Direct interaction between amino acids and nucleotides as a possible physicochemical basis for the origin of the genetic code.

A study of the association of homocodonic amino acids and selected heterocodonic amino acids with selected nucleotides in aqueous solution was undertaken to examine a possible physical basis for the origin of codon assignments. These interactions were studied using 1H nuclear magnetic resonance spectroscopy (NMR). Association constants for the various interactions were determined by fitting the changes in the chemical shifts of the anomeric and ring protons of the nucleoside moieties as a function of amino acid concentration to an isotherm which described the binding interaction. The strongest association of all homocodonic amino acids were with their respective anticodonic nucleotide sequences. The strength of association was seen to increase with increase in the chain length of the anticodonic nucleotide. The association of these amino acids with different phosphate esters of nucleotides suggests that a definite isomeric structure is required for association with a specified amino acid; the 5'-mononucleotides and (3'-5')-linked dinucleotides are the favored geometries for strong associations. Use of heterocodonic amino acids and nonprotein amino acids supports these findings. We conclude that there is at least a physicochemical, anticodonic contribution to the origin of the genetic code.     

Amino acids in meteorites.

Carbonaceous chondrites carry a record of chemical evolution that is unparalleled among presently accessible natural materials. Within the complex suite of organic compounds that characterize these meteorites, amino acids occur at a total concentration that may reach 0.6 micromole g-1 meteorite (approximately 60 ppm). Both free amino acids and acid-labile amino acid derivatives have been found in hot-water extracts of a CI1 and seven CM2 chondrites. Although the amino acid composition of all CM2 chondrites is not the same, differences may be largely explicable on the basis of spontaneous and biologically-caused decomposition occurring during their terrestrial residence. The amino acids of the Murchison meteorite (CM2) have been extensively analyzed and 52 amino acids have been positively identified. Thirty three of these amino acids are unknown in natural materials other than carbonaceous chondrites. Thus the Murchison meteorite has recently been the major source of new naturally-occurring amino acids. The Murchison amino acids comprise a mixture of C2 through C8 cyclic and acyclic monoamino alkanoic and alkandioic acids of nearly complete structural diversity. Within the acyclic monoamino alkanoic acid series, primary alpha-amino alpha-branched amino acids are predominant. The concentrations of individual amino acids decline exponentially with increasing carbon number within homologous series. Amino acid enantiomers are found in approximately equal amounts. Eight of the terrestrial protein amino acids have been found.     

Stable isotope analysis at the molecular level: a new approach for determining the origins of amino acids in the Murchison meteorite.

A combined gas chromatography/isotope ratio mass spectrometry (GC/IRMS) method has been developed that permits the direct stable carbon isotope analysis of N(O)-trifluoroacetyl-isopropyl esters of individual amino acids and their respective enantiomers at nanomole abundances. Calculation of the original delta 13C values of the amino acids is accomplished via a correction for the carbon introduced during the derivatization process. Previous GC/IRMS analyses of individual amino acids in the non-hydrolyzed water extract of an interior sample of a Murchison meteorite stone revealed an enrichment in 13C relative to terrestrial organic matter, in agreement with previous findings for bulk extracts. The range of amino acid delta 13C values (+5 to +30%, PDB) suggests possible kinetic effects during synthesis. In this study, an apparent kinetic isotope effect was also observed for the amino acid products of a spark discharge experiment. These preliminary results are supportive of a similar mechanism for the abiotic synthesis of amino acids in the Murchison meteorite.     

Extinction of dinosaurs: a possible novel cause.

A novel cause of mass extinction of fauna close to the (K/T) Boundary is suggested. A large amount of non-protein amino acids (AIB and ISOVAL) has been observed close to this event. It is speculated that these amino acids may be toxic and are responsible for the extinction. The toxicity level is estimated for this suggestion to be true and experimentalists are encouraged to test this level of toxicity for the amino acids.     

Formation of amino acid precursors in cometary ice environments by cosmic radiation.

