Ion-exchange chromatography in lunar organic analysis

Although ion exchange chromatography has been used in separating amino acids from mineral salts, quantitative recovery has not been possible for the basic amino acids or for subnanomole concentrations of amino acids.As an analytical tool for amino acid analysis, ion-exchange chromatography has made it possible to resolve a relatively complex mixture of amino acids in less than an hour with detection limits of less than 10^–12 moles of amino acids. Reasonable specificity for amino acids is achieved by multiple wavelength detection of the reaction product found with ninhydrin. Unequivocal specificity must be obtained in conjunction with other methods such as mass spectrometry.In the analysis of subnanomole levels of amino acids, it is necessary to carry both reagent blanks and low-level amino acid standards through the entire sample preparation step since both contamination and selective losses occur and must be monitored.     

Transport and utilization of free fatty acids in Triatoma infestans

Triatoma infestans hemolymph has 0.31 mg/ml of free fatty acids and 2.8 mg/ml of diacylglycerols. Almost all the diacylglycerols are transported by lipophorin whereas free fatty acids are carried by lipophorin and a very high density lipoprotein. The binding of cis-parinaric acid to lipophorin was employed to specify the free fatty acid binding properties of lipophorin. Lipophorin has 10 binding sites of high affinity (3 x 10(7)) and approximately 45 binding sites of low affinity (1 x 10(6)). The relative rate of tissue incorporation of free fatty acids and diacylglycerols was measured by injecting insects with hemolymph previously labeled in both, free fatty acids and diacylglycerols. In this way, the half-life of the hemolymph free fatty acids was estimated to be about 4 min. Based on this result and taking into account the content of free fatty acids and diacylglycerols in hemolymph, the incorporation of free fatty acids, expressed in moles of fatty acids, seems to be 3.4 times higher than that of diacylglycerols. This finding can be applied to other insects.     

Problems in the search for amino acids in lunar fines

In the search for amino acids in lunar fines, a major problem is the prevention of contamination from terrestrial sources, and the recognition of terrestrial contamination when it has occurred. Synthesis of amino acids conceivably could take place in the lunar module rocket exhaust, a possibility that has not been adequately ruled out. Amino acids could be shed from the astronauts suits, a possibility which has not been studied at all. Amino acids could also be introduced, at many stages of terrestrial manipulation, and during the analytical procedures employed. Hand contamination has qualitative and quantitative features that are characteristic and can be assessed. Precautions for elimination of hand and microbial contamination from glassware, reagents and water are proposed.A second major problem is the efficiency of recovery of amino acids added to lunar material, which is then subject to the complete analytical scheme. This necessitates the availability of lunar material to develop proper procedures.Besides the amino acids present in excess of blank values, it is necessary for the correct interpretation of any positive findings to know whether the amino acids are free or bound and optically inactive or active.The ion exchange chromatography and gas chromatography-mass spectrometry are procedures that complement each other. Both should be applied not only to the same sample but to the same preparations. To pit one method against the other is to risk losing the best analytical data.     

Study of the natural antihistamine-like substance in bile in mammals.

A natural antihistamine substance (NAS) present in bile has been investigated. It was found that the antihistamine activity was not due to proteins, lipids, pigments, or amino acids. On ion exchange chromatography and thin-layer chromatography, this activity was associated with bile acids. Many bile acids could, in varying degrees, inhibit this histamine induced guinea pig ileum contraction, desoxycholic acid being the most potent. However NAS activity could be separated from bile acids and their conjugates using a different solvent system. Furthermore, NAS showed a higher antihistamine activity than bile acids. This substance seems to be responsible for 15-20% of the activity of whole bile. The substance has not yet been identified.     

alpha,alpha'-disubstituted amino acids with silylated side chains as lipophilic building blocks for the synthesis of peptaibol analogues

New alpha,alpha'-disubstituted amino acids with silylated side chains have been synthesized in racemic form. Starting from a Schiff base of glycine tert-butyl ester, a large variety of alpha,alpha'-dialkylated amino acids has been obtained, depending on the alkylating reagents. The application of a hydrosilylation methodology enabled the synthesis of the same unnatural amino acids in an enantiomerically pure form. The ability of these bulky amino acids to be incorporated into peptides by solution-phase methodology has also been demonstrated, since constrained silylated dipeptides have been synthesized. These new lipophilic building blocks could be useful and innovative in the design of peptaibol analogues.     

