Fixation of molecular tritium by bacterial suspensions

1.

1. Tritium can be oxidized to water apparently through the activity of the enzyme hydrogenase.     

Tritium isotope effects in the reaction catalyzed by 4-hydroxyphenylpyruvate dioxygenase from pseudomonas sp. strain P.J. 874

Tritium isotope effects in the reaction catalyzed by 4-hydroxyphenylpyruvate dioxygenase (4-hydroxyphenyl-pyruvate:oxygen oxidoreductase (hydroxylating, decarboxylating), EC 1.13.11.27) from Pseudomonas sp. strain P.J. 874 were studied with 14C- and different 3H-labelled 4-hydroxyphenylpyruvate. Tritium of ring-2,6-3H2-labelled substrate was released into water in 1:2 stoichiometry to 14CO2 formation. The tritium release from ring-3,5-3H2- and side chain-3-3H1-labelled 4-hydroxyphenylpyruvate was low as compared with 14CO2 formation. The apparent tritium isotope effects were below two, as judged by comparison of 3H/14C ratios of 4-hydroxyphenylpyruvate and homogentisate. The ratios showed no dependence on oxygen concentrations between 1 and 21% in the gas phase. Thus, a tritium assay can be used to determine the activity of 4-hydroxyphenylpyruvate dioxygenase. Apparently, none of the substrate hydrogens is involved in any rate-limiting step up to the first irreversible step. enol-4-Hydroxyphenylpyruvate was excluded as the active substrate tautomer.     

小麦A，B和D基因组同源DNA序列在进化过程中的演变研究

选取已定位的大麦1H染色体的STS标记NWG913为引物,在普通小麦（Tritium aestivum L.）及其4个可能的起源种乌拉尔图小麦（T.urartu T.)、栽培一粒小麦（T.monococcum.L)栽培二粒小麦（T.dicoccum S.）、方穗山羊草（Ae.squarrosa L.)上特异性扩增。扩增产物克隆测序后对其进行序列分析,由序列差异的程度来确定这几个物种之间的亲缘关系。实验结果表明,普通小麦（Tritium aestivum L.)的A基因组此段序列与乌拉尔图小麦（T.urartu T.)、栽培一粒小麦（T.monococcum L.)、栽培二粒小麦（T.dicoccum S.)A基因组此段序列完全相同;普通小麦的D基因组此段序列与方穗山羊草（Ae.squarrosa L.)也完全相同;普通小麦的B基因组此段序列和栽培二粒小麦B基因组此段序列有0．61％的差异。研究结果一方面对现有的普通小麦A、B、D基因组起源和进化理论给予了分子水平上的证明,同时也揭示了同一物种不同的基因组化进化速度存在差异。     

Stereochemical analysis of the elimination reaction catalyzed by D-amino-acid oxidase.

The stereochemistry of the intramolecular proton transfer catalyzed by the flavoenzyme, D-amino-acid oxidase, during the elimination reaction of beta-chloro-alpha-amino acid substrates (Walsh et al. (1973), J. Biol. Chem. 248, 1964) has been established. Both D-erythro- and D-threo-2-amino-3-chloro(2-3H) butyrate have been shown to yield (3R)-2-keto (3-3H)-2- butyrate predominantly. Tritium kinetic isotope effects on the rate of the reaction (4.7 for the D-erythro, and 3.8 for the D-threo compound) and percentages of intramolecular triton transfer (7.2% for the D-erythro- and 2.6% for the D-threo compound) have been measured. Their implications on the mechanism of this unusual elimination reaction are discussed.     

Tritium labeling of tRNA by the tritium thermal activation method

Tritium labelled E. coli total tRNA and tRNAPhe are prepared by action of thermally activated tritium atoms. The preparations, having the molar radioactivity up to 3.6 Ci/mmol, are useful for functional investigations.     

Historical changes in the conductivity and ionic charateristics of the source water for the Shark River Slough,Everglades National Park,Florida, U.S.A.

Man-made changes in the hydrological regime of South Florida have significantly altered the conductivity and ionic composition of water in the Shark River Slough system of Everglades National Park. The shift in water inputs from unregulated marsh water flow to regulated delivery of canal water has resulted in a 140% increase in conductivity and 149% increase in total ionic concentration since the early 1960s. Associated with this change has been a 300–400% increase in sodium and chloride concentrations in the waters entering the Shark River Slough of Everglades National Park.     

Synthesis of [24, 25-3H]cholesterol: a new substrate for determining the rate of cholesterol side chain oxidation.

