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The effect of adding SiO$\_2$ to a precipitated Fe-based Fischer–Tropsch catalyst was investigated. Silica was added to the catalyst either during or after precipitation. The iron-based Fischer–Tropsch catalysts were studied using Mössbauer spectroscopy, BET surface area, XRD and SEM characterization methods. Adding SiO$\_2$ to the catalyst during precipitation or immediately after precipitation (i.e., precipitated SiO$\_2$) results in the formation of Fe crystallites with an average diameter less than 3 nm, which have high surface areas and exhibit a strong interaction with the SiO$\_2$ matrix. Consequently, these crystallites are resistant to reduction and carburisation. When SiO$\_2$ was added to the catalyst after heat treatment (i.e., binder SiO$\_2$), the resulting catalyst was observed to consist of segregated SiO$\_2$-rich and Fe-rich phases. The distribution of K$\_2$O in both these phases indicates that the amount of effective K$\_2$O, i.e., that associated with Fe, is less when SiO$\_2$ is added as a binder. The low extent of reduction and carburisation observed with catalysts that contain precipitated SiO$\_2$ results in catalysts with low % CO conversion. A positive correlation between the amount of iron carbides present in the catalyst and the % CO conversion was observed in these studies.

β-Aspartylglycine can adequately be used as an indicator of colonisation-resistance as its presence reflects the absence of β-aspartylpeptide-degrading activity originating from a substantial number of different strains of anaerobic bacteria. In this study, 14 strains of anaerobic bacteria were isolated from human faeces and the β-aspartyl-peptide-degrading activity in these bacteria was determined by a high-performance liquid chromatography assay. In 12 of 14 strains this activity was present, which indicates that its absence indeed reflects a substantial disturbance of the anaerobic bacterial flora. In addition, the assay was used to determine β-aspartylpeptidase activity in faecal supernatants of healthy volunteers and decontaminated patients.

In the current study, the hypothesis that thermal radiosensitization is (indirectly) caused by heat-induced denaturation and aggregation of nuclear proteins is further investigated. Thermotolerant rodent cells showed a reduced intranuclear protein aggregation as compared with non-tolerant cells immediately after a heat treatment. This was reflected in the extent of radiosensitization when the cells were X-irradiated immediately after a heat treatment. When heat and radiation were separated in time, a faster disaggregation was found in thermotolerant cells, which was paralleled by a more rapid decline of radiosensitization. Cells transfected with hsp72 showed protection against heat-induced nuclear protein aggregation and reduced thermal radiosensitization. Transfection with hsp27 resulted in an accelerated nuclear protein disaggregation and accelerated decline of thermal radiosensitization. Despite a significant overall correlation between TER and nuclear protein aggregation, the slopes of the correlation curves for the individual cell lines deviated significantly. Yet, the experiments support the hypothesis that radiosensitization is primarily caused by inhibition of DNA repair as a result of the presence of denatured and aggregated proteins in the cell nucleus. Expression of hsps (e.g. in thermotolerant cells), by affecting nuclear protein aggregation, can have an impact on thermal radiosensitization.

The stress proteins hsp25 αB-crystallin are found in increased concentrations in reactive astrocytes of brains undergoing neurodegeneration. In order to characterize this reaction, we investigated the expression of hsp25 and αB-crystallin during growth and after stress (heat shock) in glial cells in vitro. In primary rat brain cultures, hsp25 was present in actively dividing astrocytes that were positive for glial fibrillary acidic protein. αB-crystallin was found predominantly in oligodendrocytes. Heat shock resulted in increased concentrations of hsp25 and αB-crystallin in astrocytes, without any detectable changes in intracellular localization, as detectable with confocal laser microscopy. These results indicate that a neurodegeneration-related increase of the small stress proteins in astrocytes is independent of gliosis per se, and may be a disease-related event.

Heat treatment of cells results in an increased protein content of nuclei and nuclear matrices when isolated after the heat treatment. This increase of TX-100 insoluble protein is interpreted as being the result of protein denaturation and subsequent aggregation. After the heat treatment cells can (partly) recover from these aggregates. Recent data suggest that heat shock proteins (hsps) might be involved in the recovery (disaggregation) from these heat-induced insoluble protein complexes. In this report, the role of hsp72 in the process of aggregation and disaggregation was investigated using: non-tolerant rat-1 cells, thermotolerant rat-1 cells (rat-1 TT), and transfected rat-1 cells constitutively expressing the human inducible hsp72 gene (HR-24 cells). After heating the various cells, it was observed that the expression of the human hsp72 confers heat resistance (43-45°C). Heat-induced intranuclear protein aggregation was less in HR and rat-1 TT cells as compared to nontolerant rat-1 cells. After heat treatments leading to the same initial intranuclear protein aggregation, rat-1 TT cells recovered more rapidly from these aggregates, while HR cells recovered at the same rate as nontolerant rat-1 cells. Our data suggest that increased levels of hsp72 can confer heat resistance at the level of initial (nuclear) heat damage. Elevated levels of hsp72 alone, however, do not enable cells to recover more rapidly from heat-induced intranuclear protein aggregates.