利用酵母菌生产有机酸的研究进展

有机酸是含有一种或多种低分子量酸性基团(如羧基、磺酸基)的可生物合成的有机化合物,广泛应用于食品、农业、医药、生物基材料工业等领域。酵母菌具有生物安全、抗逆性强、底物谱广泛、方便遗传改造,以及大规模培养技术成熟等独特优点,因此利用酵母菌生产有机酸的研究日益受到国内外学者的关注。目前利用酵母生产有机酸还存在浓度低、副产物多,以及发酵效率低等缺陷。随着酵母菌代谢工程和合成生物学技术的发展,利用酵母菌生产有机酸取得了快速进展。本文总结了利用酵母合成11种有机酸的研究,包括内源和异源合成的大宗羧酸和高价值有机酸,并对该领域的未来研究方向进行了展望。     

Bioavailability of phenolic acids

Two large classes of phenolic acids were comprised in this review: benzoic acid derivatives and cinnamic acid derivatives. They have been found to be very extended in fruits and vegetables at different concentrations. For example, hydroxycinnamic acids concentration was higher than that found for hydroxybenzoic acids. Concerning their consumption, hydroxycinnamic acids provide larger contributions to the total polyphenol intake than benzoic acid derivatives or flavonoids. This phenolic acid intake is led by the coffee intake since it has very rich concentrations in hydroxycinnamic acids. Moreover, several experimental and epidemiological studies report the protection of phenolic acids against various degenerative diseases. However, despite all these interesting attributions and even if phenolic acids are the main polyphenols consumed, their bioavailability has not received as attention as that flavonoids. This concept is an essential step to understand the health-promoting properties of phenolic acids and to serve as tool to design in vivo and in vitro experiments to know their biological properties. Therefore, a compilation of bioavailability data of phenolic acids have been presented here paying attention to the two types of phenolic acid bioavailability, direct and indirect derived from the direct phenolic acid and flavonoid consumption, respectively. Then, a new relevant concept which may be named as total bioavailability of phenolic acids includes the direct absorption and metabolism of phenolic acids from food consumption and phenolic acids bioavailability as a result of the cleavage on the main skeleton ring of flavonoids by the gut microflora.     

植物对氨基酸的吸收及其生理效应

<正> 在古代的农业系统中,所用的肥料都是有机肥,人们并不知道植物依赖于何种物质得以生长繁衍。自1840年,德国化学家李比希(J.U.Liebig)发表了《化学在农业和植物生理学上应用》一书后,人们对植物的营养有了新的认识,认识到矿物质对植物的重要性。李比希在书中指出:“土壤中矿物质是一切绿色植物唯一的养料。植物可以完全依赖于无机物质而生长发育。这一观点即为“植物的矿质营养学说”。该学说后来为生产实践所充分证明,并成为农业化学     

Comparison of the frequency of functional SH3 domains with different limited sets of amino acids using mRNA display

Although modern proteins consist of 20 different amino acids, it has been proposed that primordial proteins consisted of a small set of amino acids, and additional amino acids have gradually been recruited into the genetic code. This hypothesis has recently been supported by comparative genome sequence analysis, but no direct experimental approach has been reported. Here, we utilized a novel experimental approach to test a hypothesis that native-like globular proteins might be easily simplified by a set of putative primitive amino acids with retention of its structure and function than by a set of putative new amino acids. We performed in vitro selection of a functional SH3 domain as a model from partially randomized libraries with different sets of amino acids using mRNA display. Consequently, a library rich in putative primitive amino acids included a larger number of functional SH3 sequences than a library rich in putative new amino acids. Further, the functional SH3 sequences were enriched from the primitive library slightly earlier than from a randomized library with the full set of amino acids, while the function and structure of the selected SH3 proteins with the primitive alphabet were comparable with those from the 20 amino acid alphabet. Application of this approach to various combinations of codons in protein sequences may be useful not only for clarifying the precise order of the amino acid expansion in the early stages of protein evolution but also for efficiently creating novel functional proteins in the laboratory.     

A simple and rapid method of quantitative analysis of phosphoamino acids by high-performance liquid chromatography

A high-performance liquid chromatographic system for the separation of nonradiolabeled phosphoamino acids and orthophosphate by ion-pair reverse-phase chromatography has been developed. By the use of low-ionic-strength phthalate buffers at pH 6.3, the phosphoamino acids can be visualized by virtue of this uv-active eluant. The technique is sensitive to 200 pmol of phosphoamino acid and has been shown to be directly applicable to the analysis of isolated phosphoproteins.     

