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A number of species are known in which pyrophosphate is used in place of ATP for some of the housekeeping enzymes of metabolism. Pyrophosphates derived from volcanic gasses and dissolved in the earliest ocean as orthophosphate could-when recharged by protons to pyro- and tri-phosphate in a hydrothermal mound-have constituted the main energy storage molecules at an early period in evolution of life, before the advent of nucleic acids and their encoding of amino acids. Triphosphates have been shown to phosphorylate glycines and other amino acids in the laboratory to form cyclic acylphosphoramidates that react with further amino acids to produce dipeptides. The dipeptides then react with such cyclic acylphosphoramidates to generate tripeptides and so on, forming higher oligopeptides. Sequence-independent glycine-rich oligopeptides of eight or more residues are surmised to adopt a conformation in the presence of pyro- and tri-phosphate that both binds them and acts enzymically to catalyze their interconversions with phosphates and pyrophosphates. Oligopeptides and pyro/triphosphates are potentially synergistic as they encourage each other's synthesis. This synergy would have been a key feature of this early stage in evolution before the advent of the ribosome. A hydrothermal mound forming over a hottish (=100ºC) alkaline (pH 10-11) spring at the bottom of the carbonic and thereby acidulous (PH 5.5-6) Hadean Ocean affords an appropriate setting for this synergy. The peptide-bound phosphate molecules became arranged in inorganic membranes comprising the outer margins of the hydrothermal mound in such a way that the protons needed for this reaction come from outside of the existing large pH gradient across an inorganic divide, driving pyro/triphosphate, and hence also oligopeptide, synthesis.
|Glasgow Author(s) Enlighten ID:||Milner-White, Professor E|
|Authors:||Milner-White, E.J., and Russell, M.J.|
|College/School:||College of Medical Veterinary and Life Sciences|
|Journal Name:||Journal of Cosmology and Astroparticle Physics|
|Published Online:||01 January 2010|