Pancreatic hepatocytes in hamsters (Mesocricetus auratus) infected with Trypanosoma cruzi

Hepatocytic metaplasia may be induced in hamsters by carcinogens, and associated with aging, diabetes or chronic pancreatitis. By means of histopathologic and immunohistochemic studies, we observed pancreatic hepatocytes in hamsters infected and reinfected with Trypanosoma cruzi. The change was seen in 18 (19%) out of 94 infected animals, and was not found among 53 controls, Normal islet cells were immunoreactive for neuron-specific enolase and not reactive for NCL-HAS. Metaplastic cells were immunoreactive for NCL-HAS and not reactive for islet hormones and enolase. No relationship was observed between number of inoculations and metaplasia; however, the intensity of the inflammatory process and sequels seems to favor the development of metaplastic cells. Hamsters infected with T. cruzi may be useful to study hepatocytic metaplasia, and contribute to clarify aspects of Chagas' disease and pancreatic changes. Our data indicate that aging, in addition to inflammation and atrophy, plays a role in this change.     

Induction and stimulation of in vitro flowering of Pharbitis nil by cytokinin and gibberellin

The influence of BA, GA₃ and IAA applied successively onflower bud formation in shoot apices of Pharbitis nil hasbeen investigated. The shoot apices were isolated from seedlings cultivatedunder non-inductive continuous light and from seedlings exposed to asubinductive (12 h) dark period. BA and GA₃ introducedsuccessively into culture medium replaced the inductive night, causing theflowering of plantlets in completely non-inductive continuous light (optimalconcentration of BA – 10^–7–10^–6mol dm^–3, GA₃ –10^–7–10^–6 moldm^–3) and stimulated this process under thesubthresholdinduction. These hormones applied in reverse sequence (in the first placeGA₃, then BA) did not affect flowering of explants. IAA nullifiedthestimulating effect of BA and GA₃. The influence of phytohormones onflowering may result from the change of growth correlations within the shootapical meristem.     

On the mechanism of interaction of organic solvents with the active site of alpha-chymotrypsin

Kinetic behavior of -chymotrypsin in the reaction of hydrolysis of the N-acetyl-L-tyrosine derivatives was investigated in non-denaturing water–dimethylsulfoxide and water–ethanol mixtures. Similar specific interactions between the two solvents and the active site of -chymotrypsin were shown to result in similar kinetic effects. It is proposed that the changes in the active site structure of the enzyme caused by the interaction with the organic solvents (conformational isomer formation) resulted in two parallel processes—acceleration of the acyl-enzyme formation step and a decrease in the deacylation rate. The possible molecular mechanism of this phenomenon and an adequate kinetic model describing the data are discussed.     

Talisia esculenta lectin and larval development of Callosobruchus maculatus and Zabrotes subfasciatus (Coleoptera: Bruchidae)

Bruchid larvae cause major losses in grain legume crops throughout the world. Some bruchid species, such as the cowpea weevil and the Mexican bean weevil, are pests that damage stored seeds. Plant lectins have been implicated as antibiosis factors against insects, particularly the cowpea weevil, Callosobruchus maculatus. Talisia esculenta lectin (TEL) was tested for anti-insect activity against C. maculatus and Zabrotes subfasciatus larvae. TEL produced ca. 90% mortality to these bruchids when incorporated in an artificial diet at a level of 2% (w/w). The LD(50) and ED(50) for TEL was ca. 1% (w/w) for both insects. TEL was not digested by midgut preparations of C. maculatus and Z. subfasciatus. The transformation of the genes coding for this lectin could be useful in the development of insect resistance in important agricultural crops.     

The novel non-glycosylated invertase from Candida utilis (the properties and the conditions of production and purification)

The Candida utilis yeast, which is cultivated in liquid media enriched with saccharose, synthesizes the well-known invertase of 300 kDa (EC 3.2.1.26). This enzyme is present both intracellularly in the periplasmic space and extracellularly in the culture broth. However, it was determined that the same C. utilis strain cultured in certain conditions is simultaneously capable of producing another, still unknown form of invertase with a molecular mass of 60 kDa. The presence of the latter enzymatic form was detected in cells as well as in the liquid culture medium. Both invertase forms were purified using a three-step process (ion-exchange chromatography, affinity chromatography, and preparative column electrophoresis) and named, due to their different migration ratio in polyacrylamide gel electrophoresis, F-form (Fast; 60 kDa) and S-form (Slow; 300 kDa). The F-form of invertase was found to be nonglycosylated as opposed to the well-known S-form of invertase from the same source. The physicochemical properties of the F-form of invertase (isoelectric point, substrate specificity, pH, and temperature optima) were determined and compared with those of the S-form of the enzyme.     

Munc13-4 is essential for cytolytic granules fusion and is mutated in a form of familial hemophagocytic lymphohistiocytosis (FHL3)

Secretion of cytolytic granules content at the immunological synapse is a highly regulated process essential for lymphocyte cytotoxicity. This process requires the rapid transfer of perforin containing lytic granules to the target cell interface, followed by their docking and fusion with the plasma membrane. Defective cytotoxicity characterizes a genetically heterogeneous condition named familial hemophagocytic lymphohistiocytosis (FHL), which can be associated with perforin deficiency. The locus of a perforin (+) FHL subtype (FHL3), observed in 10 patients, was mapped to 17q25. This region contains hMunc13-4, a member of the Munc13 family of proteins involved in vesicle priming function. HMunc13-4 mutations were shown to cause FHL3. HMunc13-4 deficiency results in defective cytolytic granule exocytosis, despite polarization of the secretory granules and docking with the plasma membrane. Expressed tagged hMunc13-4 localizes with cytotoxic granules at the immunological synapse. HMunc13-4 is therefore essential for the priming step of cytolytic granules secretion preceding vesicle membrane fusion.     

Membrane fluidity adjustments in ethanol-stressed Oenococcus oeni cells

The effect of ethanol on the cytoplasmic membrane of Oenococcus oeni cells and the role of membrane changes in the acquired tolerance to ethanol were investigated. Membrane tolerance to ethanol was defined as the resistance to ethanol-induced leakage of preloaded carboxyfluorescein (cF) from cells. To probe the fluidity of the cytoplasmic membrane, intact cells were labeled with doxyl-stearic acids and analyzed by electron spin resonance spectroscopy. Although the effect of ethanol was noticeable across the width of the membrane, we focused on fluidity changes at the lipid-water interface. Fluidity increased with increasing concentrations of ethanol. Cells responded to growth in the presence of 8% (vol/vol) ethanol by decreasing fluidity. Upon exposure to a range of ethanol concentrations, these adapted cells had reduced fluidity and cF leakage compared with cells grown in the absence of ethanol. Analysis of the membrane composition revealed an increase in the degree of fatty acid unsaturation and a decrease in the total amount of lipids in the cells grown in the presence of 8% (vol/vol) ethanol. Preexposure for 2 h to 12% (vol/vol) ethanol also reduced membrane fluidity and cF leakage. This short-term adaptation was not prevented in the presence of chloramphenicol, suggesting that de novo protein synthesis was not involved. We found a strong correlation between fluidity and cF leakage for all treatments and alcohol concentrations tested. We propose that the protective effect of growth in the presence of ethanol is, to a large extent, based on modification of the physicochemical state of the membrane, i.e., cells adjust their membrane permeability by decreasing fluidity at the lipid-water interface.