Enzymatic characterization of peptidic materials isolated from aqueous solutions of ammonium cyanide (pH 9) and hydrocyanic acid (pH 6) exposed to ionizing radiation

Abstract

The enzymatic digestion of some radiolytically produced peptidic materials was examined. The substrates were compounds isolated from 0.1 molar solutions of NH4CN (pH 9) and HCN (pH 6), after their exposure to gamma rays from a 60Co source (15-20 Mrad doses). Commercial proteolytic enzymes pronase and aminopeptidase M were used. The examined materials were of composite nature and proteolytic action was systematically observed after their subsequent purification. In some fractions the effect was found to be positive with up to 30% of peptide bonds cleaved with respect to the amino acid content. These findings support our previous conclusions on the free radical induced formation of peptidic backbones without the intervention of amino acids. Some side effects were also noted which might be of interest in observations on enzymatic cleavage of other composite peptidic materials of abiotic origin.

Radiolysis of aqueous solutions of hydrogen cyanide (pH∼6): Compounds of interest in chemical evolution studies

“…It might be worth mentioning at on the same occasion carbamyl glycinonitrile was ~o identified in the neutral fraction of irradiated an~m~ cyanide (in the fraction NUS44, 3% of the total mixture, Dragani6 et al 1980). The details will be Presented elsewhere (Niketid 1982 …”

“…However, it also shows that tee amounts and tee tYP es of radiolytic products depend to some extent on P~ The purpose of this work: was to examine in more det~ the radiolytic products of interest in chemical evolutiO~ studies at a natural pH (about 6) and to compare thegn with the earlier findings at pH 9 (Dragani~ et al 1980;Niketid et at. 1982).…”

Radiation chemistry of overirradiated aqueous solutions of hydrogen cyanide and ammonium cyanide

“…A positive test, however, does not necessarily mean that absorbance is a direct measure of peptide bonds. For a reliable evaluation, the amount of amino acids released on acid hydrolysis and their origins have to be considered also, as well as the enzymatic digestion (Niketi6 et al 1982). Figure 4 summarizes the biuret test data: characteristic absorption spectra at different doses ( Dragani6 el al.…”

“…5) suggests that the absorbances of the biuret complex are much stronger than would be expected from the amino acid contents (molar absorptivity of the peptide bond in the biuret test was taken to be 800 M-~; Draganid et al 1980). Apart from the peptidic material, two oligomers that are already formed at low doses and were considered earlier (Dragani6 et al 1980;Niketi6 1983;Niketi6 et al 1983) are among the radiolytic products contributing to the formation of the absorbing complex: oligoamide and urea-aldehyde.…”

“…5 shows that glycine is by far the most abundant amino acid. It originates not only from peptidic material, but also in the hydrolyses of certain carbamyl-glycine radiolytic products that are known to represent at least about 11% of the mass of dry residue: N-carbamylglycinonitrile (HCN, 6.4%; NH4CN, 3%), N-carbamylglycinamide (HCN, 3.1%;Niketi6 et al 1983), N-carbamylglycinoureid (HCN, 1.1%), and bis(carbamyl-glycyno)oxotriazine (NH4CN, 8.3%; Niketi6 1983). The rapid decrease in total amino acid concentration with increasing dose at doses up to about 40 Mrad is mainly due to loss of glycine from carbamyl-glycine derivatives.…”