STUDIES OF THE INTER-RELATIONSHIP BETWEEN CEREBROSPINAL FLUID AND PLASMA AMINO ACID CONCENTRATIONS IN NORMAL INDIVIDUALS

Abstract— —The concentration of free amino acids has been determined in lumbar CSF in 37 fasting normal subjects. The values obtained have been compared with the concentration of the same amino acids measured in venous plasma collected simultaneously and with ventricular CSF amino acid concentrations. Twenty-three amino acids have been identified and quantitated in CSF and plasma. Trace quantities of eight other amino acids have been also detected.
The concentration of 13 amino acids in CSF has been shown to be directly related to the plasma concentration. No such relationship was noted for the other 7 amino acids. Significant variations in the concentration of individual amino acids relating to both age and sex have been noted. A large number of unidentified ninhydrin positive compounds have been found in CSF. Preliminary studies have identified one of these as ɛ-aminobutyric acid (GABA).     

Analysis of glycated amino acids by high-performance liquid chromatography of phenylthiocarbamyl derivatives

A method has been developed for the analysis of hexitolamino acids formed by acid-catalyzed hydrolysis of nonenzymatically glycated proteins that have been treated with sodium borohydride. The hexitolamino acids are converted into phenylthiocarbamyl (PTC) derivatives which are analyzed by reverse-phase HPLC. The PTC derivatives of N alpha-hexitolamino acids behave like lactones, migrating on the column more slowly than the corresponding PTC-amino acids. The PTC derivatives of N epsilon-glucitol- and N epsilon-mannitol-lysine are probably free acids, since they migrate faster than PTC-lysine. The method, which can be used to determine the degree of glycation of N-terminal and lysyl residues, has been applied successfully to human hemoglobin, serum albumin, and ocular lens proteins.     

Hydropathic anti-complementarity of amino acids based on the genetic code

An interesting pattern in the genetic code has been discovered. Codons for hydrophilic and hydrophobic amino acids on one strand of DNA are complemented by codons for hydrophobic and hydrophilic amino acids on the other DNA strand, respectively. The average tendency of codons for "uncharged" (slightly hydrophilic) amino acids is to be complemented by codons for "uncharged" amino acids.     

Synthesis of fatty acids, in vitro by choline-deficient and normal larvae of the housefly, Musca domestica

The synthesis of long chain fatty acids from acetate by a de novo pathway and by direct elongation of endogenous fatty acids has been demonstrated in homogenates of 4-day-old housefly larvae. The distribution of the synthesized fatty acids among the main classes of lipid has been studied. Addition of coenzyme-A to the medium inhibited the de novo synthesis pathway and made elongation the main synthetic route by which the radioactive acetate was incorporated into fatty acids. Direct elongation of palmitoleic to vaccenic acid has been demonstrated to occur in the homogenates. No consistent differences could be observed in the amount and distribution of the radioactivity incorporated into the fatty acids of homogenates prepared from larvae reared on a choline-deprived or a choline-sufficient diet. Addition of phosphatidylcholine to such homogenates also produced no changes in the labelling patterns. It was concluded that the changes seen, in vivo, in the fatty acids of the phospholipids, which accompany alteration of the amount of lipid-choline in the larvae, were unlikely to be due to any direct effect of the phosphatidylcholine on the enzymes involved in fatty acid synthesis.     

Transfer of maternal plasma free fatty acids into the rat fetus.

The amount of maternal plasma free fatty acids passing to the fetus has been determined to be 0.09 mumoles fatty acids per min per each litter. Taking account of the increase of the total fetal fatty acid pool due to the fetal growth (0.2 mumoles fatty acids per min for each litter) we conclude that the maternal circulation is the source of about half of fetal fatty acids on day 21 of pregnancy.     

酚酸类物质的化感作用研究进展

酚酸类物质是普遍存在于高等植物组织并与植物生长密切相关的次级代谢产物。几十年来,人们对酚酸类化合物的认识逐渐加深,但关于其在生物学、生态学以及农业上的作用机制仍不是很清楚。因此,进一步了解这些生物分子将有助于生态系统的维持与保护。重点介绍了酚酸类物质的来源及化感作用,微生物对酚酸类物质的降解机理,代谢途径及相应分子水平的研究,指出了酚酸类物质研究中存在的问题,同时展望了酚酸类物质的研究方向与前景。     

