Evidence of amino acids in hydrolysates of compounds formed by ionizing radiations

It has been shown that the action of ionizing radiations on dilute, oxygen-free, aqueous solutions of acetonitrile and propionitrile leads to the formation of oligomers, which upon hydrolyses release amino acids. The presence of nine amino acids, the same as those found in irradiated aqueous cyanides, has been established. Those amino acids with asymmetric carbon atoms separated by GC method, appeared to consist of nearly equal amounts of D and L isomers. Glycine is the most abundant amino acid in hydrolysates of acetonitrile, while alanine appears in the samples of propionitrile. A comparison of all amino acids, identified in hydrolysates of various cyanides and nitriles, suggests that it is the cyano group, and a free-radical initiated mechanism, that is primarily involved in these radiation-chemical changes of potential interest to prebiotic chemistry.     

Evidence for amino acids in hydrolysates of compounds formed by ionizing radiations

Dilute, O₂-free aqueous cyanides were exposed to multikilorad doses of a radioactive cobalt source. After the removal of unreacted cyanides and of volatile radiolytic products, the residue was ydrolyzed and the resulting material analyzed for amino acids. The results show the presence of five protein amino acids and five amino acids which do not occur in natural proteins. The amino acids of enantiomeric derivatives separated on an optically active column, appeared to consist of approximately equal amounts of D and L isomers. Radiation-chemical yields of amino acids were determined at various radiation doses. The results obtained support the previous findings that the free-radical initiated process is the source of oligomers which on hydrolysis release the amino acids.     

Studies on C3 convertases. Inhibition of C5 convertase formation by peptides containing aromatic amino acids.

The influence of various peptides containing the aromatic amino acids phenylalanine and tyrosine on the formation of the enzyme EAC1423 of the complement system from component C3 and enzyme EAC142 was investigated. Kinetic analysis of enzyme EAC1423 formation and studies on the binding of the C3b fragment of 125I-labelled component C3 to enzyme EAC142 both showed that binding of the C3b fragment of component C3 was decreased by the peptides. Kinetic studies on component-C3 turnover in the fluid phase of enzyme EAC142 failed to reveal effects of the peptides. However, an initial lag in component-C3 turnover occurred that at constant component-C3 concentration was inversely proportional to enzyme EAC142 concentration. This lag in enzyme EAC142 activity is considered as an indication that the interaction of enzyme EAC142 with component C3 possibly does not follow simple Michaelis-Menten kinetics, as was previously assumed. It is shown that the stages after enzyme EAC1423 formation are not influenced by the peptides, suggesting a high degree of specificity of the peptides for the inhibition of enzyme EAC1423 formation.     

Regio and stereoselective oxidations of unsaturated steroidal compounds with H2O2 mediated by CH3ReO3

We have investigated the oxidative behavior of sterols such as cholesteryl acetate (1), 7-dehydrocholesteryl acetate (2), ergosteryl acetate (3), cholecalciferol acetate (Vitamin D(3) acetate) (4) and ergocalciferol acetate (Vitamin D(2) acetate) (5) with the oxidant system methyltrioxorhenium/H(2)O(2)/pyridine in order to check potential parameters controlling the selectivity. The reactions, performed in CH(2)Cl(2)/H(2)O at 25 degrees C, have shown good regio- and stereoselectivity. All oxidation products were isolated by high-performance liquid chromatography (HPLC) and characterized by MS(EI) or FAB, (1)H NMR, (13)C NMR, APT, COSY, HSQC, HMBC, ROESY and NOEDS measurements. Seven new oxygenated compounds were also obtained. Under the experimental conditions adopted in this work, only the diene steroids, i.e. 7-dehydrocholesteryl acetate and ergosteryl acetate, undergo hydrolytic oxirane ring opening, whereas Vitamin D(2) and D(3) acetates, containing the triene system and cholesteryl acetate yield only epoxides. The selectivity seems to be controlled by the nucleophilicity of double bonds and by stereoelectronic and steric effects.     

Aqueous solutions containing amino acids and peptides. Part 20. Volumetric behavior of some terminally substituted amino acids and peptides at 298.15 K

The densities at 298.15 K of aqueous solutions containing some terminally substituted amino acids and peptides containing the glycyl, L -and D -alanyl, L -leucyl, sarcosyl, and L -prolyl residues have been dertermined and standard state partial molar volumes and volumetric pairwise virial coefficients obtained. It is shown that the partial molar volumes can be represented using group volume contributions, but this approach is only approximate, and significant effects of N-terminal substitution and sequence dependence are observed. The volumetric virial coefficients for the amino acid amides have been expressed using a group-additivity approach, and the results obtained indicate that the dominant contributions come from peptide group interactions with other peptide groups and with hydrophobic groups. There is also some evidence of both sequence and chiral effects on the volumetric virial coefficients for proline-containing dipeptides.     

