Astrobiology Workshop, Macquarie University July 12-13 2001

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Metabolic diversity in hyperthermophiles and implications for the origin of life

Hugh Morgan ( Dept of Biological Sciences, University of Waikato, New Zealand)

Cellular life is a complex of metabolic pathways. The rudiments of metabolism must have preceded the advent of cellular life. Glycolysis is universally distributed in a conserved manner in all branches of the tree of life and might represent the primordial metabolic flux. Recent hypotheses focus on an autotrophic origin of life, with fixed CO2 being channeled through glycolytic intermediates in the gluconeogenic direction.

Phosphofructokinase (PFK) is a key enzyme of the glycolytic pathway, but when ATP is used as phophoryl and energy source the reaction occurs in the forward direction and is essentially irreversible. PFK enzymes which use either pyrophosphate (PPi) or polyphosphate (polyP) instead of ATP have been described, and catalyze a fully reversible reaction. PPi and PolyP occur naturally in geothermal waters and could provide a renewable energy source for autotrophic metabolism.

We have investigated the phylogeny of PFK enzymes from all three domains of life to determine if the PPi-PFK variants represent "ancient" forms of the enzyme. The results present a more complex phylogeny for this activity than previously thought. The diversity of PFK types will be discussed and their distribution in hyperthermophiles illustrated in relation to the tree of life.