Amino Acid Destruction Research Articles

Radiolytic Effects on Biological and Abiotic Amino Acids in Shallow Subsurface Ices on Europa and Enceladus.

Europa and Enceladus are key targets to search for evidence of life in our solar system. However, the surface and shallow subsurface of both airless icy moons are constantly bombarded by ionizing radiation that could degrade chemical biosignatures. Therefore, sampling of icy surfaces in future life detection missions to Europa and Enceladus requires a clear understanding of the necessary ice depth where unaltered organic biomolecules might be present. We conducted radiolysis experiments by exposing individual amino acids in ices and amino acids from dead microorganisms in ices to gamma radiation to simulate conditions on these icy worlds. In the pure amino acid samples, glycine did not show a detectable decrease in abundance, whereas the abundance of isovaline decreased by 40% after 4 MGy of exposure. Amino acids in dead Escherichia coli (E. coli) organic matter exhibited a gradual decline in abundances with the increase of exposure dosage, although at much slower rates than individual amino acids. The majority of amino acids in dead A. woodii samples demonstrated a step function decline as opposed to a gradual decline. After the initial drop in abundance with 1 MGy of exposure, those amino acids did not display further decreases in abundance after exposure up to 4 MGy. New radiolysis constants for isolated amino acids and amino acids in dead E. coli material for Europa/Enceladus-like conditions have been derived. Slow rates of amino acid destruction in biological samples under Europa and Enceladus-like surface conditions bolster the case for future life detection measurements by Europa and Enceladus lander missions. Based on our measurements, the "safe" sampling depth on Europa is ∼20 cm at high latitudes of the trailing hemisphere in the area of little impact gardening. Subsurface sampling is not required for the detection of amino acids on Enceladus-these molecules will survive radiolysis at any location on the Enceladus surface. If the stability of amino acids observed in A. woodii organic materials is confirmed in other microorganisms, then the survival of amino acids from a potential biosphere in Europa ice would be significantly increased.

Rapid Radiolytic Degradation of Amino Acids in the Martian Shallow Subsurface: Implications for the Search for Extinct Life.

Amino acids are fundamental to life as we know them as the monomers of proteins and enzymes. They are also readily synthesized under a variety of plausible prebiotic conditions and are common in carbon-rich meteorites. Thus, they represent a reasonable class of organics to target in the search for prebiotic chemistry or chemical evidence of life on Mars. However, regardless of their origin, amino acids and other organic molecules present in near-surface regolith and rocks on Mars can be degraded by exposure to cosmic rays that can penetrate to a depth of a few meters. We exposed several pure amino acids in dry and hydrated silicate mixtures and in mixtures of silicates with perchlorate salts to gamma radiation at various temperatures and radiation doses representative of the martian near-subsurface. We found that irradiation of amino acids mixed with dry silica powder increased the rate of amino acid radiolysis, with the radiolysis constants of amino acids in silicate mixtures at least a factor of 10 larger compared with the radiolysis constants of amino acids alone. The addition of perchlorate salts to the silicate samples or hydration of silicate samples further accelerated the rate of amino acid destruction during irradiation and increased the radiolysis constants by a factor of ∼1.5. Our results suggest that even low-molecular-weight amino acids could degrade in just ∼20 million years in the top 10 cm of the martian surface regolith and rock, and even faster if the material contains elevated abundances of hydrated silicate minerals or perchlorates. We did not detect evidence of amino acid racemization after gamma radiation exposure of the samples, which indicates that the chirality of some surviving amino acids may still be preserved. Our experimental results suggest serious challenges for the search of ancient amino acids and other potential organic biosignatures in the top 2 m of the martian surface.

