an AOX activity was found upon addition of either pyruvate, alpha-ketoglutarate, or AMP, or by treatment with DTT. An antibody raised against C. reinhardtii AOX did not recognized any polypeptide band of Polytomella sp. mitochondria in Western blots. Also, PCR experiments and Southern blot analysis failed to identify an Aox gene in this colorless alga. Finally, KCN exposure of cell cultures failed to stimulate an AOX activity. Nevertheless, KCN exposure of Polytomella sp. cells induced diminished mitochondrial respiration (20%) and apparent changes in cytochrome c oxidase affinity towards cyanide. KCN-adapted cells exhibited a significant increase of a-type cytochromes, suggesting accumulation of inactive forms of cytochrome c oxidase. Another effect of KCN exposure was the reduction of the protein/fatty acid ratio of mitochondrial membranes, which may affect the observed respiratory activity. We conclude that Polytomella lacks a plant-like AOX, and that its corresponding gene was probably lost during the divergence of this colorless genus from its close photosynthetic relatives.
Reyes-Prieto
Adrián
A
Departamento de Genética Molecular, Instituto de Fisiologi;a Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-243, 04510, México, D.F., Mexico.
El-Hafidi
Mohammed
M
Moreno-Sánchez
Rafael
R
González-Halphen
Diego
D
D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000460:Chlorophyta / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D010085:Oxidative Phosphorylation; D010088:Oxidoreductases / Q000378:metabolism*; D010101:Oxygen Consumption; D010940:Plant Proteins; D000099188:Alternative Oxidase
D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV; D005227:Fatty Acids; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D000099188:Alternative Oxidase