Respiratory chains in the last common ancestor of living organisms

Sequences in current databases show that a number of proteins involved in r espiratory processes are homologous in archaeal and bacterial species. In p articular, terminal oxidases belonging to oxygen, nitrate, sulfate, and sul fur respiratory pathways have been sequenced in members of both domains. Th ey include cytochrome oxidase, nitrate reductase, adenylylsulfate reductase , sulfite reductase, and polysulfide reductase. These proteins can be assig ned to the last common ancestor of living organisms assuming that the deepe st split of the three domains of life occurred between Archaea and Bacteria and that they were not acquired through lateral gene transfer by one of th ese domains. These molecular data indicate that several of the most importa nt respiratory pathways arose early in evolution and that the last common a ncestor of living organisms was not a simple organism in its energetic meta bolism. Rather, it may have been able to gain energy by means of at least f our electron transport chains, and therefore it may have been prepared to f ace a wide range of environmental conditions.