Metabolic rate and directional nucleotide substitution in animal mitochondrial DNA

There is marked heterogeneity of nucleotide composition in mitochondrialDNA across divergent animals. Differences in nucleotide compositionpresumably reflect differences in directional nucleotide substitution forA+T or G+C nucleotides. In mitochondrial DNA, there is A+T directionalnucleotide substitution in most (if not all) animals surveyed, and themagnitude of directional A+T nucleotide substitution differs greatly withinand among groups. Differences in directional nucleotide substitution amonglineages of mammals can be explained by changes in metabolic physiology.This relationship is thought to be mediated by the effect of oxygenradicals because these toxic compounds are by-products of aerobicmetabolism and are known mutagens. Association between metabolism andnucleotide composition provides additional evidence in favor of thehypothesis that rates and patterns of nucleotide substitution inmitochondrial DNA can be influenced by factors that impinge on rates ofendogenous DNA damage.