Metabolic Rate and Longevity - Not Linear

While one might think that metabolic rate and longevity are linked - run faster, wear out faster - that isn't the case. Nothing is ever simple in biology, and the actual situation points once more to the significance of mitochondrial free radical generation: "In animals, longevity (maximal lifespan) is inversely related to mass-specific basal metabolic rates. However, contrary to expectation, in several mammalian taxa, exceptional longevity is associated with high basal metabolic rate, and also fast evolution of mtDNA-coded proteins. The association of these traits was suggested to result from adaptive selection of mutations in mtDNA coded proteins, which accelerates basal respiration, thus inhibiting the generation of reactive oxygen species that constrain longevity. In Serinus, a genus of finches (canaries) that exhibits the highest rate of cytochrome b evolution, and the highest values of exceptional longevity and lifetime expenditure of energy in all birds, many of the substitutions in cytochrome b are clustered around Q(i), a ubiquinone binding site adjacent to the mitochondrial matrix, apparently selected to increase the rate of ubiquinone reduction. We therefore suggest that, in songbirds, the accelerated evolution of cytochrome b involved selection of mutations that reduce the generation of reactive oxygen species, thus contributing to the evolution of exceptional longevity."

Link: http://www.ncbi.nlm.nih.gov/pubmed/17562891

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