On the chemical diversity of the prebiotic ocean of early Earth

This work investigates the consequences on the diverse number of chemical species in a pre-biotic terrestrial aqueous environment endowed with an amino acid source induced by the spontaneous build-up of catalytically active polypeptides from amino acid monomers. The assumed probability that a randomly formed polypeptide exhibits catalytic properties is dependent on constraining both the chemical identity and the position of a fraction of the amino acid residues.Within this hypothesis, and using values of the average length n of the catalytic polypeptides about one half of the present-day enzymes, the stationary-state concentration of the catalytically active polypeptides is &10−30−10−19 M, and the ratio of the concentration of a product of a catalytic process to the initial concentration of the corresponding substrate is predicted to be &10−6−105. Matching the mean life of each catalytic polypeptide to the mean life of its substrate (λ&ω) is only possible by significantly raising the intensity of the source of the amino acid monomers. Under these hypothetical optimal conditions, the mean lives of the catalytic polypeptides and their substrates have values ω−1&λ−1&10 yr and the asymptotic concentration of each product is of the same order of magnitude as the concentration of the substrate. In all cases the catalytic efficiency necessary to form the active peptides takes the typical values of present-day enzymes.