Chemical and catalytical properties of thermal polymers of amino acids (proteinoids)

The significance of thermal polyamino acids (proteinoids) as abiotic predecessors of proteins is reviewed on the basis of new experimental results. Most proteinoids yield only 50% to 80% amino acid upon acid hydrolysis. They contain 40% to 60% less peptide links than typical proteins, whereas their average nitrogen content is like that of proteins. The arrangement of amino acid residues is nonrandom. The degree of nonrandomness is difficult to determine because unusual crosslinks disturb most of the sequencing methods typically applied, in protein chemistry. The products obtained in a polymerization experiment are heterogeneous. They can be separated into a limited number of related fractions by chromatography or electrophoresis and other separation methods applied in protein chemistry. Their molecular weights are typically between 400 and 10 000. The number of free NH₂-groups, is usually smaller than in comparable proteins A significant fraction of NH₂-groups yields imidazole-type bases during the thermal polymerization. Optically active amino acids racemize during the same process. So far no helicity could be detected. Proteinoids are thus clearly distinct from proteins However, many of them exhibit weak catalytic activities and tend to undergo self-assembly into microstructures. Their properties of which only a few have been mentioned still support their role as possible candidates for ancestors of first proteins.