Dietary influences on serum lipids and lipoproteins

Substantial data are available to indicate that the diet influences serum levels of cholesterol and lipoproteins. These data are derived from studies in laboratory animals, from epidemiologic studies, and from human investigations. Most research has focused on effects of diet on serum total cholesterol concentrations. In recent years, however, attention has shifted to individual lipoproteins, i.e., low density lipoproteins (LDL), high density lipoproteins (HDL), and very low density lipoproteins (VLDL). Three nutritional factors have been identified that raise serum LDL levels; these are saturated fatty acids, cholesterol itself, and excess caloric intake leading to obesity. The major cholesterol-raising saturated fatty acid in the diet is palmitic acid. Several nutrients can be substituted for saturated fatty acids to produce a reduction in LDL-cholesterol levels. These are polyunsaturated fatty acids, monounsaturated fatty acids, carbohydrates, and even one saturated fatty acid, stearic acid. The latter appears to be converted rapidly into a monounsaturated fatty acid in the body. Any of these nutrients can be used for replacement of cholesterol-raising saturated fatty acids in the diet. However, their relative effects on other metabolic processes remain to be determined fully. At present it appears that carbohydrates and monounsaturated fatty acids represent the preferred replacements for saturated fatty acids, although modest increases in polyunsaturated fatty acids and stearic acid, at the expense of cholesterol-raising saturates, probably are safe and may provide for greater variety in the diet.     

Rayleigh light scattering study on the reaction of nucleic acids and methyl violet

A new quantitative determination method for nucleic acids in aqueous solutions, based on the enhancement of Rayleigh light scattering of methyl violet by nucleic acids, has been developed. The sensitivity of the assay allows amounts of nucleic acids as little as 100 ng/ml to be quantitated reliably. In addition to its high sensitivity, this method has other advantages: rapidity of reaction (<5 min), simplicity of operation (one-step assay), commonality of spectrofluorimeter and reagents, stability of mixtures formed, and reproducibility. Under the experimental conditions, there is little or no interference from proteins, nucleosides, and most metal ions. Interference by a few metal ions, detergents, and some salts can be minimized by dilution. The method can also be used to determine the total amount of nucleic acids without the arduous choice of standard and difficult separation of DNA and RNA.     

Interaction of alpha-tocopherol with free fatty acids. Mechanism of stabilization of lipid bilayer microviscosity

Using ESR-spin probes and 1H-NMR-spectroscopy methods the effect of alpha-tocopherol on liposome microviscosity has been studied. alpha-Tocopherol has been shown to remove the chaotropic action of free fatty acids on bilayer. The stabilization effect found has a common nature and does not depend on the chemical structure of the phopsholipid functional polar groups, the unsaturation degree of free fatty acids as well as fatty acids residua entering into phospholipid composition. Analog of alpha-tocopherol without phytol chain 2,2,5,7,8-penthamethyl-6-oxychroman does not show the stabilizing effect on the microviscosity of lipid bilayer under the action of free fatty acids. It indicates that both chromanol nucleus and phytol chain of alpha-tocopherol molecule are necessary for stabilizing action. The data obtained allow to suppose that the interaction of alpha-tocopherol with free fatty acids may be one of the molecular mechanisms of lipid bilayer microvicosity stabilization.     

Application of hierarchical thermodynamic interactions to the protonation equilibria of organic polyprotic acids

A general method for formulating complex thermodynamic systems in terms of hierarchical interactions has been developed, and has been applied in a previous analyses to the theoretical analysis of cooperativity in a dimeric protein, to the statistical analysis of hemoglobin oxygen binding data, and to the protonation equilibria of inorganic polyprotic acids. Organic polyprotic acids have served as a demonstration system for the development of concepts and methods for treating complex biochemical equilibria. Glutamic acid is the classic test case for understanding proton-proton interactions in organic polyprotic acids, and this system is analyzed using the concept of hierarchical interactions. Second order interactions were apparent between all three possible proton interactions, as has been established previously. The third order interaction between the three protons was found to be insignificant, indicating that protonation of one site on glutamate has no effect on the interaction between the other two protonation sites. This further reinforces the premise that higher order terms, representing more complex interactions, are less likely to be significant than lower order terms. To allow correlation of the interaction values from glutamate with other organic acids, pairwise interaction values between protonation events were then calculated from known pKd values for a number of diprotic acids and bases. For simple straight chain acids and bases a linear log-log relationship was apparent between the number of intervening atoms between the protons and the pK(d,hh) (pKd of interaction). This relationship extended from three atoms (carbonate) up to 11 atoms (azelaic acid) and applied to both dicarboxylic acids and diamine bases. The pairwise interactions in glutamate also followed this simple relationship.