Origins of Life and Evolution of Biospheres

, Volume 37, Issue 1, pp 61–65

The Viability of a Nonenzymatic Reductive Citric Acid Cycle – Kinetics and Thermochemistry

Article

Abstract

The likelihood of a functioning nonenzymatic reductive citric acid cycle, recently proposed as the precursor to biosynthesis on early Earth, is examined on the basis of the kinetics and thermochemistry of the acetate → pyruvate → oxaloacetate → malate sequence. Using data derived from studies of the Pd-catalyzed phosphinate reduction of carbonyl functions it is shown that the rate of conversion of pyruvate to malate with that system would have been much too slow to have played a role in the early chemistry of life, while naturally occurring reduction systems such as the fayalite–magnetite–quartz and pyrrhotite–pyrite–magnetite mineral assemblages would have provided even slower conversions. It is also shown that the production of pyruvate from acetate is too highly endoergic to be driven by a naturally occurring energy source such as pyrophosphate. It is thus highly doubtful that the cycle can operate at suitable rates without enzymes, and most unlikely that it could have participated in the chemistry leading to life.

Keywords

citric acid cycle nonenzymatic citrate kinetics 

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Copyright information

© Springer Science + Business Media B.V. 2006

Authors and Affiliations

  1. 1.US Geological SurveyMenlo ParkUSA
  2. 2.Palo AltoUSA

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