How oxygen changed metabolism

Metabolic networks come in just four basic types, according to a bioinformatics study in this week?s Science, which also shows that oxygen is required for the largest and most complex networks. The enzymatic reactions that take place in oxygen-dependent networks evolved after molecular oxygen appeared on Earth around 2.2 billion years ago, and some of these adaptations may have been important in a subsequent explosion of multicellular life, according to the authors. "It is an intriguingly fresh approach to the whole problem of biochemical complexity," said Joseph Kirschvink of the California Institute of Technology in Pasadena, who was not involved in the study. Previous work by first author Jason Raymond of Lawrence Livermore National Laboratory in California revealed that, in aerobic organisms, many anoxic enzymatic reactions were replaced with new reactions and enzymes. To see if this finding held true for entire metabolic pathways, Raymond and co-author Daniel Segrè of ...