Catalysis of peptide bond formation by histidyl-histidine in a fluctuating clay environment

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.