Molecular forms of acetylcholinesterase present in the white and grey matter of pig brain

Extraction of the white matter of pig brain with EDTA, lysolecithin or Triton X-100 gave poor yields of soluble acetylcholinesterase although these agents had proved effective at solubilizing the enzyme in the grey matter. This finding, together with the observation that the strong detergent sodium deoxycholate, was needed to solubilize the enzyme, shows that it is more difficult to remove acetylcholinesterase from the white matter of brain than from the grey. This could mean that the enzyme in the white matter is more firmly bound to the membrane than the enzyme in the grey matter.The difference in binding of the enzyme from the two regions of the brain is also reflected in the affinity chromatography experiments which showed a lower recovery for the acetylcholinesterase of white matter compared with the enzyme from grey matter.Starch-block electrophoresis of acetylcholinesterase showed a single negatively charged peak of activity for both the naturally soluble and the deoxycholate solubilized preparations. The presence of only one form on electrophoresis suggests that the molecular species of acetylcholinesterase do not arise from differences in charge.Sucrose density gradient centrifugation of the two preparations from white matter gave a single peak of activity with a sedimentation constant of about 10 S. This corresponds closely to the major species of molecular weight 260,000 detected by gradient gel electrophoresis. Other forms detected in both enzyme preparations by gradient gel electrophoresis were species with molecular weights of 660,000, 180,000, 130,000 and 115,000. The significance of these species in terms of the formation of oligomers is discussed.A comparison was made with the corresponding preparations of acetylcholinesterase from the grey matter and the results showed that acetylcholinesterase from the white and grey matter of pig brain were very similar. The exception to this was the species with a molecular weight of 68,000 which was present in the grey but not the white matter of pig brain.     

Interaction of mannose-6-phosphate with the hysteretic transition in glucose-6-phosphate hydrolysis in intact liver microsomes.

We showed previously that glucose-6-phosphatase activity was characterised in intact liver microsomes by a hysteretic transition between a rapid and a slower catalytic form of the enzyme. We have now further investigated the substrate specificity of these two kinetic forms. It was found that the pre-incubation of intact microsomes with mannose-6-phosphate or glucose-6-phosphate (50 microM for 30 s) suppressed the burst in glucose-6-phosphatase activity, that the hysteretic transition was reversible and that mannose-6-phosphate inhibited glucose-6-phosphate hydrolysis during the first seconds of incubation, but not anymore after the burst. Our results indicate (i) that mannose-6-phosphate is recognised by the enzyme and can promote the hysteretic transition and (ii) that the transient phase is part of the catalytic mechanism itself.     

Effect of methabenzthiazuron on growth and nitrogenase activity in Vicia faba

The effects of the herbicide methabenzthiazuron (175 and 220 g ha^-1) on vegetative and reproductive growth, nodulation and nitrogenase activity of Vicia faba were studied in the field under Mediterranean conditions. Nitrogenase activity of excised nodules was estimated using the acetylene reduction assay four times during the developmental period. Leaf area index, dry weight and nitrogen content of the different parts of the plants were measured. Methabenzthiazuron-treated plants showed an increase in nodulation, nitrogenase activity and vegetative growth at early pod fill. Methabenzthiazuron also caused an increase in leaf N content and fruits. These were transient effects found during early and mid pot fill. Nevertheless, plants treated with these sublethal doses of herbicide improved seed production and nitrogen content of seeds at harvest time. The stimulatory effect of methabenzthiazuron on N₂ fixation and vegetative growth seems not be related with the transient stimulatory effect on photosynthetic capacity, also caused by the herbicide, since the stimulatory effect on N₂ fixation was apparent during pod fill, when photosynthetic capacity declined and was not modified by methabenzthiazuron.     

Demonstration of the capacity of nacre to induce bone formation by human osteoblasts maintained in vitro.