Possible survival of simple amino acids to X-ray irradiation in ice: the case of glycine

Context. Glycine, the simplest of amino acids, has been found in several carbonaceous meteorites collected on Earth, though its presence in the interstellar medium (ISM) has never been confirmed as of today. It is now considered that its synthesis took place in the icy mantles of interstellar grains, but it remains unclear how glycine, once synthesized and trapped in interplanetary particles, survives during the transfer to the Earth.Aims. Assuming that glycine was effectively formed in the ice, we address the question of its resistance to a solar-like radiation field and look for the possible molecular remnants that would be useful tracers of its former existence.Methods. The search was conducted using an interdisciplinary approach that mixes, on the one hand, irradiations in ultra high vacuum at 30 K on the TEMPO beam line of the synchrotron SOLEIL, simultaneously with near-edge X-ray absorption spectroscopy (NEXAFS) measurements, and on the other hand, quantum calculations to determine the energetics of the fragmentations and the relative stability of the different byproducts. The last points were addressed by means of density functional theory (DFT) simulations followed by high-level post Hartree-Fock calculations when more accurate relative energies were necessary. The constraints of an icy environment deserved special attention and the ice was modeled by a polarizable continuum medium that relies on the dielectric constant of water ice at 10–50 K.Results. Destruction of glycine is observed in the first seconds of irradiation, and carbon dioxide (CO2 ) and methylamine (CH3 NH2 ) are formed. Carbon monoxide (CO), methanimine (CH2 NH) and hydrogen cyanide (HCN) are also produced in secondary reactions. The amino acid destruction is the same for pure glycine and glycine in ice, indicating that the OH radicals released by the water matrix is barely involved in the photolytic process; however, these radicals are involved in the production of the secondary byproducts through dehydrogenation reactions as shown by ab initio quantum chemical simulation presented in this article along with the experimental results.Conclusions. The experiments show that glycine is only partially destroyed. Its abundance is found to stay at a level of ~30% of the initial concentration, for an irradiation dose equivalent to three years of solar radiation (at a distance of one astronomical unit). This result supports the hypothesis that, if trapped in protected icy environments and/or in the interior of interplanetary particles and meteorites, glycine may partly resist the radiation field to which it is submitted and, accordingly, survives its journey to the Earth.

Modification of amino acids at shock pressures of 3.5 to 32 GPa

Amino acids were subjected to shock impact over a pressure range of 3.5 to 32 GPa both within and without meteoritic mineral matrices. The extent of amino acid destruction, racemization, and conversion to secondary amino acids was examined. Abundances of parent compounds decreased by a factor of 10 3 over this pressure range. Racemization also occurred, but some residual optical activity remained in the amino acids surviving shocks up to 32 GPa. Secondary amino acids formed in the high peak pressure range; those identified were β-alanine, glycine, alanine, γ-aminobutyric acid, and β-aminoisobutyric acid. At 30 GPa, the abundances of these daughter compounds exceeded those of the remaining initial amino acids. As the concomitant effects of high mechanical stress and temperature accompanying shocks cannot be separated in this work, their relative contribution to the observed transformations cannot be estimated. The survival of amino acids in shock experiments suggests that, after formation or emplacement of amino acids in carbonaceous chondrite parent bodies, these objects never experienced impact velocities greater than 5 km/s, which suffices to generate 30 GPa for typical silicate/silicate impacts. These results also provide guidelines for choosing appropriate capture media for interplanetary dust particles on Earth-orbiting platforms.

Effect of Extrusion on Feed Characteristics and Broiler Chicken Performance

Broiler feeds of identical formulas were fed to straight run broilers in the form of either non-heat treated mash, pellets, or extruded pellets to test the effect of feed processing on production parameters. Young broilers at ≤ 2wk old which were fed crumbled starter rations extruded prior to crumbling weighed more than birds fed crumbled starter rations that were pelleted prior to crumbling. However, when broilers received rations not crumbled following processing, birds fed extruded diets weighed less than those fed pelleted diets. Extruded feeds weighed less per unit volume than pelleted feeds. This density difference may account for the differences in body weights observed. The traditional ether extraction procedure detected a smaller percentage of the fat present in extruded feeds than did acid hydrolysis procedures. In addition, the extrusion process caused some protein and amino acid destruction. Therefore, extruded rations should be formulated at slightly higher nutrient density to compensate for nutrient destruction and loss of nutrient digestibility.

