Marigranules, highly organized particles of 0.3 to 2.5μm in diameter, were produced from a reaction of glycine and acidic, basic, and aromatic amino acids at 105°C for 8 weeks under a N₂ atmosphere in a modified sea medium enriched with six essential transition elements. The resulting marigranules were purified by centrifugation in ascending concentrations of Ficoll 400 (5 to 20%). The marigranules (C, 58.22; H, 3.76; N, 14.23; ash, 7.62%) were ununiformly packed with KOH-soluble polymers and they also had membrane-like structures. Their infrared spectrum suggested the presence of peptide bonds. The interior structure of marigranules was solubilized by treatment with KOH solution. The KOH-solubilized component was characterized by gel filtration and polyacrylamide gel electrophoresis. The component consisted of polymers with molecular weights of 1, 800, 6, 800, 15, 000, and 82, 000 daltons, and 34% of the total nitrogen was revealed as primary amino groups after treatment with elastase. This suggests that the polymers have at least one peptide bond per three amino acid residues. Thus, it appears that the interior of marigranules consists of polymers with an elastin-like structure. The surface structure of marigranules was solubilized with SDS and Triton X-100. The SDS-solubilized components were 3, 400, 350, and 150 daltons in size.
We found that organized particles were phase-separated from a concentrated aqueous solution of freeze-dried powder prepared from the reaction mixture mentioned above, and we called the particles marisomes. Marisomes (C, 63.67; H, 6.71; N, 10.56; ash, 6.54%) had a spherical structure of 2 to 3μm in diameter. They were found to be empty particles with a soft envelope by scanning electron microscopic observation. Marisomes were completely solubilized by SDS, ethanol, and Triton X-100. The solubilized marisomes were phase-separated again by dialysis against water. Marisomes were also solubilized in boiling water and were phase-separated again on cooling. Thus the system was reversible. Marisomes mainly consisted of lipophilic polymers with molecular weights of approx. 3, 400 daltons. The molecular size and lipophilic properties of marisomes were quite similar to those of the surface structure of marigranules.
Taking into consideration the characteristics of both the particles, we were led to the working hypothesis that a may be the precursor of a marigranule, that is, the was first phase-separated from the reaction mixture and then amino acids and their oligomers were absorbed into the , in which they were polymerized to give elastin-like polymers with cross-links. Thus, both the organized particles, marisomes and marigranules, were good models for the course of evolution of protocells. In addition, the modified sea medium proved to be a good simulative marine environment for studies of chemical evolution in the primeval sea.

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