A protective function of the coacervates against UV light on the primitive Earth

Abstract

Results from simulation experiments in the laboratory support the Oparin–Haldane hypothesis of chemical evolution^1–4. The organic compounds produced may have accumulated in the primitive sea, constituting the so-called ‘primordial soup’ of organic molecules. Beyond this primordial stage, however, many developments were required before the emergence of the first cellular organism. The first cell need not necessarily have been a modern cell, complete with a membrane, a chromosome, ribosomes, enzymes, a metabolism, and the property of self-replication; the primary requirement of the protocell would have been the ability to evolve into a complete cell. There are many models of the protocell: for example coacervate droplets^5–9, proteinoid microspheres^10,11, micelles (lipid vesicles)¹², and marigranules^13,14. Of these, the coacervate droplets are of interest as they are dynamic^6,7 and because their mechanism of formation is perhaps better understood^15–16. Coacervate droplets are essentially small bounded spaces in which the concentration of substances is higher than in the surrounding medium and in which the distribution of the substances differs from that in the solutions. Their essential functions in the protocell model are: (1) selection; (2) concentration; (3) production of hypohydrous effects; (4) interaction; and (5) organization^5–9. Here we report another possible function of the coacervate. We added glycine or diglycine to the coacervate system, then irradiated the system with an argon lamp. We report that the coacervate droplets concentrated glycine or diglycine, thus protecting them from decomposition by irradiation. These results suggest a protective function of the coacervate against UV light on the primitive Earth.