Bacterial adaptation: Macromolecular biosynthesis during diauxic growth of Escherichia coli

Abstract Synthesis of DNA, RNA and protein was studied during a diauxic adaptation (glucose- to acetate-utilization) of Escherichia coli B. The multiphasic transition described illuminates certain features of the mechanisms regulating metabolism of the 3 macromolecules involved in the genetic flow of information.     

Comparative resistance of Phaseolus vulgaris beans to Callosobruchus chinensis and Acanthoscelides obtectus (Coleoptera: Bruchidae): The differential digestion of soluble heteropolysaccharide

At a concentration of 1 %, a soluble heteropolysaccharide fraction derived from Phaseolus vulgaris beans prevents development of Callosobruchus chinensis but not of Acanthoscelides obtectus. At a concentration of 2 %, it partly inhibits A. obtectus. The differential response could provide a basis for selecting resistant bean varieties. The heteropolysaccharide contains arabinose, xylose, rhamnose, glucose and galactose in approximate molar proportions of 9 : 2 : 1 : 1 : 4. Its biological activity resides mainly in its integral basic structure and only to a small extent in its constituent sugars. The insensitivity of A. obtectus is due to its effectively digesting a large portion of the heteropolysaccharide, releasing most of the contained arabinose, at the larval mid-gut pH of 6.7–6.8. C. chinensis hydrolyses much less of it at its mid-gut pH of 6.4–6.6, whereby the biological activity of the polymer is retained. In vitro digestion of the heteropolysaccharide by A. obtectus enzyme results in a residue which is comparatively inactive on this beetle in vivo, but is still partly toxic for C. chinensis.

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Résumé A la concentration de 1 %, l'extrait de Phaseolus contenant l'heteropolysaccharide soluble, empêche le développement de Callosobruchus chinensis, mais non celui d'Acanthoscelides obtectus. A une concentration de 2 %, il inhibe partiellement ce dernier. Cette différence dans la réponse pourrait servir de base, en vue de la sélection de variétées de pois résistants.L'heteropolysaccharide contient de l'arabinose, du xylose, du rhamnose, du glucose et du galactose dans les proportions respectives approchées en moles 9 : 2 : 1 : 1 : 4. Son activité biologique réside principalement dans l'intégrité de sa structure fondamentale, et seulement à un faible degré dans ses sucres constitutifs. L'insensibilité de Acanthoscelides obtectus est due à ce qu'il digère effectivement une grande portion de l'heteropolysaccharide, libérant la plupart de l'arabinose contenu, cela à PH 6.7–6.8 de l'intestin moyen de la larve, Callosobruchus chinensis en hydrolyse beaucoup moins au PH 6.4–6.6 de son intestin moyen, à la suite de quoi l'activité biologique du polymère est conservée. In vitro la digestion de l'heteropolysaccharide par les enzymes d'Acanthoscelides obtectus engendre un résidu qui est comparativement inactif sur cette espèce in vivo mais est encore partiellement toxique pour Callosobruchus chinensis.

     

Synaptosomal fractions of cat cerebral cortex after hypo-osmotic and detergent treatment.

Different synaptosomal fractions were prepared by subcellular fractionation from cat cerebral cortex. The seperated nerve ending fractions differed in both density and osmotic sensitivity. Synaptosomal ghosts were obtained by hypo-osmotic treatment. In the synaptosomal ghost fractions the synaptic areas seemed to be intact morphologically. The morphology of the "synaptic triad" (pre- and postsynaptic membranes and the synaptic cleft) was not affected even by treatment with Triton X-100 non-ionic detergent (0.6%). The solubilizing effect of different concentrations of the detergent was checked in the supernatants and in the insoluble residues. The homogeneity of various subcellular fractions and the effect of the osmotic and detergent treatments are discussed.     

A combined horseradish peroxidase and Golgi study on the afferent connections of the ventrobasal complex of the thalamus in the cat

Summary Afferent connections to the ventrobasal complex (VB) of the thalamus were studied by means of retrograde transport of horseradish peroxidase (HRP) and by the Golgi-method. After HRP-injection into the VB, peroxidase-positive cells were observed contralaterally in the dorsal column nuclei (DCN), in the trigeminal nuclei and in the lateral cervical nucleus (LCN), and ipsilaterally in the somatosensory I (SI) and II (SII) cortical areas. Labeled cells of different shape and size were compared with neurons impregnated by the Golgi-technique. On the basis of HRP-labeling it is concluded that cells projecting to the VB are different in size and shape even within one region and that they correspond to the relay or efferent neurons observed in the Golgimaterial.     

A theoretical model study of the comparative effectiveness of atropine and scopolamine action in the central nervous system

The molecular structural factors related to the action of atropine and scopolamine at a common biological receptor, with different apparent potencies, are studied from a theoretical viewpoint. The model molecules representing the two cholinergic antagonists are shown to possess the ability to generate an electrostatic potential field which is compatible with the “interaction pharmacophore” of acetylcholine-like molecules. A common site of action for the two types of drugs is rationalized on this basis. The effect of the differences in the molecular structure of the drugs, on their penetration ability and lipid solubility, is analyzed through the proton affinity of model compounds in the gas phase and in solution. These indicate the nature of the stronger solute-solvent interaction of scopolamine. Results from a comparative calculation of the protonation affinity of the solvated drugs are shown to reproduce the correct ratio of protonated versus free base concentrations for the two molecules, from which the reasons for the lower pKa of scopolamine and higher lipophilicity of atropine (free base) can be understood.     

