C3/C4 vegetation evolution over the last 7.0 Myr in the Chinese Loess Plateau: evidence from pedogenic carbonate δC

The stable carbon and oxygen isotopic compositions of soil carbonate were measured on an eolian loess and red clay sequence at Lingtai, the Chinese Loess Plateau. This sequence is composed of 130 m of Tertiary red clay deposits with a basal age of 7.05 Ma overlain by 175 m of Pleistocene loess. In the field we identified ca. 110 carbonate nodule horizons in the red clay and 27 nodule horizons in the loess. These carbonate nodule horizons are formed by leaching and re-precipitation of carbonate from the eolian material. The δ¹³C record of soil carbonate indicates a major expansion of C₄ plants at ca. 4.0 Myr in the Loess Plateau. This event is comparable in timing with the expansion of C₄ plants in northern North America (Cerling et al., 1997. Nature 389, 153–158) but is ca. 3 million years later than the C₄ biomass expansion in Pakistan (Quade et al., 1989. Nature 342, 163–166). The pedogenic characteristics of the soils and the δ¹⁸O record in the red clay suggest that the C₄ plant expansion in the Loess Plateau was not driven by local climatic changes, which may support Cerling et al.'s (1997) assertion that the decline of atmospheric CO₂ levels in the Neogene is responsible for this global vegetation change. Our record also implies that the Tibetan Plateau could have been uplifted to a critical height in the late Miocene, thus resulting in the formation of the atmospheric Great East-Asia Trough.     

On intrapersonal reciprocity

The existence of conflicts between different sets of genes within the genome is now widely accepted. But where there is conflict, there are also benefits to be gained from cooperation between the contending parties to reduce conflict costs. The potential for reciprocal altruism [Trivers, 1971] within an individual organism has hitherto attracted little attention but raises the possibility of complex interactions within the self.     

Retrotransposons: central players in the structure, evolution and function of plant genomes

One class of mobile DNA, the retrotransposons, constitutes a major portion of all eukaryotic nuclear genomes (often half of the total DNA), and has made a significant contribution towards the genome rearrangements that give rise to altered gene order and novel gene regulation. Research on plant retrotransposons is supported in only a handful of laboratories worldwide, but their progress continues to be striking, as shown at a recent workshop¹.     

Synthesis, characterization and crystal structures of nickel complexes with dissymmetric tetradentate ligands containing a mixed-donor sphere

Four new nickel(II) complexes of dissymmetric tetradentate ligands, containing mixed-ligand donor sets of NSNS or NSNO, have been synthesized. These complexes were prepared by facile template reactions of the appropriate aldehyde and amine in the presence of [Ni(H₂O)₆](BF₄)₂, resulting directly in the desired nickel compounds. The nickel compounds were characterized by analytical, spectroscopic and electrochemical methods. The structures of [Ni(pyzs)]BF₄, [Ni(pyrs)]BF₄ and [Ni(pyzo)]BF₄ (see Scheme 1) have been determined by single-crystal X-ray crystallography, showing the geometry of the nickel ion to be square-planar. Vis–NIR spectra show that the phenolate-containing complexes [Ni(pyzo)]BF₄ and [Ni(pyro)]BF₄ (see Scheme 1) are essentially square-planar in nitromethane, but tetragonal octahedral in methanol, whereas the thiophenolate-containing compounds [Ni(pyzs)]BF₄ and [Ni(pyrs)]BF₄ remain square-planar in both solvents. Titration of the thiophenolate-containing complexes with 1-methylimidazole results in diamagnetic five-coordinated complexes. Electrochemistry shows quasi-reversible reductions to Ni(I) to occur for [Ni(pyzo)]BF₄, [Ni(pyrs)]BF₄ and [Ni(pyro)]BF₄.     

A hydrodynamic study of the depolymerisation of a high methoxy pectin at elevated temperatures

The hydrodynamic properties (intrinsic viscosity, [η]; infinite dilution sedimentation coefficient, s_20,w⁰; weight average molecular weight, M_w and translational frictional ratio, f/f₀) of a high methoxy pectin have been evaluated at various temperatures (20–60°C). A reduction in the value of all four hydrodynamic parameters is indicative of depolymerisation and is in agreement with an earlier study using viscometry [Axelos, M.A.V., & Branger, M., (1993). Food Hydrocolloids, 7, 91–102]. The apparent linearity of the Mark – Houwink plot of log[η] vs log M_w suggests that the conformation of the pectin molecule does not change significantly over the temperature range studied. The evaluation of the Mark–Houwink viscosity exponent (a=0.84) indicates a moderately extended structure. This then allows the calculation of the number of Kuhn statistical lengths per chain from the adapted ‘blob’ theory of Dondos [Dondos A. (2001). Polymer, 42, 897–901]. The weight average number of Kuhn statistical lengths per chain is reduced from (170±10) to (125±10) when the temperature is increased from 20–60°C. This may be of significance as many high methoxy pectins are exposed to high temperatures during processing in both the food and pharmaceutical industries.     

