Influence of D-galactosamine on the synthesis of sugar nucleotides and glycoconjugates in rat hepatocytes

Rat hepatocytes were incubated in the presence of a high concentrationof the hepatopathogenic agent D-galactosamine (GalN), and theeffect on the cellular concentrations of pyrimidine nucleotidesand nucleotide sugars was determined. The UTP pool became depleted.The pools of UMP and CMP in RNA decreased to 72%, indicativefor an inhibition of RNA synthesis. UDP-HexNAc (where HexNAcis GlcNAc + GalNAc) and UDP-HexN (where HexN is GlcN + GalN)levels increased, and those of UDP-hexose and UDP-GlcA (whereGlcA is glucuronic acid) decreased. The cellular concentrationof CTP did not change, whereas that of CMP-NeuAc (where NeuAcis N-acetylneuraminic add) showed a 2-fold increase. Labellingwith [¹⁴C]orotic acid and [³H]cytidine showed that the metabolicflow via the de novo pathway was not changed. The depletionof the so-called overflow pool of UTP [Pels Rijcken et al, Biochem.J., 293, 207–213, 1993] caused a release of the feedbackinhibition by UTP and thus an increased flow through the salvagepathway. Finally, it appeared that GalN, when added to hepatocytes,gives rise to a pool of UDP-GlcNAc (where GlcNAc is N-acetylglueosamine)that is separate from the pool of UDP-GlcNAc that is derivedfrom GlcN. D-galactosamine glycosylation sugar nucleotide biosynthesis     

Is hydrogen peroxide a second messenger of salicylic acid in systemic acquired resistance?

Elevated levels of salicylic acid (SA) are required for the induction of systemic acquired resistance (SAR) in plants. Recently, a salicylic acid-binding protein (SABP) isolated from tobacco was shown to have catalase activity. Based on this finding elevated levels of hydrogen peroxide (H₂O₂) were postulated to act as a second messenger of SA in the SAR signal transduction pathway. A series of experiments have been carried out to clarify the role of H₂O₂ in SAR-signaling. No increase of H₂O₂ was found during the onset of SAR. Induction of the SAR gene, PR-1, by H₂O₂ and H₂O₂-inducing chemicals is strongly suppressed in transgenic tobacco plants that express the bacterial salicylate hydroxylase gene, indicating that H₂O₂ induction of SAR genes is dependent on SA accumulation. Following treatment of plants with increasing concentrations of H₂O₂, a dose-dependent accumulation of total SA species was found, suggesting that H₂O₂ may induce PR-1 gene expression through SA accumulation. While the results do not support a role for H₂O₂ in SAR signaling, it is suggested that SA inhibition of catalase activity may be important in tissues undergoing a hypersensitive response.     

Aniline hydroxylase activities of haemoglobin: Kinetics and mechanism

The mechanism of the aniline hydroxylase activity of methaemoglobin in a monooxygenase system consisting of NADH as electron donor, riboflavin, FAD, FMN or methylene blue as electron carrier and methaemoglobin as the terminal oxidase has been studied. Hydrogen peroxide is produced from oxygen in a methaemoglobin-independent process. 4-Aminophenol is subsequently produced peroxidatively by an NADH-dependent process; NADH prevents a further oxidation of 4-aminophenol in the presence of haemoglobin. In the absence of electron carrier, NADH slowly reduces haemoglobin and then oxyhaemoglobin reacts with aniline to give 4-aminophenol. In the absence of electron donor and electron carrier, oxyhaemoglobin and aniline give rise to the reversible production of 4-aminophenol.     

Characterization and immunocytochemical demonstration of glucocorticoid receptor using antisera specific to transformed receptor

Cytosolic and nuclear forms of the glucocorticoid receptor were characterized using immunochemical techniques. Antibodies were raised in rabbits to an M_r 58,000 fragment of the transformed (DNA-binding) glucocorticoid receptor purified from rat liver cytosol by DNA-cellulose chromatography and polyacrylamide gel electrophoresis. Antibodies reacted with the transformed receptor form in a radioimmunoassay for glucocorticoid receptor. Western blot analysis of antibody reactivity revealed a single M_r 185,000 receptor form in rat liver cytosol but a smaller M_r 85,000 form in nucleosol, indicating the M_r 85,000 form is the transformed receptor. Furthermore, western blot analysis indicates that the M_r 185,000 receptor undergoes proteolysis during receptor purification and in vitro transformation processes by generating immunochemically similar proteins of smaller molecular weights. An identical M_r 185,000 glucocorticoid receptor was detected in cytosols of four rat tissues; liver, brain, adrenal medulla, and thymus. The glucocorticoid receptor was localized to the cytoplasm and nucleus of rat adrenal medulla cells by immunohistochemistry, demonstrating the existence in vivo of the transformed receptor and translocation of the receptor from cytoplasm to nucleus.     