Cometary ices are believed to contain water, carbon monoxide, methane and ammonia, and are possible sites for the formation and preservation of organic compounds relating to the origin of life. Cosmic rays, together with ultraviolet light, are among the most effective energy sources for the formation of organic compounds in space. In order to study the possibility of the formation of amino acids in comets or their precursory bodies (interstellar dust grains), several types of ice mixtures made in a cryostat at 10 K ("simulated cometary ices") were irradiated with high energy protons. After irradiation, the volatile products were analyzed with a quadrupole mass spectrometer, while temperature of the cryostat was raised to room temperature. The non-volatile products remaining in the cryostat at room temperature were collected with water. They were acid-hydrolyzed, and analyzed by ion-exchange chromatography. When an ice mixture of carbon monoxide (or methane), ammonia and water was irradiated, some hydrocarbons were formed, and amino acids such as glycine and alanine were detected in the hydrolyzate. These results suggest the possible formation of "amino acid precursors" (compounds yielding amino acids after hydrolysis) in interstellar dust grains by cosmic radiation. We previously reported that amino acid precursors were formed when simulated primitive planetary atmospheres were irradiated with cosmic ray particles. It will be of great interest to compare the amount of bioorganic compounds that were formed in the primitive earth and that brought by comets to the earth.     

Detection of martian amino acids by chemical derivatization coupled to gas chromatography: in situ and laboratory analysis.

If there is, or ever was, life in our solar system beyond the Earth, Mars is the most likely place to search for. Future space missions will have then to take into account the detection of prebiotic molecules or molecules of biological significance such as amino acids. Techniques of analysis used for returned samples have to be very sensitive and avoid any chemical or biological contamination whereas in situ techniques have to be automated, fast and low energy consuming. Several possible methods could be used for in situ amino acid analyses on Mars, but gas chromatography would likely be the most suitable. Returned samples could be analyzed by any method in routine laboratory use such as gas chromatography, already successfully performed for analyses of organic matter including amino acids from martian meteorites. The derivatization step, which volatilizes amino acids to perform both in situ and laboratory analysis by gas chromatography, is discussed here.     

The atmosphere of the primitive earth and the prebiotic synthesis of organic compounds.

The prebiotic synthesis of organic compounds using a spark discharge on various simulated prebiotic atmospheres at 25 degrees has been studied. Methane mixtures contained H2 + CH4 + H2O + N2 + NH3 with H2/CH4 molar ratios from 0 to 4 and pNH3 = 0.1 torr. A similar set of experiments without added NH3 was performed. The yields of amino acids (1.2 to 4.7% based on the carbon) are approximately independent of the H2/CH4 ratio and the presence of added NH3, and a wide variety of amino acids are obtained. Mixtures of H2 + CO + H2O + N2 and H2 + CO2 + H2O + N2, with and without added NH3, all give about 2% yields of amino acids at H2/CO and H2/CO2 ratios of 2 to 4. For the H2/CO and H2/CO2 ratios less than 1, the yields fall off drastically to as low as 10(-3)%. Glycine is almost the only amino acid produced from CO and CO2 atmospheres. These results show that the maximum yield is about the same for the three carbon sources at high H2/carbon ratios, but that CH4 is superior at low H2/carbon ratios. In addition, CH4 gives a much greater variety of amino acids than either CO or CO2. If it is assumed that amino acids more complex than glycine were required for the origin of life, then these results indicate the need for CH4 in the primitive atmosphere. The yields of cyanide and formaldehyde parallel the amino acid results, with yields of HCN and H2CO as high as 13% based on the carbon. Ammonia is also produced from N2 in experiments with no added NH3 in yields as high as 4.9%. These results show that large amounts of NH3 would have been synthesized on the primitive earth by electric discharges. The amount of ammonia formed by hydrolysis of HCN and various nitriles may have exceeded that formed directly in electric discharges.     

Formation of bioorganic compounds in planetary atmospheres by cosmic radiation.

