ALTERNATIVE OXIDASE - FROM GENE TO FUNCTION

Plants, some fungi, and protists contain a cyanide-resistant, alternat ive mitochondrial respiratory pathway. This pathway branches at the ub iquinone pool and consists of an alternative oxidase encoded by the nu clear gene Aox1. Alternative pathway respiration is only linked to pro ton translocation at Complex 1 (NADH dehydrogenase). Alternative oxida se expression is influenced by stress stimuli-cold, oxidative stress, pathogen attack-and by factors constricting electron flow through the cytochrome pathway of respiration. Control is exerted at the levels of gene expression and in response to the availability of carbon and red ucing potential. Posttranslational control involves reversible covalen t modification of the alternative oxidase and activation by specific c arbon metabolites. This dynamic system of coarse and fine control may function to balance upstream respiratory carbon metabolism and downstr eam electron transport when these coupled processes become imbalanced as a result of changes in the supply of, or demand for, carbon, reduci ng power, and ATP.