Hydrogen Drives Part of the Reverse Krebs Cycle under Metal or Meteorite Catalysis.

Hydrogen (H 2 ) is a geological source of reducing electrons that is thought to have powered the metabolism of the last universal common ancestor to all extant life, and that is still metabolized by various modern organisms. It has been suggested that H 2 drove a geochemical analogue of some or all of the reverse Krebs cycle at the emergence of the metabolic network, catalyzed by metals, but this has yet to be demonstrated experimentally. Herein, we show that three consecutive steps of the reverse Krebs cycle, converting oxaloacetate into succinate, can be driven without enzymes and in one-pot by H 2 as the reducing agent under mild conditions compatible with biological chemistry. Low catalytic amounts of nickel (10-20 mol %) or platinum group metals (0.1-1 mol %) or even small amounts of ground meteorites were found to promote the reductive chemistry at temperatures between 5 and 60 °C and over a wide pH range, including pH 7. These results lend additional support to the hypothesis that geologically produced hydrogen and metal catalysts could have initiated early metabolic networks.