The hydrolysis of proteins by microwave energy

Microwave energy, at manually-adjusted, partial power settings has been used to hydrolyse bovine serum albumin at 125 °C. Hydrolysis was complete within 2 h, except for valine and isoleucine which were completely liberated within 4 h. The aminoacid destruction was less than that observed at similar hydrolysis conditions with other methods and complete hydrolysis was achieved more rapidly. These results provide a basis for automating the process of amino-acid hydrolysis.

Effect of γ Irradiation on the α and β Chains of Bovine Hemoglobin and Globin

Hemoglobin was obtained from the blood of lowland black and white cattle with HbA phenotype by the method of Drabkin. Water solutions of hemoglobin (Hb) or globin (Gl) in 20 mM KH2 PO4 were γ-irradiated with a dose of 2 Mrad, and the amino acid composition of α and β chains of control and irradiated Hb and Gl, separated according to Clegg et al., was analyzed. Quantitative differences were found between the radiation sensitivities of α and β chains of Hb and Gl; Gl chains (heme free) were more susceptible to the obtained results. A sequence of radiation sensitivity of individual amino acids in α and β chains of Hb and Gl was determined. In the β chains, amino acid destruction was considerably higher than in α chains. These changes were confirmed by amino acid analysis which showed that Cys, Met, Tyr, Arg, Ser, Thr, Pro, and His residues were most destroyed or modified following irradiation.

Radiation damage of proteins in the solid state: Changes of amino acid composition in catalase

Catalase has been irradiated with 100 keV electrons under conditions simulating the hazards of electron microscopic imaging. Amino acid analysis reveals a definite pattern of amino acid destruction which is well correlated with the particular chemical structures of amino acid side chains. This pattern appears to be distinctly different from the sensitivity pattern for monoamino acid systems, which fact is ascribed to intramolecular energy transfer and selective attack of liberated radicals.

Effect of the Volume of HCl in Minimizing Amino Acid Losses when Carbohydrate-Containing Samples Are Hydrolyzed

Investigations were conducted to determine the optimum level of hydrochloric acid required to minimize amino acid destruction during hydrolysis with samples containing carbohydrate. With the exception of serine, recoveries for all of the amino acids from hydrolysates containing the (HCl to Glucose) ratio of 2851:1 were not lowered more than 3.2% when compared with the hydrolyzed standard mixture. When the (HCl to Glucose) ratio was lowered from 2851:1 to 712:1, the following statistically significant percent losses to basic and hydroxyl amino acids occurred: histidine 1.2, lysine 2.8, serine 6.0 and threonine 6.8. With corn hydrolysates, the basic-hydroxyl amino acid degradative trend continued as the calculated (HCl to Carbohydrate) ratio of 712:1 was lowered to 260:1. The statistically significant percent losses which occurred were as follows: arginine 4.5, serine 4.3, methionine 9.8 and glycine 5.5. With the types of carbohydrate investigated, the results indicate that a reasonable milligram (HCl to Carbohydrate) ratio for minimizing amino acid destruction during hydrolysis be greater than 700:1 and preferably 2800:1. The ratios used in both studies are of practical importance, since they span carbohydrate: amino acid ratios which exist in various feedstuffs and mixed diets.

The Photolysis of Tyrosine and its Possible Relationship to the Yellowing of Wool

Tyrosine, in the presence of air is degraded by uv light to 3,4-dihydroxyphenylalanine (DOPA), ammonia and a yellow-brown pigment. The rate of production of the pigment, as measured by the Yellowness Index (YI), is very pH-dependent, production being most rapid in alkaline solution. The degradation of tyrosine is less pH-dependent. When the tyrosine was totally degraded, the pigment could be bleached by further exposure to the irradiation. In an atmosphere of nitrogen, degradation of tyrosine is slower and no pigment is formed. Thus, decomposition may proceed through either of two alternative mechanisms. In that mechanism in which pigment is produced, bleaching simultaneously occurs, but at a slower rate than color production. It is concluded that there is not necessarily a quantitative relationship between amino acid destruction and pigment producion.

