Response to comments on thermal polypeptides by P. A. Temussi et al

Formation of specific amino acid sequences during thermal polymerization of amino acids

The mechanism of the thermal polymerization (at 180 degrees C) of glutamic acid, tyrosine, and glycine has been studied. Glutamic acid is quickly and almost completely converted into pyroglutamic acid. The only dipeptide that is formed by dimerization of the remaining two amino acids is cyclic glycyl-tyrosine (a diketopiperazine). In a secondary reaction pyroglutamic acid interacts with cyclic glycyl-tyrosine and yields pyroglutamyl-glycyl-tyrosine and pyroglutamyl-tyrosyl-glycine. Other di- or tripeptides are not observed. The preferential appearance of the two pyroglutamyl-peptides has been reported earlier by Nakashima et al. (1977). The present data explain those results. Model experiments show that cyclic glycyl-tyrosine can also be cleaved by other acids or bases. In the presence of acetic acid at 118 degrees C N-acetyl-glycyl-tyrosine is the major product. Partial hydrolysis predominantly yields tyrosyl-glycine. These effects are explained by stereospecific interactions. The results on self-ordering of amino acids during peptide formation are discussed in respect of the origin of prebiotic enzymes and genetic information.

Biotin. Its place in evolution

In the previous article we try to give an explanation for the success of models of enzymatic reactions in which coenzymes play a role. However, one vital cofactor that has thus far not yielded appreciably to this approach is biotin. We attempt to show that biotin presents a fundamentally new sort of problem to bioorganic chemistry; this problem requires consideration both of the origin of life and subsequent evolution in any attempt to understand the anomalies offered by this cofactor.