Determination of the inorganic degradation products sulfate and sulfamate in the antiepileptic drug topiramate by capillary electrophoresis

A capillary electrophoresis (CE) method has been developed as an alternative method for the determination of the inorganic degradation products sulfate and sulfamate in topiramate drug product and drug substance, currently performed by ion chromatography. The anions are separated in a background electrolyte containing potassium chromate and boric acid, followed by indirect UV detection. By adding tetradecyltrimethylammonium bromide to the electrolyte, analysis is performed under co-electroosmotic flow conditions. Variations in injection volumes and migration times are compensated for by use of an internal standard. The validation of the method, which was performed according to ICH guidelines (International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use) [1], comprises specificity, accuracy, linearity, precision, sensitivity and robustness. In addition, the results of an actual tablet sample analysis obtained by this CE method are statistically shown to be in close agreement with those obtained by an ion chromatographic method.     

Lactones 27 [1]: Transformations of γ-lactones fused to a dimethylcyclohexane ring in Absidia cylindrospora cultures

Two saturated (4a,b) and one unsaturated (5) bicyclic γ-lactones containing a dimethylcyclohexane ring were subjected to biotransformation using the fungal strain Absidia cylindrospora. Six new compounds (6–11) and one known (12) [K.W. Rosenmund, H. Herzberg, H. Schutt, Chem. Ber. 87 (1954) 1258] [2] were isolated. All substrates were stereoselectively hydroxylated by the microorganism at either the C-4 (in the case of 4a and 5) or C-2 position (in case of 4a and 4b) giving the corresponding hydroxylactones with tertiary (6 and 9) or secondary (8 and 10) hydroxy groups, respectively.

The hydroxy group was also introduced into C-3 (in the case of 4a) and C-6 (in the case of 4b) positions. The structures of all obtained products were established on the basis of their spectral data. In the case of lactones 8–10 these structures were undoubtedly confirmed by their X-ray analysis.     

Activation of subtilisin Carlsberg in hexane by lyophilization in the presence of fumed silica

Subtilisin Carlsberg (SC) was lyophilized from an aqueous buffer solution containing different amounts of unmodified commercial fumed silica. The activity of the enzyme/fumed silica preparation in hexane was compared to pure freeze-dried enzyme, and to a freeze-dried preparation reported in the literature with potassium chloride as additive. A sharp increase in enzyme activity was found to correlate with an increasing amount of fumed silica added to the enzyme solution prior to freeze-drying. A weight-ratio of 98.5 wt.% fumed silica relative to the mass of the final enzyme/fumed silica preparation led to about 130-fold increased activity of SC in hexane (when compared to pure lyophilized SC in hexane). This is about twice the activation effect compared to including potassium chloride in the buffer solution before freeze-drying [1]. When freezing at −20 °C instead of in liquid nitrogen, even better activation was observed with fumed silica. We hypothesize that the activation of SC in hexane by immobilization of the enzyme on fumed silica is likely due to the distribution of the enzyme on the large surface area of fumed silica. This alleviates mass transfer limitations.     

Carbohydrate polymers in food preservation: an integrated view of the Maillard reaction with special reference to discoveries of preserved foods in Sphagnum-dominated peat bogs

Well-preserved human bodies more than 2000 years old have been found in peat bogs derived mainly from sphagnum mosses. Preservation is correlated with the occurrence of -keto-carboxylate groups in a glycuronoglycan (‘sphagnan') that comprises 60% of the holocellulose in the hyaline cell walls of the mosses [Painter (1991b). Carbohydr. Polym., 15, 123–142]. There is now renewed interest in other biodegradable materials that have been found preserved in peat, including carcasses of domestic animals, loaves of bread, dried fruits, berries, and kegs of butter or cheese up to 1800 years old. This review attempts to correlate these examples of fortuitous preservation in peat with other, more familiar methods of food preservation that depend in the first instance upon the condensation of highly reactive carbonyl compounds with primary amino-groups or ammonia. The Maillard reaction inhibits microbial growth by sequestering ammonia, aminoacids and peptides, while the brown, polymeric end-products (‘melanoidins') inhibit by cross-linking polypeptide chains and sequestering essential, multivalent metal cations. These reactions could find broader or entirely new applications in food preservation.     