Simulated planetary atmospheres (mixtures of simple gases) were irradiated with high energy particles to simulate an action of cosmic rays. When a mixture of carbon monoxide, nitrogen and water was irradiated with 2.8-40 MeV protons, a wide variety of bioorganic compounds including amino acids, imidazole, and uracil were identified in the products. The amount of amino acids was proportional to the energy deposit to the system. Various kinds of simulated planetary atmospheres, such as "Titan type" and "Jovian type", were also irradiated with high energy protons, and gave amino acids in the hydrolyzed products. Since cosmic rays are a universal energy source in space, it was suggested that formation of bioorganic compounds in planetary atmospheres is inevitable in the course of cosmic evolution.     

Survivability of biomolecules during extraterrestrial delivery: new results on pyrolysis of amino acids and poly-amino acids.

The hypothesis on exogenous origin of organic matter on the early Earth is strongly supported by the detection of a large variety of organic compounds (including amino acids and nucleobases) in carbonaceous chondrites. Whether such complex species can be successively delivered by other space bodies (comets, asteroids and interplanetary dust particles) is unclear and depends primarily on capability of the biomolecules to survive high temperatures during atmospheric deceleration and impacts to the terrestrial surface. Recent simulation experiments on amino acid and nucleic acid base pyrolysis under oxygen-free atmosphere demonstrated that simple representatives of these (considered thermally unstable) compounds can survive at 1-10% level a rapid heating at 500-600 degrees C. In the present work, we report on new data on the pyrolysis of amino acids and their homopolymers and discuss implications of their thermal behavior for extraterrestrial delivery.     

Some observations on amino acid racemization under pyrolytic temperatures and inorganic oxide-catalyzed intermolecular condensation.

The problem of homochirality is of crucial importance for the origins of Life. While most laboratory studies are focused on the search of physical and chemical sources of handedness in the Universe, they reflect only one aspect of the problem: the origin of homochiral biomolecules. At the same time, any space environments where biomolecules are expected to form and where they have to pass through before the first primitive forms of Life emerge, include strong irradiation or/and high temperatures. This automatically implies the possibility of losing the optical activity, i.e. racemization. The simulation experiments performed by our group deal with the following two aspects of amino acid abiotic chemistry: (1) amino acid pyrolysis associated with their extraterrestrial delivery; and (2) peptide formation from amino acids catalyzed by inorganic oxides. According to our observations, the racemization phenomena are very common in the systems considered, not only under pyrolytic temperatures, but in some cases also under rather mild conditions (<100 degrees C). Our results put additional constraints on the environments where the chirality of biomolecules can be efficiently preserved.     

Characteristics and formation of amino acids and hydroxy acids of the Murchison meteorite.

Eight characteristics of the unique suite of amino acids and hydroxy acids found in the Murchison meteorite can be recognized on the basis of detailed molecular and isotopic analyses. The marked structural correspondence between the alpha-amino acids and alpha-hydroxy acids and the high deuterium/hydrogen ratio argue persuasively for their formation by aqueous phase Strecker reactions in the meteorite parent body from presolar, i.e., interstellar, aldehydes, ketones, ammonia, and hydrogen cyanide. The characteristics of the meteoritic suite of amino acids and hydroxy acids are briefly enumerated and discussed with regard to their consonance with this interstellar-parent body formation hypothesis. The hypothesis has interesting implications for the organic composition of both the primitive parent body and the presolar nebula.     

Formation of oligopeptides on the surface of small bodies in solar system by cosmic radiation.

The present experiment indicates that oligopeptides are easily produced in solid state from mixtures of simple amino acids by irradiating with high energy charged particles. We investigated such amino acids and their mixtures as tryptophan, tyrosine and glycine. The thin films was irradiated with protons (6.6 MeV). Such dipeptides as Trp-Trp, Gly-Tyr, Tyr-Gly, and Tyr-Tyr have been detected as products of irradiation. Cosmic rays might be an effective energy source for abiotic formation of bioorganic compounds on the surface of small bodies in the solar system on early stage of formation of planets as well as at present day.     

Possible complex organic compounds on Mars.