A procedure for the synthesis of [24,25-3H]cholesterol from the nonradioactive precursor desmosterol is described. The intermediate, isodesmosterol, which was purified by column chromatography, was formed to protect the original double bond (delta 5-6) from hydrogenation. Tritium was introduced into the side chain by catalytic reduction of the double bond (delta 24-25) of the isodesmosterol in the presence of carrier-free tritium. After ring rearrangement of the iso-[24,25-3H]cholesterol acetate, the acetate was hydrolyzed to form the free labeled cholesterol. Hepatic oxidation of the [24,25-3H]cholesterol side chain release tritium into water which freely equilibrates with cell and body water pools. Thus, the rate of 3H2O appearance corresponds to the rate of cholesterol side chain oxidation. Applications of this method to in vivo, isolated perfused liver, and isolated hepatocyte preparations of the rat are discussed.     

Systematic review of experimental studies on the relative biological effectiveness of tritium

Tritium (³H) is a radioactive isotope of hydrogen. A number of factors combine to create a good deal of interest in tritium doses, both to workers and to members of the public. Tritium is ubiquitous in environmental and biological systems and is very mobile due to its occurrence as water. In this study we systematically review experimental data relating to tritium exposure with a view to assessing its low dose limiting relative biological effectiveness (RBE_max). Interpretation of published experimental studies is complicated by the fact that the reference radiations varied, and doses and dose rates were frequently much higher than those normally received by humans. The four available animal carcinogenicity studies gave RBE values of about 2.5 with chronically-delivered γ-ray reference, and about 1.2 with chronically-delivered X-ray reference. However, because of problems associated with the design and interpretation of the experiments, we do not consider that these RBE values should be taken to apply to the induction of cancer at low doses (i.e. they should not be interpreted as RBE_max). Combining the six studies with chronic γ-ray reference, with adequate quantitative data that examined endpoints apart from cell survival and related endpoints, yields an aggregate RBE estimate of 2.19 (95% CI 2.04, 2.33); the analogous combined RBE estimate using the three studies with chronic X-ray reference groups is 1.17 (95% CI 0.96, 1.39). Again, problems with the design, in particular the range of doses used in some of these studies, mean that these RBE values should also probably not be interpreted as RBE_max.     

Effect of water containing calcium and magnesium sulfates on the elimination of cholesterol in the rat

In the rat, the activity of the thermal water of Capvern and of its ionic components on the modification of the flow rate and composition of hepatic bile has been investigated. Two groups of rats were selected: the first group received per os an overload of the thermal water during six weeks. At that time on empty stomach a great increase of biliary phospholipids was observed. An intraduodenal injection of the thermal water produced a significant and rapid increase of biliary flow rate and biliary cholesterol. the animals of the second group received through intraduodenal injections the thermal water or an anionic solution composed of calcium, of magnesium sulphate or of both salts at their concentration in the thermal water, respectively. We observed an increase in biliary flow rate and biliary calcium concentration in the rats receiving the solution of calcium sulphate only and an increase of choleresis in the rats receiving the thermal water only. These data suggest that the thermal water has a specific action on the metabolism of cholesterol in increasing its biliary elimination particularly through the calcium ion content of the water.     

Molecular dynamics simulation of the spreading of the nanosized droplet on a graphene-coated substrate: the effect of the contact line forces

Surface characteristics of graphene have an important impact on its performance. Substantial attention has been devoted to studying the static wetting behaviour of a graphene-coated substrate with little attention to the dynamic wetting behaviour. The impact of contact line forces (CLFs) on the droplet-spreading process has not been revealed completely yet. A series of molecular dynamics (MD) simulation is performed to investigate the spreading process of the water droplet on the graphene-coated substrate in this research. The increase of interaction potential parameter between substrate and water droplet makes the spreading radius getting bigger and the final static contact angle smaller. Apart from that, the higher hydrophilicity of underlying substrate can lead to the greater averaged forces of atoms near contact line. CLFs correlate well with the variation of kinetic energy of water molecules located in the contact line region. Surface tensions of water droplets on graphene-coated substrates are also examined. The liquid-vapour and solid-vapour surface tensions are constant. An increase in the surface tension of liquid-solid lead to the increase of balanced contact angles of water on the substrate. The results are useful for understanding the effect of CLFs on the dissipation of kinetic energy of water molecules.     

Quantitative tritium exchange of [3H] aflatoxin B1 during penetration through isolated human skin

Tritium labelled aflatoxin B1 ([G-3H]AFB1) underwent an almost total tritium exchange with water during penetration through isolated human skin. The process was not enzymatic and the site of exchange appeared to be within the epidermis. The mechanism which mediated this extensive exchange was not determined. However, the tritium in [G-3H]AFB1 was found to be very susceptible to chemical conditions which favored carbanion formation at the alpha-carbon of the cyclopentenone ring. The relative effectiveness of the various solvents in mediating the loss of the tritium label was 1 N3NaOH much greater than methanol greater than 1 N HCl greater than water. This work serves as a warning that [G-3H]AFB1 can easily undergo significant changes in specific activity in biological tissues and under relatively mild experimental conditions. It is possible that conditions within the skin favor carbanion formation.     

