The radiolysis and radioracemization of amino acids on silica surfaces

L-Leucine, deposited on both 1-quartz powder and on a commercial amorphous silica preparation (Syloid 63), has been subjected to irradiation in a⁶⁰Co -ray source, and the ensuing radiolysis and radioracemization have been determined gas chromatographically. The radiolysis and radioracemization observed for leucine on 1-quartz were rather similar to those noted for a crystalline L-leucine control. L-Leucine on Syloid 63, however, was vastly more susceptible to radiolysis as compared to the L-leucine control, and radioracemization was also markedly enhanced—each increasing with larger radiation dosage. L-Isovaline showed a similar, but diminished, enhancement of radiolysis sensitivity when adsorbed on the Syloid surface, but underwent no radioracemization whatsoever. The divergent results of the control and quartz-leucine irradiationsversus the Syloid-leucine and Syloid-isovaline irradiations are interpreted qualitatively in terms of the surface area parameters of the two silica adsorbents and the amino acid adsorbates.     

The radiolysis and radioracemization of amino acids on silica surfaces

L-Leucine, deposited on both 1-quartz powder and on a commercial amorphous silica preparation (Syloid 63), has been subjected to irradiation in a 60Co gamma-ray source, and the ensuing radiolysis and radioracemization have been determined gas chromatographically. The radiolysis and radioracemization observed for leucine on 1-quartz were rather similar to those noted for a crystalline L-leucine control. L-Leucine on Syloid 63, however, was vastly more susceptible to radiolysis as compared to the L-leucine control, and radioracemization was also markedly enhanced - each increasing with larger radiation dosage. L-Isovaline showed a similar, but diminished, enhancement of radiolysis sensitivity when adsorbed on the Syloid surface, but underwent no radioracemization whatsoever. The divergent results of the control and quartz-leucine irradiations versus the Syloid-leucine and Syloid-isovaline irradiations are interpreted qualitatively in terms of the surface area parameters of the two silica adsorbents and the amino acid adsorbates.     

The radiolysis and radioracemization of poly-L-leucines.

The brief history of the discovery of radioracemization, the racemization of an optically active substance induced by ionizing radiation, is reviewed. Our early studies involving the radiolysis and radioracemization of D- and L-leucine using gamma radiation from a 111-TBq 60Co gamma-ray source are described briefly, as are later experiments involving other protein amino acids and their salts, as well as the nonprotein amino acid, isovaline. The implications of the results of such studies for the Vester-Ulbricht mechanism which proposes longitudinally polarized beta radiation as the origin of molecular chirality, for the cosmological question of the enantiomeric compositions of amino acids in the Murchison meteorite, and for the use of D/L ratios of amino acids for geochronological and geothermal estimates are reviewed briefly. These past radiolysis-radio- racemization studies have involved only monomeric amino acids. The present research, extending such investigations to two homochiral L-leucine polypeptides, (L-Leu)10 and (L-Leu)78, was undertaken to see if a polymer of an amino acid might be more stable to radiolysis and radioracemization than the corresponding monomer. It was found that these polypeptides were more stable to radiolysis than was the leucine monomer, but that the extents of radioracemization in all samples were comparable.     

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.     

Chemiluminescence determination of hydroperoxides following radiolysis and photolysis of free amino acids

Hydroperoxides were determined in selected amino acids using three free radical generating systems by a sensitive (50 pmol limit of detection) and specific high performance liquid chromatography (HPLC)/chemiluminescence method. UVB and gamma radiation produced significant hydroperoxide formation, particularly in the aromatic amino acids tyrosine and tryptophan. Hydroperoxide yield was found to be dependent on both amino acid and irradiation source. Generation of hydrogen peroxide as a by-product of irradiation caused interference with chemiluminescence detection demonstrating the need for catalase addition. Hydroperoxides were not detectable following metal-catalysed H₂O₂ breakdown. We suggest that metal ions could interfere with the detection of hydroperoxides by causing preferential decomposition.     

The digital language of amino acids

Summary. The subject of this paper is a digital approach to the investigation of the biochemical basis of genetic processes. The digital mechanism of nucleic acid and protein bio-syntheses, the evolution of biomacromolecules and, especially, the biochemical evolution of genetic language have been analyzed by the application of cybernetic methods, information theory and system theory, respectively. This paper reports the discovery of new methods for developing the new technologies in genetics. It is about the most advanced digital technology which is based on program, cybernetics and informational systems and laws. The results in the practical application of the new technology could be useful in bioinformatics, genetics, biochemistry, medicine and other natural sciences.     

Effects of branched-chain amino acids on plasma amino acids in amyotrophic lateral sclerosis

Summary Although the cause of amyotrophic lateral sclerosis (ALS) remains unknown, biological findings suggest that the excitatory amino acid glutamate contributes to the pathogenesis of ALS. In previous studies of ALS, the therapeutic effect of the branched-chain amino acids (BCAAs) leucine, valine and isoleucine has been evaluated. The present study aimed at investigating the acute effect of BCAAs on plasma glutamate levels in ALS patients. Following two oral doses of BCAAs, significantly increased plasma levels were seen for valine (500%), isoleucine (1,377%) and leucine (927%), however the plasma level of glutamate was not affected. The plasma level of several other amino acids (tryptophan, tyrosine, phenylalanine and methionine) were found decreased after oral BCAAs, which may indicate a diminution in the rate of degradation of muscle protein and/or an increase in tissue disposal of amino acids.     