Zur Strahleninaktivierung von Ribonuclease

Dry ribonuclease was irradiated with 60Co gamma radiation in vacuo, under oxygen atmosphere, and at 77 °K. By chromatography on Sephadex G-50 active ribonuclease was separated from inactive radiation products. From the elution pattern and by ultracentrifugation it was shown that mainly unfolded dimers are formed by gamma irradiation of dry ribonuclease. Amino acid analysis of these various products shows that in all components cystine, methionine, tyrosine, phenylalanine, lysine, and histidine are destroyed with increasing dose whereas glycine shows a small increase. Thus, in ribonuclease irradiated in the dry state the same amino acids are changed as was found after irradiation in aqueous solutions. The radiosensitivity of dry ribonuclease shows an increase by the presence of oxygen of about 2 and a decrease at low temperature in vacuo of about 5. The same factors were also found for the alteration of amino acids, which means that under various experimental conditions amino acid destruction is proportional to loss of enzymatic activity of ribonuclease. The observed selectivity of amino acid destruction may be explained by energy migration or by the attack of atomic hydrogen liberated at random from the molecule. The total number of amino acids destroyed per ribonuclease molecule increases with dose. In enzymatically inactive products this value is always higher by one amino acid residue than in the active components. From this result and from the increase with dose it is concluded that after destruction of one amino acid residue the ribonuclease molecule has a probability (not depending on dose of irradiation) of 0.45 to become inactivated whereas in 55 per cent of all cases the molecule maintains its enzymatic activity.

Irradiation of deoxyribonucleohistone solutions I. Amino acid destruction

1. 1. 60Co-γ-irradiation of deoxynucleohistone and of histone solutions has been carried out in order to determine the nature and the extent of amino acid destruction. 2. 2. The results show that amino acids are attacked, in both cases, to an extent depending upon their reactivity towards hydroxyl radicals and upon their relative concentration in the histone. 3. 3. Comparison of the total attack on deoxynucleohistone and on histone shows these to be approximately equal, thus confirming previous suggestions that the DNA in deoxynucleohistone is protected to a large extent from attack by the radiation-produced active species.

Damage to proteins, enzymes, and amino acids by peroxidizing lipids

Transient free-radicals are produced in peroxidizing lipid-protein reaction systems. The pattern of damage to proteins, induced by these radicals, is similar to that observed in the case of radiation damage; proteins and enzymes lose solubility and constituent amino acids are destroyed. Lipid peroxidation damage appears to be about one-tenth as effective as radiation damage. Amino acid destruction was measured in lipid-peroxidation damaged γ-globulin, catalase, serum albumin, hemoglobin, and and ovalbumin. Among the most labile amino acids are methionine, histidine, cystine, and lysine. Major products of lipid peroxidation-cysteine interaction are hydrogen sulfide and cystine.

Effects of Gamma Radiation on Ribonuclease

dose is high enough, it is necessary to determine which of the three is predominant at a lower dose. According to Platzman and Franck (1), a number of hydrogen bonds will be temporarily severed in the vicinity of an ionization because the sudden introduction of a charge disrupts electrical dipoles and thus induces a rearrangement of polar groups in the vicinity of the charge. This rearrangement could rupture several hydrogen bonds, thereby destroying the secondary structure of the molecule. In order to evaluate the effect of radiation on hydrogen bonding in proteins, we employed infrared spectral analysis at 1550 cm-1 of the time-dependent decrease in the intensity for the protein in D20 (2). Chemical determination of amino acid destruction was used to gain information about covalent changes. The results obtained by these two types of studies have been correlated with the loss in enzymatic activity and are reported here.