The condensation of glycine to form oligoglycines during wet-dry fluctuations on clay surfaces was enhanced up to threefold or greater by small amounts of histidyl-histidine. In addition, higher relative yields of the longer oligomers were produced. Other specific dipeptides tested gave no enhancement, and imidazole, histidine, and N-acetylhistidine gave only slight enhancements. Histidyl-histidine apparently acts as a true catalyst (in the sense of repeatedly catalyzing the reaction), since up to 52 nmol of additional glycine were incorporated into oligoglycine for each nmol of catalyst added. This is the first known instance of a peptide or similar molecule demonstrating a catalytic turnover number greater than unity in a prebiotic oligomer synthesis reaction, and suggests that histidyl-histidine is a model for a primitive prebiotic protoenzyme. Catalysis of peptide bond synthesis by a molecule which is itself a peptide implies that related systems may be capable of exhibiting autocatalytic growth.

Summary. The condensation of glycine to form oligoglycine during temperature and moisture fluctuations on clay surfaces was enhanced up to fourfold by polyribonucleotides. Polydeoxyribonucleotides gave no enhancement. Yields were greatly reduced in the absence of clay. A small preference was observed among the polyribonucleotide bases with enhancements in the order of Poly G > Poly A = Poly U > Poly C at high density of polynucleotide on the clay surface and Poly G > Poly U > Poly C > Poly A at low density. This and other experiments seem to indicate a codonic bias in the interaction of polynucleotides with amino acids reacting to form peptide bonds. A mechanism is proposed which involves (1) activation of glycine on the clay surface, (2) formation of esters between glycine and the 2'-OH groups of the polyribonucleotide, and (3) formation of peptide bonds between adjacent amino acyl esters. If this mechanism is correct, it may provide the basis for a simple, direct-template translation process.

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