Lysozyme inactivation and aggregation in stirred-reactor

Mechanisms of enzyme inactivation and aggregation are still poorly understood. In this work, we are considering the characterisation of both inactivation and aggregation in stirred tank reactor, with lysozyme as the model enzyme.

The inactivation kinetics are first order. For stirring speeds in the range of 0–700 rpm, the kinetic constant is found to be proportional to the power brought by the impeller. It suggests that inactivation depends on collisions between enzyme molecules. Efficient collisions between native and inactive molecules induce native molecules to turn into inactive molecules and lead to lysozyme aggregation.

During inactivation, enzymes are found to aggregate as shown by light scattering measurements. The structure of aggregates was studied on samples treated for chemical denaturation and reduction. The aggregates are supramolecular edifices, mainly made up of inactivated enzymes linked by weak forces. But aggregates are also made up of dimers and trimers of lysozyme, linked by disulfide bridges. Dimers and trimers are 18% and 5%, respectively, of the total amount of lysozyme aggregates.

Whatever the stage of aggregate formation and the initial enzyme concentration are, these aggregates are irreversibly inactivated. Enzyme activity is definitely lost even if stirring is stopped and/or temperature decreased.

This study points out the importance of hydrodynamics in bioreactors and highlights the nature of the aggregates resulting from the interactions between native and inactive enzymes.     

Assessment of interleukin 1 and interleukin 2 effects on cycling and noncycling murine thymocytes

When mouse thymocytes are stimulated with PHA, the proliferative response is very low, unless the culture medium is enriched with interleukin 1 (IL-1)- or interleukin 2 (IL-2)-containing supernatants. Cytofluorometric analyses show, however, that PHA stimulation generates a significant number of cells with increased RNA content (transition from the G₀ to G₁ phase of the cell cycle). If IL-2 is added to such cultures, the activated cells complete their process of RNA synthesis and then enter the S phase. The use of IL-2-containing culture medium thus permits one to obtain a high correlation between the number of g₁ cells and [³H]thymidine incorporation (r = 0.97). Enrichment with IL-1-containing supernatants also results in a statistically significant correlation (r = 0.68), but the regression lines are markedly different for the two interleukins (s = 20.3 for IL-2 and s = 9.2 for IL-1), when analyzed after 48 hr of incubation. These observations suggest that the G₁ phase must be divided into two subcompartments, G_1a and G_1b, the G_1a-G_1b transition being an IL-2-dependent event. If the number of G_1b cells is used to establish correlations with [³H]thymidine incorporation, all values fall on the same regression line, regardless of culture conditions and of the addition of interleukins. It is concluded that IL-2 regulates lymphocyte proliferation at the level of RNA synthesis (G_1a-G_1b transition) rather than that of DNA synthesis (G₁-S transition).     

Identification and characterization of adhesive factors of Clostridium difficile involved in adhesion to human colonic enterocyte-like Caco-2 and mucus-secreting HT29 cells in culture

Experiments reported in this communication showed that the highly toxinogenic Cd 79685, Cd 4784, and Wilkins Clostridium difficile strains and the moderately toxinogenic FD strain grown in the presence of blood adhere to polarized monolayers of two cultured human intestinal cell lines: the human colonic epithelial Caco-2 cells and the human mucus-secreting HT29-MTX cells. Scanning electron microscopy revealed that the bacteria interacted with well-defined apical microvilli of differentiated Caco-2 cells and that the bacteria strongly bind to the mucus layer that entirely covers the surface of the HT29-MTX cells. The binding of C. difficile to Caco-2 cells developed in parallel with the differentiation features of the Caco-2 cells, suggesting that the protein(s) which constitute C. difficile-binding sites are differentiation-related brush border protein(s). To better define this interaction, we tentatively characterized the mechanism(s) of adhesion of C. difficile with adherence assays. It was shown that heating of C. difficile grown in the presence of blood enhanced the bacterial interaction with the brush border of the enterocyte-like Caco-2 cells and the human mucus-secreting HT29-MTX cells. A labile surface-associated component was involved in C. difficile adhesion since washes of C. difficile grown in the presence of blood without heat shock decreased adhesion. After heating, washes of C. difficile grown in the presence of blood did not modify adhesion. Analysis of surface-associated proteins of C. difficile subjected to different culture conditions was con-ducted. After growth of C. difficile Cd 79685, Cd 4784, FD and Wilkins strains in the presence of blood and heating, two predominant SDS-extractable proteins with molecular masses of 12 and 27 kDa were observed and two other proteins with masses of 48 and 31 kDa disappeared. Direct involvement of the 12 and 27 kDa surface-associated proteins in the adhe-sion of C. difficile strains was demonstrated by using rat polycolonal antibodies pAb 12 and pAb 27 directed against the 12 and 27kDa proteins. Indeed, adhesion to Caco-2 cell monoiayers of C. difficiie strains grown in the presence of blood, without or with heat-shock, was blocked. Taken together, our results suggest that C. difficiie may utilize blood components as adhesins to adhere to human intestinal cultured cells.     

Antibacterial activity against β- lactamase producing Methicillin and Ampicillin-resistants Staphylococcus aureus: fractional Inhibitory Concentration Index (FICI) determination

Background

The present study reports the antibacterial capacity of alkaloid compounds in combination with Methicillin and Ampicillin-resistants bacteria isolated from clinical samples. The resistance of different bacteria strains to the current antibacterial agents, their toxicity and the cost of the treatment have led to the development of natural products against the bacteria resistant infections when applied in combination with conventional antimicrobial drugs.

Method

The antibacterial assays in this study were performed by using inhibition zone diameters, MIC, MBC methods, the time-kill assay and the Fractional Inhibitory Concentration Index (FICI) determination. On the whole, fifteen Gram-positive bacterial strains (MRSA/ARSA) were used. Negative control was prepared using discs impregnated with 10 % DMSO in water and commercially available Methicillin and Ampicillin from Alkom Laboratories LTD were used as positive reference standards for all bacterial strains.

Results

We noticed that the highest activities were founded with the combination of alkaloid compounds and conventional antibiotics against all bacteria strains. Then, results showed that after 7 h exposition there was no viable microorganism in the initial inoculums.

Conclusion

The results of this study showed that alkaloid compounds in combination with conventional antibiotics (Methicillin, Ampicillin) exhibited antimicrobial effects against microorganisms tested. These results validate the ethno-botanical use of Cienfuegosia digitata Cav. (Malvaceae) in Burkina Faso. Moreover, this study demonstrates the potential of this herbaceous as a source of antibacterial agent that could be effectively used for future health care purposes.     

SynTReN: a generator of synthetic gene expression data for design and analysis of structure learning algorithms

Background  

The development of algorithms to infer the structure of gene regulatory networks based on expression data is an important subject in bioinformatics research. Validation of these algorithms requires benchmark data sets for which the underlying network is known. Since experimental data sets of the appropriate size and design are usually not available, there is a clear need to generate well-characterized synthetic data sets that allow thorough testing of learning algorithms in a fast and reproducible manner.     

Species variations amongst proteinases in liver lysosomes

Cathepsin B, H, L and D activities in liver lysosomes were compared between species. Although cathepsin B and D were detected in bovine, pig, chicken and rat liver, striking species differences were evident for cathepsin H and L. Cathepsin L activity was particularly high in chicken lysosomal extracts, but could not be detected in bovine and pig extracts. Whereas there was no significant cathepsin H activity in bovine extracts, rat liver lysosomal extracts contained large amounts of cathepsin H activity.