A comparison of the effects of ultraviolet and ionizing radiations on trypsin activity and on its constituent amino acids

Photons of 254nm. u.v. light, (60)Co gamma-rays and 1Mev electrons produce different patterns of destruction of individual amino acids in dried films of trypsin and in the corresponding amino acid mixture. For example, in the amino acid mixture u.v. light destroys tyrosine, tryptophan and cystine, whereas in trypsin only cystine is disrupted but with 10 times the initial yield. Further, in the amino acid mixture loss of half-cystine is a simple exponential function of dose, but in trypsin there appear to be two exponential components of the loss with yields that differ by a factor of 35. Both the gamma-rays and electrons destroy half-cystine, tryptophan, histidine and methionine in the amino acid mixture with remarkably high yields, whereas in trypsin doses that destroy almost all of the enzymic activity produce no detectable destruction of amino acid residues. These marked differences between the two preparations show that the radiation-sensitivity of a given amino acid alone and in a protein is different, and suggests that in trypsin there is fairly extensive migration of energy, charge or both with localization of damage at specific sites determined by this enzyme's internal organization. All three types of radiation produce appreciable amounts of ;damaged' (not completely inactivated) molecules which are prevented from reassuming an active configuration by the addition of 5.5m-urea; thiol reagents have a similar effect after bombardment with u.v. light or electrons. The patterns of destruction produced by gamma-rays and by electrons in both the amino acid mixture and in trypsin are different (some of the yields vary by a factor of 30). This result appears to be inconsistent with the popular belief that most of the energy absorbed from gamma-rays is associated with very-high-energy electrons.     

Gustatory responses to amino acids in the chorda tympani nerve of C3H mice

Integrated neural responses to various amino acids were recorded from thechorda tympani (facial) nerve in C3H mice. The basic amino acidshydrochlorides L-Arg-HCl and L-Lys-HCl evoked large magnitude integratedtaste responses, similar to that for NaCl, and had estimatedelectrophysiological thresholds of 0.0001 M. No significant difference wasindicated between the response magnitudes for the L- and D-forms of thebasic amino acid hydrochlorides; however, responses to the basic amino acidhydrochlorides cross-adapted with NaCl. Responses to neutral L-amino acids(Ser, Ala, Gly), which taste sweet to humans, showed higher thresholds(>0.0003 M), similar to that for sucrose, and did not cross-adapt withbasic amino acid hydrochlorides or with NaCl. Responses to the neutralamino acids L-Ser and L-Ala were larger than those to their D-amino acidenantiomers. The acidic amino acids L-Asp and L-Glu showedconcentration-response functions different from that for HCl. Both acidicamino acids were more stimulatory than HCl at the same pH, although theresponses to them were cross-adapted by HCl, indicating a pH effect. Acomparison of the stimulatory effectiveness among amino acid derivativesand analogues suggested that the alpha- amino group is essential for thestimulatory effectiveness of neutral amino acids.     

The effect of 2-oxoglutarate and biotin in the release of amino acids by Citrobacter intermedius C3

Excretion of amino acids by Citrobacter intermedius C3 was assayed in a mineral medium with glucose as carbon source. Glutamic acid is the main amino acid excreted in liquid medium and it is also detected at the colonial level in solid medium. Mutants with different behaviour with respect to the excretion of amino acids are studied. The presence of 2-oxoglutarate in the medium induced excretion in all strains. On the other hand when biotin was added to the culture media amino acid excretion was partially reduced.     

Formation of prebiochemical compounds in models of the primitive earth's atmosphere. II: CH4 - H2S atmospheres.

In order to understand the role of sulfur in the primitive atmosphere, we have studied the action of a silent discharge on mixtures of CH4 and H2S at low pressure. The nature of the products formed in the gaseous phase, and the influence of several parameters, especially the H2S percentage, on the yield of the products are reported. The analysis of the products is carried out by gas liquid chromatography and infrared spectrometry. The formation of sulfur-containing compounds, such as thiols and sulfides, is reported. CS2 is formed in high yield (a few percent) in mixtures containing 40-50% of H2S, while the maximum concentration of thiols (i.e., CH3SH and C2H5SH) is reached with lower percentages of H2S. The formation of hydrocarbons decreases rapidly with increasing proportions of H2S. These results show the important inhibitor effect of H2S on the formation of hydrocarbons and the possibility of occurrence of many sulfur compounds in prebiological evolution.     

The radioracemization of amino acids by ionizing radiation: Geochemical and cosmochemical implications

A number of optically active amino acids, both in the solid state and as sodium or hydrochloride salts in aqueous solution, have been exposed to ionizing radiation from a 3000 Ci⁶⁰Co -ray source to see if radioracemization might accompany their well-known radiolysis. -Ray doses causing 55–68% radiolysis of solid amino acids typically engendered 2–5% racemization, while aqueous solutions of the sodium salts of amino acids which underwent 53–66% radiolysis showed 5–11% racemization. Amino acid hydrochloride salts in aqueous solution, on the other hand, showed little or no radioracemization accompanying their radiolysis. Both radiolysis, and radioracemization were roughly proportional to -ray dose in the range studied (1–36×10⁶ rads). Mechanisms for the radioracemization of amino acids in the solid state and as aqueous sodium salts are discussed, and the absence of radioracemization for aqueous hydrochloride salts is rationalized. Isovaline, a non-protein amino acid which has been isolated from the Murchison meteorite, contains no -hydrogen atom and is therefore incapable of racemizationvia the chemical mechanisms by which ordinary amino acids racemize. Nevertheless, isovaline suffers radioracemization in the solid state to an extent comparable to that shown by ordinary amino acids, as do its sodium and hydrochloride salts in the solid state. The sodium salt of isovaline in aqueous solution, however, fails to racemize during its radiolysis. Several implicaitons of the newly described phenomenon of radiomization are pointed out for the fields of geochemistry and cosmochemistry.A portion of this research has been described previously at the 144th National Meeting of the American Association for the Advancement of Science, Washington D.C., Feb. 12–17, 1978, at the Fourth College Park Colloquium on Chemical Evolution, University of Maryland, College Park, Maryland, Oct. 18–20, 1978, and at the Carnegie Institution of Washington Conference: Advances in the Biogeochemistry of Amino Acids, Airlie House, Warrenton, Virginia, Oct. 29—Nov. 1, 1978.