Polypeptide formation by heating aqueous solution of amino acids and peptides

Abstract

It is considered that there were several possible pathways in which polypeptides were produced on premitive earth. Of these pathways, (i) condensation of solid amino acids on heating, (2) condensation of amino acids in aqueous media over condensing agents or (3) on heating are known. The first one has been studied in detail(Fox et al., 1960). The second one has not given longer peptides than 5 residues(Hulshof et al., 1976). However, there are a few reports related to the third one in which much larger peptides were obtained from aspargine with the molecular weight more than c.a. 3000(Kovacs et al., 1961.; Harada et al., 1978). In this paper, we wish to describe the role of aspargine and glutamine having 8 or y primary amide for polypeptide formation in the hypothetical premitive ocean. We carried out the heating of aqueous solution contaning aspargine and other amino acids(glycine, alanine, and valine) or peptides which have asparagine or glutamine residue in the C-terminal. Heatin @ reaction of aqueous solution of as~arqine and some other amino acids. Five mmol L-aspargine monohydrate(750mg) and other amino acids[0.5-2.5 mmol(Gly, Ala, Val)]were dissolved in 5 ml H20 , and the solutions sealed in vacuo in a glass tube were heated at 120°C for 2-200 hr. After the reactions, the reaction solution was analyzed by amino acid analyzer and remaining sample was loaded into a Sephadex G-15 column. The elution was carried out with 0.5 M-acetic acid to give white amorophous powder. The 32 hours' reaction mixtures gave muximum isolated yield(>90mg). The IR of this compound showed typical acidic polypeptide absorption(1710, 1650, 1540 cm-l). Averaged molecular weight of this peptide was estimated to be 1500-3000 by gel filtration. Molar composition of the amino acids contained in the copolyamino acids were almost pallarel to the first composition of the reaction mixtures, when the molar ratio of other amino acid to L-aspargine was lower than 50 %. Heating reactions of amino acid solutions without aspargine