It is suggested that primitive Mars had somehow similar environments as primitive Earth. If life was born on the primitive earth using organic compounds which were produced from the early Earth environment, the same types of organic compounds were also formed on primitive Mars. Such organic compounds might have been preserved on Mars still now. We are studying possible organic formation on primitive and present Mars. A gaseous mixture of CO2, CO, N2 and H2O with various mixing ratios were irradiated with high energy protons (major components of cosmic rays). Hydrogen cyanide and formaldehyde were detected among volatile products, and yellow-brown-colored water-soluble non-volatile substances were produced, which gave amino acids after acid-hydrolysis. Major part of "amino acid precursors" were not simple molecules like aminonitriles, but complex compounds which eluted earlier than free amino acids in cation-exchange HPLC. These organic compounds should be major targets in the future Mars mission. Strategy for the detection of the complex organics on Mars will be discussed.     

Formation of bioorganic compounds in simulated planetary atmospheres by high energy particles or photons.

Various types of organic compounds have been detected in Jupiter, Titan, and cometary coma. It is probable that organic compounds were formed in primitive Earth and Mars atmospheres. Cosmic rays and solar UV are believed to be two major energy sources for organic formation in space. We examined energetics of organic formation in simulated planetary atmospheres. Gas mixtures including a C-source (carbon monoxide or methane) and a N-source (nitrogen or ammonia) was irradiated with the followings: High energy protons or electrons from accelerators, gamma-rays from 60Co, UV light from a deuterium lamp, and soft X-rays or UV light from an electron synchrotron. Amino acids were detected in the products of particles, gamma-rays and soft X-rays irradiation from each gas mixture examined. UV light gave, however, no amino acid precursors in the gas mixture of carbon monoxide, nitrogen and nitrogen. It gave only a trace of them in the gas mixture of carbon monoxide, ammonia and water or that of methane, nitrogen and water. Yield of amino acid precursors by photons greatly depended on their wavelength. These results suggest that nitrogen-containing organic compounds like amino acid precursors were formed chiefly with high energy particles, not UV photons, in Titan or primitive Earth/Mars atmospheres where ammonia is not available as a predominant N-source.     

Evolution of anticodons

Anticodons are trinucleotides in transfer RNA (tRNA) molecules. The latter carry amino acids for insertion into the polypeptide sequences of proteins during the translation of messenger RNA (mRNA) molecules. Messenger RNA molecules are transcribed from genes. Evolution of tRNA molecules has resulted in a set of anticodons for the 20 amino acids that are used in protein synthesis. This set of anticodons is slightly different in mitochondrial codes from the set that is used in the nuclear “universal” code. Theories for the evolution of the code include frozen accident, doublet expansion, repeating triplets and coevolutionary distribution. The number of codons has always been fixed at 64 by mathematical rules, but because an anticodon may pair with more than one codon, the number of anticodons is only 54 in the universal code, is smaller in mitochondrial codes, and was probably even smaller in archetypal primitive codes. Evidence of anticodon evolution can be seen by comparing mitochondrial codes with the universal code. Codes used by very primitive organisms that are now extinct might have specified fewer amino acids than are now used.     

Study of the peptide prebiotic synthesis in context of exobiological investigations on earth orbit.

Dry films of amino acids mixtures glycine+ tryptophan and tryptophan were exposed on the surface of "Mir" station. Similar films were irradiated by vacuum ultra violet (145 nm) and ultra violet (254 nm) in the laboratory experiments. Gly-Gly, Trp-Gly, Gly-Trp, Tpr-Trp and Trp-Trp-Trp were the main reaction products for the experimental mixture glycine + tryptophan and Tpr-Trp and Trp-Trp-Trp for tryptophan. The presence of Lunar soil both in flight and in laboratory experiments increases the reaction yield by 1.5-2.0 times. Therefore, the hypothesis concerning the possibility of safe delivery of peptides and amino acids required for the emergence of life and associated with mineral have got yet another approval.     

