A Computational Study of a Prebiotic Synthesis of a Tripeptide: Thyrotropic Releasing Hormone (TRH)

Abstract

Ab initio calculations are used to calculate the viability of a prebiotic mechanism for the synthesis of L-proteins considered as a one-dimensional cooperative system having interlocking terms involving two neighbouring amino-acid residues yielding the inter-bond energy, optimum conformation, and charge distribution leading to an estimate of the secondary structure. The prebiotic synthesis of poly amino acids is illustrated with the synthesis of a tripeptide, thyrotropic releasing hormone. The magnesium ion metalloporphyrin complex is shown to bind the prebiotic stereospecific ligand precursors of the amino acids proline, histidine, and pyroglutamic on the metal or nitrogen pyrrole sites as a two-site catalyst in their copolymerization to form Glu-His-Pro-NH2. The order of addition of the monomers is the reverse of pyroglutamylhistidinylprolamide to form the tripeptide. which is separated from the catalyst by hydrogen ions. The reactions are feasible from the overall enthalpy changes in the ZKE approximation at the HF and MP2 /6-31G* level, and with acceptable activation energies.