Cloning of cDNA for Vitellogenin of the Parasitoid Wasp, Pimpla nipponica (Hymenoptera: Apocrita: Ichneumonidae): Vitellogenin Primary Structure and Evolutionary Considerations

The cDNA for vitellogenin (Vg) of the parasitoid wasp Pimpla nipponica (Hymenoptera: Apocrita) was cloned and sequenced.¹ The deduced amino acid sequence with 1807 residues was obtained. The N-terminal 20 amino acids chemically determined for vitellin (Vn) agreed completely with the deduced 20 amino acids that follow the 16 amino acid residues for putative signal peptide. The cDNA clone for the Vg of the turnip sawfly Athalia rosae (Hymenoptera: Symphyta), previously obtained and partially sequenced, was also completely sequenced and the amino acid sequence deduced. Amino acid sequences were compared between these two species and also with known Vg sequences from other insects. Common to all these insects is the presence of two long regions with relatively well-conserved amino acid sequences, one near the N-terminal extending 267–282 residues (including two cysteines at conserved locations), and the other starting at position 450 to 655 and extending 279–283 residues, and of a region at the C-terminal extending some 200 residues (about 250 in Aedes aegypti due to the presence of a serine-rich stretch) with 10 cysteines at conserved locations. A molecular phylogenetic tree was constructed.     

Spruce budworm elastase precipitates Bacillus thuringiensis δ-endotoxin by specifically recognizing the C-terminal region

A gut juice protein from Choristoneura fumiferana (spruce budworm) larvae that precipitates certain δ-endotoxins shows a unique specificity for the C-terminal amino acid sequence. Using homolog scanning mutants, we have identified a contiguous region of the Cry1Aa toxin which interacts with the 75-kDa toxin precipitating protein (TPP-75)¹ resulting in precipitation. The contiguous region from Cry1Aa can be transferred to Cry1Ac and results in an identical precipitation reaction. The precipitation reaction occurs rapidly and is unique in that the ratio of precipitating protein to toxin is low (estimated at 0.01), unlike antibody–antigen reactions which exhibit mole ratios close to 1. TPP-75 has been characterized as an elastase-like serine protease. We have taken advantage of this serine protease character and incorporated a radiolabel using an irreversible inhibitor. The radiolabel has allowed us to show the coincidence of the catalytically-inhibited TPP-75 with the toxin in a blotting assay and to follow the degradation of TPP-75 during storage. TPP-75 represents the first evidence that gut juice proteins may selectively attenuate the activity of δ-endotoxins, prior to binding to putative receptors on susceptible cells. TPP-75 should be evaluated as a possible resistance mechanism for those larvae that do not exhibit a receptor-based resistance.     

Modulation of serum testosterone and autonomic function through stimulation of the male human vomeronasal organ (VNO) with pregna-4,20-diene-3,6-dione

In mammals, external chemosensory signals from conspecifics of the opposite sex acting on vomeronasal organ receptors can modulate the release of gonadotropins. There is developmental, anatomical and functional evidence showing that the human vomeronasal organ (VNO) has the characteristics of a chemosensory organ. We have been using naturally occurring human pheromones to serve as models for designing novel synthetic compounds that we call vomeropherins². In previous publications we reported that vomeropherin pregna-4,20-diene-3,6-dione (PDD) delivered to the VNO of normal female and male human volunteers significantly affected male subjects only, decreasing respiration and cardiac frequency, augmenting alpha brain waves, and significantly decreasing serum luteinizing hormone (LH) and follicle stimulating hormone (FSH). Results of the present work confirm that PDD produces a local dose-dependent effect in the male human VNO. This is followed by a mild parasympathomimetic effect characterized by 10% increase of vagal tone, together with decreased frequency of electrodermal activity events. Furthermore, PDD locally delivered to the male human VNO significantly decreases serum LH and testosterone (p<0.01). The present results contribute additional evidence supporting the functionality of the human VNO and its repercussions in autonomic and psychophysiological functions, as well as in neuroendocrine secretions.     