Oviposition deterring pheromone influences dispersal distance in tephritid fruit flies

We tested the hypothesis that Rhagoletis pomonella females exhibit a greater propensity for engaging in long distance (i.e.1000 m) flight following encounters with egg-infested oviposition-deterring-pheromone (ODP) marked host fruit than similar females that encounter uninfested, clean (i.e. no ODP) fruit. Female flies which were first tethered to flight mills were presented with and permitted to explore (a) ODP-marked or (b) clean fruit and then stimulated to fly. Results showed that females that had encountered a high rate of infested, ODP-marked fruit displayed long distance flight more frequently and flew greater average distances than females that had searched uninfested fruit. We discuss there results in light of contemporary foraging theory.

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Résumé La réponse d'insectes à leurs phéromones de dissuasion (ODP) est examinée généralement à un seul niveau de prospection, c'est-à-dire celui de la ressource individuelle elle-même. Ces marqueurs chimiques peuvent, cependant, fournir aussi des informations au prospecteur sur la disponibilité en ressources, tant au niveau de l'inflorescence qu'au niveau de l'habitat. Une telle information influence vraisemblablement le comportement de prospection à différents niveaux.Dans cette note, nous vérifions l'hypothèse que la rencontre avec des hôtes marqués par ODP influence la tendance de Rhagoletis pomonella (Dipt: Tephrit) à entreprendre des vols importants (c'est-à-dire interhabitats). Nous avons montré dans des expériences de laboratoire que les femelles lors de trois rencontres consécutives avec des fruits marqués par ODP: 1) entreprenaient plus fréquemment (19 cas sur 81 contre 6 sur 81) un vol à longue distance (c'est-à-dire 1000 m) et 2) parcourient des distances moyennes supérieures à celles couvertes par des femelles ayant eu la possibilité de prospecter successivement trois fruits propres (sans ODP).Nous engageons le lecteur à examiner nos résultats d'un point de vue qualitatif. Nous ne pouvons nous attendre à ce qu'un vol à longue distance se produise aussi facilement dans la nature qu'au laboratoire, étant donné le plus grand nombre de variables (par exemple, la taille de l'arbre) qui peuvent y modifier le vol réel.Pour terminer, nous discutons les coûts et bénéfices potentiels qui peuvent résulter de ce comportement.

     

Alteration of arachidonic acid metabolism with spleen microsomes of irradiated rats

Arachidonic acid is metabolized by a rat spleen microsomes cyclooxygenase into prostaglandin D₂, thromboxane B₂, 12-hydroxy-5, 8, 10-heptadecadienoic acid and by a lipoxygenase into 12-hydroxy-5, 8, 10, 14-eicosatetraenoic acid and other unidentified compounds as analyzed by a radiometric thin-layer chromatography method and by gas-chromatography-mass spectrometry. This conversion is modified when spleen microsomes are obtained from whole body irradiated rats. Furthermore, if exogenous cofactors are added to the incubation medium, other changes appear that are different for the lipoxygenase and the cyclooxygenase activities. The results suggest a regulatory role of cofactors on both enzymes and/or a modification of sensitivity of the microsomal fraction from irradiated rats to effectors.     

On the conformational dependence of the proton chemical shifts in nucleosides and nucleotides. II. Proton shifts in the ribose ring of purine nucleosides as a function of the torsion angle about the glycosyl bond

The variations of the ring current, the local diamagnetic susceptibility anisotropy and the polarization contributions to the chemical shift of the non exchangeable protons of the ribose ring of purine nucleosides are computed as a function of the torsion angle about the glycosyl bond, χ_CN. The results show that the ring current effect is relatively more important in the purines than in the pyrimidines. In addition, N₃ of purines has a local magnetic anisotropy effect similar to the one of the carbonyl group C₂O₂ of pyrimidine nucleosides. The experimental differences between the chemical shift of the ribose protons of purine nucleosides and of 8 substituted derivatives are discussed in relation to the theoretical variations.