The reactions of the sulfur-containing amino acids with phosphoric and sulfuric acids

Both cystine and cysteine react very differently toward 6.0 M phosphoric and sulfuric acids. With phosphoric acid, extensive decomposi tion occurs; with sulfuric acid, very little.Cystine, in phosphoric acid at 100 °C. produces hydrogen sulfide, free sulfur, cysteic acid, ammonia, alanine, serine, and pyruvic acid. Cysteine produces a similar series but with marked quantitative differences.Cystine, in sulfuric acid, is merely racemized.Methionine is largely demethylated by sulfuric acid under these conditions. It is practically inert toward phosphoric acid.The behavior of hair toward phosphoric and sulfuric acids is similar to that of cystine but is modified by reactions of other hydrolytic products.     

The exchangeability of amino acids in proteins

The comparative analysis of protein sequences depends crucially on measures of amino acid similarity or distance. Many such measures exist, yet it is not known how well these measures reflect the operational exchangeability of amino acids in proteins, since most are derived by methods that confound a variety of effects, including effects of mutation. In pursuit of a pure measure of exchangeability, we present (1) a compilation of data on the effects of 9671 amino acid exchanges engineered and assayed in a set of 12 proteins; (2) a statistical procedure to combine results from diverse assays of exchange effects; (3) a matrix of "experimental exchangeability" values EX(ij) derived from applying this procedure to the compiled data; and (4) a set of three tests designed to evaluate the power of an exchangeability measure to (i) predict the effects of amino acid exchanges in the laboratory, (ii) account for the disease-causing potential of missense mutations in the human population, and (iii) model the probability of fixation of missense mutations in evolution. EX not only captures useful information on exchangeability while remaining free of other effects, but also outperforms all measures tested except for the best-performing alignment scoring matrix, which is comparable in performance.     

The conversion of amino acids in soils

Summary In an investigation on the conversion of amino acids in percolated soils, it was found that during the breakdown of glutamic acid to ammonia micro-organisms developed in the soil capable of denitrifying nitrite and nitrate to gaseous nitrogen. The enrichment of a soil with these micro-organisms was studied.Drying of the enriched soil had a deleterious effect on the activity of these micro-organisms.The interaction between denitrification and soil nitrification processes was studied in soil subjected to various percolation treatments. When the denitrifying micro-organisms and their metabolites were present in the soil the amount of nitrogen lost by denitrification depended on the availability of nitrite and nitrate. When this was supplied externally, in glutamate—nitrite or glutamate—nitrate mixtures, considerable reduction occurred. Losses were less severe where nitrite and nitrate entered the system internall y by nitrification of the ammonia produced from the breakdown of the amino acid. In fresh soils there were indications that the amount of nitrification occurring during amino-acid breakdown was the important factor.All the data appeared to be consistent with the hypothesis that during the conversion of amino acids in soils a delicate balance is established between nitrification and denitrification reactions by different types of soil micro-organisms.     

Administration of branched-chain amino acids during sustained exercise--effects on performance and on plasma concentration of some amino acids.

Previous studies have shown that sustained exercise in human subjects causes an increase in the plasma concentration ratio of free tryptophan: other large neutral amino acids [including the branched-chain amino acids (BCAA)]. This should favour the transport of tryptophan into the brain and also the synthesis of 5-hydroxytryptamine, which is thought to contribute to fatigue during prolonged exercise. A mixture of the three BCAA was given to subjects during a 30-km cross-country race or a marathon (42.2 km) and the effects on mental and physical performances were measured. The mental performance, measured as the performance in the Stroop Colour and Word Test (CWT), was improved after, as compared to before the 30-km cross-country race when a BCAA supplement was given during the race, whereas the CWT scores were similar before and after in the placebo group. The running performance in the marathon was improved for the "slower" runners (3.05 h-3.30 h) when BCAA was taken during the race; however, there was no significant effect on the performance in the "faster" runners (less than 3.05 h). The results showed that both mental and physical performance was improved by an intake of BCAA during exercise. In addition, the effects of exercise on the plasma concentration of the aromatic amino acids were altered when a BCAA supplement was given during the marathon.     

Transformation of some hydroxy amino acids to other amino acids.

It has been observed that beta-hydroxy-alpha-amino acids are transformed into other amino acids, when heated in dilute solutions with phosphorous acid, phosphoric acid or their ammonium salts. It has been shown that as in the case of previously reported glycine-aldehyde reactions, glycine also reacts with acetone to give beta-hydroxyvaline under prebiologically feasible conditions. It is suggested, therefore, that the formation of beta-hydroxy-alpha-amino acids and their transformation to other amino acids may have been a pathway for the synthesis of amino acids under primitive earth conditions.