Structure of a rhamnan from the surface-layer glyco-protein of Bacillus stearothermophilus strain NRS 2004/3a

The structure of a glycan from the surface-layer glycoprotein of Bacillus stearothermophilus strain NRS 2004/3a has been studied by ¹H- and ¹³C-n.m.r. spectroscopy. The results indicate the glycan to be a polymer of the trisaccharide repeating-unit

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Regio- and enantioselective reduction of methyleneketoesters mediated by Saccharomyces cerevisiae

Methyleneketoesters were readily prepared in high yields by performing a direct -methylenation of the corresponding ketoesters using a previously described protocol. Reactions of ethyl 2-methylene-3-oxo-3-arylpropanoates 2a–c catalyzed by S. cerevisiae were performed with good conversions to give reductions of the CC, CO or both, depending on the reaction conditions and on the substitution of the aryl moiety. Reaction of 3-methylene-2-oxo-4-phenylbutyrate 2d was carried out with free yeast cells and with yeast cells immobilized with calcium alginate, in which the major products resulted from CC and CO bond reduction.

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Synthesis of precursors for the dimeric 3-O-SO3Na Lewis X and Lewis A structures

Stereoselective syntheses of 3-O-SO₃Na-β-Gal-(1 → 4)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 4)-GlcNAc-β-OBn (15) and 3-O-SO₃Na-β-Gal-(1 → 3)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 3)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 4)-Glc-β-OBn (25) were accomplished through the use of two novel glycosyl donors, namely, ethyl

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(8) and ethyl

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(18).     

Synthesis of enantiomerically pure lysophosphatidylinositols and alkylphosphoinositols

A convenient synthesis for enantiomeric pure

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,

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(or and (or has been described. Starting from myo-inositol, penta-O-acetyl-myo-inositol was made in five steps. Then enantiomeric purification was done by a diastereomeric salts separation method, and the purity of each enantiomer was spectroscopically measured (¹⁹F-NMR). The phosphodiester was made via phosphoramidites. The enantiomeric products (>99% optical purity) of all compounds were easily obtained in large quantities (5–10 g). Synthetic phosphatidylinositol analogues of precisely defined structure and configuration are interesting tools for studying signal transduction mechanism and cell activity modulation.     

A stereocontrolled synthetic approach to glycopeptides corresponding to the carbohydrate-protein linkage region of cell-surface proteoglycans

The glycopeptides 1

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and 2

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), carrying the core structure of serine-linked cell-surface proteoglycans were synthesized in a stereocontrolled manner. The carbohydrate key imidate xylosyl donors 3 and glycotetraosyl donors 4 and 5, as well as a tetrapeptide glycosyl acceptor 6, were coupled in the crucial glycosylation step. In these reactions, the application of either trimethylsilyl trifluoromethanesulfonate (TMSOTf) or borontrifluoride etherate (BF₃-Et₂O) as catalysts proved to be highly efficient. The serine linked glycopeptides 34, 36 and 37 thus obtained yielded target compounds 1 and 2 on complete deprotection.     

The structure of the exopolysaccharide of Pseudomonas fluorescens strain H13

An acidic exopolysaccharide was isolated from P. fluorescens strain H13. The structure of the polysaccharide repeating unit was determined using chemical methods and 1D and 2D NMR techniques. The repeating unit was characterized as a trisaccharide composed of -glucose, 2-acetamido-2-deoxy- -glucose and

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acid.     

Structural studies of the O-antigen from Vibrio cholerae O:21

The O-antigen from Vibrio cholerae O:21 has been investigated, using n.m.r. spectroscopy, methylation analysis, and Smith degradation as the main methods. It is concluded that the O-antigen is composed of tetrasaccharide repeating-units having the following structure (in which Hep = -glycero- -manno-heptose).

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Effet de la longueur d'onde de préillumination sur la désactivation des formes oxydées du donneur d'électrons du Photosystème II

Effect of preillumination wavelength on the deactivation of oxidized forms of the Photosystem II electron donor

Deactivation was studied using chlorella cells or spinach chloroplasts after an illumination of different wavelengths (light I = 710 nm, light II = 650 or 480 nm). The measurements concerned mainly the third oxidized state S₃ of the System II electron donor, according to the scheme proposed by

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, (Photochem. Photobiol., 11 (1970)457). The time course of deactivation was followed during the dark after each preillumination. Different results were obtained with algae in state 1 or state 2 as defined by

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, (Biochim. Biophys. Acta, 189 (1969) 366). In state 1 the deactivation of S₃ is faster after light 11 than after light 1; in state 2, except at the beginning of the decay, the deactivation of S₃ is almost the same after the two kinds of preillumination. With chloroplasts the deactivation is slower, but always faster after light II than after light I, no transition between state 1 and state 2 was observed. The results are discussed with reference to the possible reducing substrates of the reaction.