Effect of NaCl on the exothermic and endothermic components of the inverse temperature transition of a model elastin-like polymer

TMDSC data have been employed to observe the effect of NaCl on the inverse temperature transition of the model elastin-like polymer (GVGVP)251. NaCl causes a decrease in Tt and an increase in DeltaH. The increase in enthalpy appears both in the enthalpy related with the folding of the polymer and in the contribution associated with disruption of the structured water of hydrophobic hydration. It has been suggested that the presence of NaCl may cause a better formation of water structures surrounding the apolar polymer chains.     

Influence of ecological factors on the growth of crustaceans from the genus Artemia in Ural and Siberian populations

A morphometric analysis of crustaceans from the genus Artemia inhabiting nine Ural and Siberian populations has been carried out. An effect of the total mineralization of water reservoirs and some ions on the characteristics of Artemia growth has been discovered. The number of setae on furca and its length are most affected by the factors under consideration. A trend toward a decrease in the manifestation of fluctuating asymmetry alongside an increase in the total mineralization of water reservoirs has been found.     

Nature of the stacking of nucleic acid bases in water: a Monte Carlo simulation

The results of a Monte Carlo simulation of the hydration of uracil and thymine molecules, their stacked dimers and hydrogen-bonded base pairs are presented. Simulations have been performed in a cluster approximation. The semiempirical atom-atom potential functions have been used (cluster consisting of 200 water molecules). It has been shown that the stacking interactions of uracil and thymine molecules in water arise mainly due to the increase in the water-water interaction during the transition from monomers to dimer. It has been found out that stacked base associates are more preferable than base pairs in water. This preference is mainly due to the energetically more favourable structure of water around the stack.     

Increase of water permeability and recovery of water impermeability of the frog urinary bladder

The experiments carried out on the urinary bladder of the frog Rana temporaria L. have shown that the period of recovery of water impermeability after an increase of osmotic water permeability induced by arginine-vasotocin, desmopressin, or cAMP depends on the degree of increase of the osmotic permeability but not on the nature of the substance stimulating the increase of osmotic water permeability. The removal of the hormone in the absence of autacoids fails to recover the water impermeability. After cessation of the vasotocin action the water permeability decrease is delayed if phospholipase A2 and cyclooxygenase are inhibited by qiunacrine and voltaren, respectively. An agonist of V1-receptors has no effect on dynamics of the recovery of water impermeability. This recovery has been shown to depend on PGE2 concentration in the serosal solution after the hormone removal. The obtained results indicate that decrease of water permeability depends not only on removal of vasotocin or cAMP but also on involvement of autacoids.     

Antibiotic Activity in the Presence of Agar

Agar has been shown to interfere with the activity of some antibiotics against Staphylococcus aureus. This interference has been observed as an increase in the minimal inhibitory concentration and in the diameter of the zone of inhibition. Purifying the agar with water extractions substantially reduced this adverse effect.     

Nature of the Stacking of Nucleic Acid Bases in Water: a Monte Carlo Simulation

Abstract

The results of a Monte Carlo simulation of the hydration of uracil and thymine molecules, their stacked dimers and hydrogen-bonded base pairs are presented. Simulations have been performed in a cluster approximation. The semiempirical atom-atom potential functions have been used (cluster consisting of 200 water molecules). It has been shown that the stacking interactions of uracil and thymine molecules in water arise mainly due to the increase in the water-water interaction during the transition from monomers to dimer. It has been found out that stacked base associates are more preferable than base pairs in water. This preference is mainly due to the energetically more favourable structure of water around the stack.     

Eggshell porosity and the water metabolism of the chick embryo

Chick embryos have been water stressed during the last week of incubation by either withdrawing 6 cm³ of allantoic fluid or by increasing shell porosity three to four fold. Despite the large increase in water loss from these eggs they were successfully incubated to produce hatchlings of apparently normal water content. The chicks produced by water deprivation were significantly smaller than controls and it appears that the growth of embryos is therefore modulated according to the metabolites available. If this interpretation is correct it suggests that the critical role of eggshell porosity in avian development has been over-emphasized.     

Calibration of the emulsion layers in quantitative electron microscopic autoradiography]

The quantitative results in electron microscope autoradiography are affected by many factors. The principal problem of this method is a low mechanization of all the operations made. This paper gives a short review of technical improvements. The use of a calibration permits to except those factors which exert their influence on the sensitivity of the method. Tritium sources were used for the determination of the sensitivity of the method.