Nacre implanted in vivo in bone is osteogenic suggesting that it may possess factor(s) which stimulate bone formation. The present study was undertaken to test the hypothesis that nacre can induce mineralization by human osteoblasts in vitro. Nacre chips were placed on a layer of first passage human osteoblasts. None of the chemical inducers generally required to obtain bone formation in vitro was added to the cultures. Osteoblasts proliferated and were clearly attracted by nacre chips to which they attached. Induction of mineralization appeared preferentially in bundles of osteoblasts surrounding the nacre chips. Three-dimensional nodules were formed by a dense osteoid matrix with cuboidal osteoblasts at the periphery and osteocytic-like cells in the center. These nodules contained foci with features of mineralized structures and bone-like structures, both radiodense to X-ray. Active osteoblasts (e.m.) with abundant rough endoplasmic reticulum, extrusion of collagen fibrils and budding of vesicles were observed. Matrix vesicles induced mineral deposition. Extracellular collagen fibrils appeared cross-banded and electrodense indicating mineralization. These results demonstrate that a complete sequence of bone formation is reproduced when human osteoblasts are cultured in the presence of nacre. This model provides a new approach to study the steps of osteoblastic differentiation and the mechanisms of induction of mineralization.     

Assay of β-galactosidase activity by Flow Injection Analysis (FIA)

Summary A novel method to analyze -galactosidase by Flow Injection Analysis is presented with a linear working range extended to at least 2150 U/mL, being the detection limit 25 U/mL with 55 samples per hour frecuency and a BSD of 0.954% versus 2.4% obtained by manual assay. The method was tested with optimal results with samples from Escherichia coli cultures producing -galactosidase.     

Direct Selection for Mutants with Increased K(+) Transport in Saccharomyces Cerevisiae

Saccharomyces cerevisiae cells containing a deletion of TRK1, the gene encoding the high affinity potassium transporter, retain only low affinity uptake of this ion and consequently lose the ability to grow in media containing low levels (0.2 mM) of potassium. Using a trk1 delta strain, we selected spontaneous Trk+ pseudorevertants that regained the ability to grow on low concentrations of potassium. The revertants define three unlinked extragenic suppressors of trk1 delta. Dominant RPD2 mutations and recessive rpd1 and rpd3 mutations confer increased potassium uptake in trk1 delta cells. Genetic evidence suggests that RPD2 mutations are alleles of TRK2, the putative low affinity transporter gene, whereas rpd1 and rpd3 mutations increase TRK2 activity: (1) RPD2 mutations are closely linked to trk2, and (2) trk2 mutations are epistatic to both rpd1 and rpd3. rpd1 maps near pho80 on chromosome XV and rpd3 maps on the left arm of chromosome XIV, closely linked to kre1.     

Drought tolerance processes in soybeans

Fifteen soybean cultivars were evaluated in two water supply conditions, inducing or not a drought stress. Main canopy traits were measured several times during the reproductive period and, at maturity date, the yield components were estimated. Using principal components analysis, the main physiological functions involved in soybean drought tolerance are described: leaf cells enlargement and assimilates transport. These processes could be a good basis on which to define new selection criteria for soybean drought tolerance.     

The effect of clupeinon anisotropy and basophilia of polytene chromosomes

Summary When polytene chromosomes are subjected to a clupein treatment, their properties of basophilia and anisotropy are affected. The basophilia is deeply reduced, except in the nucleolar zones, puffs and sites of RNA accumulation. On the other hand, the chromosome birefringence increases. The phenomenon of anomalous dispersion of birefringence usually observed on polytene chromosomes stained with toluidine blue solutions turns into a normal negative dispersion of birefringence, when staining is preceded by clupein treatment. It is concluded that the clupein molecules attach orderly and preferentially to sequential DNA phosphates unbound to chromosome proteins, accentuating DNA anisotropic characteristics. The clupein molecules appear not attaching to RNA phosphates.     

Vegetative innervation of the esophagus. II. Intraganglionic laminar endings.

The intraganglionic laminar endings in the esophagus of the cat and the rhesus monkey show absolute equivalence between the results in both species from the morphological standpoint. The different types of apparatus found are described, with their location in the esophagus and their percentage distribution in relation to the different portions of its wall. The osmium tetroxide-zinc iodide technique gives pictures equivalent to those using silver impregnations, with the added advantage that the former brings out the morphological details more clearly, to the point of showing up the peculiar characteristics of the edges with their thorn-like protrusions. The complete independence of these structures within the ganglion is confirmed, and evidence is provided for rejecting the possibility that they might be dendritic prolongations of the neuronal elements composing the intramural ganglia. A possible afferent function is proposed, which, however, must be considered an open question, pending the results of further experimental investigation.