Aym1, a mouse meiotic gene identified by virtue of its ability to activate early meiotic genes in the yeast Saccharomyces cerevisiae

Our understanding of the molecular mechanisms that operate during differentiation of mitotically dividing spermatogonia cells into spermatocytes lags way behind what is known about other differentiating systems. Given the evolutionary conservation of the meiotic process, we screened for mouse proteins that could specifically activate early meiotic promoters in Saccharomyces cerevisiae yeast cells, when fused to the Gal4 activation domain (Gal4AD). Our screen yielded the Aym1 gene that encodes a short peptide of 45 amino acids. We show that a Gal4AD-AYM1 fusion protein activates expression of reporter genes through the promoters of the early meiosis-specific genes IME2 and HOP1, and that this activation is dependent on the DNA-binding protein Ume6. Aym1 is transcribed predominantly in mouse primary spermatocytes and in gonads of female embryos undergoing the corresponding meiotic divisions. Aym1 immunolocalized to nuclei of primary spermatocytes and oocytes and to specific type A spermatogonia cells, suggesting it might play a role in the processes leading to meiotic competence. The potential functional relationship between AYM1 and yeast proteins that regulate expression of early meiotic genes is discussed.     

Carbon Nitride/Reduced Graphene Oxide Film with Enhanced Electron Diffusion Length: An Efficient Photo‐Electrochemical Cell for Hydrogen Generation

Polymeric carbon nitride (CN) has emerged as a promising semiconductor for energy‐related applications. However, its utilization in photo‐electrochemical cells is still very limited owing to poor electron–hole separation efficiency, short electron diffusion length, and low absorption coefficient. Here the synthesis of a highly porous carbon nitride/reduced graphene oxide (CN‐rGO) film with good photo‐electrochemical properties is reported. The CN‐rGO film exhibits long electron diffusion length and high electrochemical active surface area, good charge separation, and enhanced light‐harvesting properties. The film displays a 20‐fold enhancement of photocurrent density over pristine CN, reaching up to 75 µA cm^?2 at 1.23 V versus reversible hydrogen electrode (RHE) in an alkaline solution, as well as stability over a wide pH range. Photocurrent measurements with a hole scavenger reveal a photocurrent density of 660 µA cm^?2 at 1.23 V versus RHE and a quantum efficiency of 60% at 400 nm, resulting in the production of 0.8 mol h^?1 g^?1 of hydrogen. The substantial photo‐electrochemical activity enhancement and hydrogen production together with the low price, high electrochemical surface area, long electron diffusion length, stability under harsh condition, and tunable photophysical properties of CN materials open many possibilities for their utilization in (photo)electrochemical and electronic devices.     

Pyruvate dehydrogenase and glycogen synthase activity at transition from fasted to fed state

The aim of the present study was to evaluate whether the PDC and GS activities at the transition from fasted into fed state are consistent with indirect pathway for glycogen synthesis, as suggested previously. Refeeding of glucose given to rats after 72 hr of starvation did not reactivate PDC in the liver; however, the PDC activity in the muscle was increased. In comparison to PDC, glucose refeeding leads to an opposite effect on GS in both liver and muscle as evidenced by the immediate increase in the active form of GS. The low activity of liver PDC restricts 3-carbon flux through the Krebs cycle and enables their transfer to the gluconeogenic pathway for glycogen synthesis. In contrast, an immediate activation of muscle PDC following refeeding indicates that 3-carbon flux will be oxidized in the citric acid cycle, which thereby eliminates the indirect pathway for glycogen synthesis in this tissue. Glucose infusion increased plasma lactate, insulin, and glycogen content in the liver and muscle to the same extent as observed in the fed rats. The results are in agreement with the suggestion that at the transition from fasted to fed state, liver glycogen synthesis occurs mainly from 3-carbon precursors.     

The influence of processing corn grain on glucose metabolism in ewes.

Glucose metabolism was studied in ewes fed 800 g chopped alfalfa hay (H) or 400 g alfalfa hay and 400 g corn grain given in whole (HWC), ground (HGC) or extruded (HEC) form. Daily intake of metabolisable energy and crude protein were: 5.8 MJ, 109 g; 9.0 MJ, 84 g; 9.5 MJ, 84 g and 8.5 MJ, 88 g in H, HWC, HGC and HEC, respectively. In situ ruminal degradability ranked whole, ground, and extruded corn in ascending order. Ruminal pH and concentration of acetic acid were lower and of propionic acid higher (P less than 0.05) in HEC than in HGC and HWC groups. Plasma level of glucose (P less than 0.10), insulin (P less than 0.05), and the ratio of insulin to non-esterified fatty acids (NEFA) (P less than 0.01) were higher in HEC than in other groups. Glucose irreversible loss (GILR) and entry rate (GER), recycling (GRec) and reentry (GRee) were determined by double isotope dilution procedure. GER, but not GILR, was higher in HWC than in H and HGC (6.98 mg/min/kg BW0.75 vs 3.97 and 4.24 mg/min/kg BW0.75, respectively; P less than 0.05) and than in HEC (4.84 mg/min/kg BW0.75; P less than 0.10). GRec and GRee were higher in HWC than in the other treatments. Grinding or extruding the grain increased ruminal degradability and decreased glucose entry rate.