基于免疫抗体编码机理的卫星图像云探测

针对卫星遥感图像中云与下垫面的复杂性和多样性,提出了一种新的在复杂背景下常用目标图像描述方法.通过类比生物免疫抗体特异性与其构成单元氨基酸性质的相关性,得到目标图像的免疫基元集合形式及其分类方法.借鉴生物免疫抗体编码顺序中氨基酸结合能量最小原则,统计分析出训练样本的免疫基元亲和度计算公式,实现了目标图像描述的有限多特征优化组合.对于云检测问题,最终提出云的免疫抗体编码方法,定义了云的免疫亲和度计算公式,并成功构建了云免疫抗体.经200幅IKONOS卫星图像测试,验证了该方法在识别率和运行时间效率方面的有效性.      

Transport of extraterrestrial biomolecules to the Earth: problem of thermal stability.

The idea of extraterrestrial delivery of organic matter to the early Earth is especially attractive at present and is strongly supported by the detection of a large variety of organic compounds, including amino acids and nucleobases, in carbonaceous chondrites. Whether these compounds can be delivered by other space bodies is unclear and depends primarily on capability of the biomolecules to survive high temperatures during atmospheric deceleration and impacts to the terrestrial surface. In the present study we estimated survivability of simple amino acids (alpha-aminoisobutyric acid, L-alanine, L-valine and L-leucine), purines (adenine and guanine) and pyrimidines (uracil and cytosine) under rapid heating to temperatures of 400 to 1000 degrees C under N2 or CO2 atmosphere. We have found that most of the compounds studied cannot survive the temperatures substantially higher than 700 degrees C; however at 500-600 degrees C, the recovery can be at a per cent level (or even 10%-level for adenine, uracil, alanine, and valine). Implications of the data for extraterrestrial delivery of the biomolecules are discussed.     

Characterization of complex organic compounds formed in simulated planetary atmospheres by the action of high energy particles.

A wide variety of organic compounds, which are not simple organics but also complex organics, have been found in planets and comets. We reported that complex organics was formed in simulated planetary atmospheres by the action of high energy particles. Here we characterized the experimental products by using chromatographic and mass spectrometric techniques. A gaseous mixture of CO, N2 and H2O was irradiated with high energy protons (major components of cosmic rays). Water-soluble non-volatile substances, which gave amino acids after acid-hydrolysis, were characterized by HPLC and mass spectrometry. Major part of the products were complex compounds with molecular weight of several hundreds. Amino acid precursors were produced even when no water was incorporated with the starting materials. It was suggested that complex molecules including amino acid precursors were formed not in solution from simple molecules like HCN, but directly in gaseous phase.     

Controlled environments alter nutrient content of soybeans.

Information about compositional changes in plants grown in controlled environments is essential for developing a safe, nutritious diet for a Controlled Ecomological Life-Support System (CELSS). Information now is available for some CELSS candidate crops, but detailed information has been lacking for soybeans. To determine the effect of environment on macronutrient and mineral composition of soybeans, plants were grown both in the field and in a controlled environment where the hydroponic nutrient solution, photosynthetic flux (PPF), and CO2 level were manipulated to achieve rapid growth rates. Plants were harvested at seed maturity, separated into discrete parts, and oven dried prior to chemical analysis. Plant material was analyzed for proximate composition (moisture, protein, lipid, ash, and carbohydrate), total nitrogen (N), nonprotein N (NPN), nitrate, minerals, amino acid composition, and total dietary fiber. The effect of environment on composition varied by cultivar and plant part. Chamber-grown plants generally exhibited the following characteristics compared with field-grown plants: 1) increased total N and protein N for all plant parts, 2) increased nitrate in leaves and stems but not in seeds, 3) increased lipids in seeds, and 4) decreased Ca:P ratio for stems, pods, and leaves. These trends are consistent with data for other CELSS crops. Total N, protein N, and amino acid contents for 350 ppm CO2 and 1000 ppm CO2 were similar for seeds, but protein N and amino acid contents for leaves were higher at 350 ppm CO2 than at 1000 ppm CO2. Total dietary fiber content of soybean leaves was higher with 350 ppm CO2 than with 1000 ppm CO2. Such data will help in selecting of crop species, cultivars, and growing conditions to ensure safe, nutritious diets for CELSS.