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Biomedical subjects

S Kneist

Publications and source records attributed to S Kneist.

42 records · Page 3Linked to original sources
PubMed1979

Activity of citrinin metabolized by rat and human microsome fractions in clastogenicity and SCE assays on Chinese hamster V79-E cells.

The mycotoxin citrinin is a potent inducer of chromosomal aberrations in the clastogenicity assay on V79-E cells when metabolized by rat and human liver microsomes. Rat and human liver microsomes, standardized on protein content, activate citrinin at equal levels. 5 X 10(-4) M citrinin induces complex translocations in a high frequency as well as defects of chromosomal coiling. Higher concentrations are cytotoxic, lower ones are almost inactive. After metabolization of mycotoxin by rat-kidney microsomes or an S9 mix fraction containing rat liver and kidney microsomes, toxic effects predominate and chromosomal aberrations are diminished. Clastogenic citrinin concentrations do not induce an increase of SCE frequency. Although the mode of action of this mycotoxin on chromosomal structure remains obscure, possible explanations are discussed.

Animals↗
PubMedDate not supplied

Differences in acidogenicity of S. sobrinus and S. rattus are linked to the catalytic efficiency of the glycolytic key enzyme phosphofructokinase.

This contribution describes the biochemical properties of two catalytically different phosphofructokinases (PFKs) purified from Streptococcus rattus LB 2 (PFK-rat) and Streptococcus sobrinus OMZ 65 (PFK-sob), respectively. Steady-state kinetics revealed K(M) = 0. 8 mM for PFK-rat and K(M) = 0.08 mM for PFK-sob for F-6-P as the substrate. The enzymes also differ in their pH profiles: whereas the highest activity of PFK-rat was measured at pH = 8.0, the optimum pH of PFK-sob was at pH = 7.0. In addition, compared to PFK-sob, PFK-rat was more sensitive against the allosteric inhibitor ATP. PFK catalyzes a committed step of glycolysis, the main acid producing catabolic pathway. Thus, the catalytically more efficient enzyme isolated from S. sobrinus OMZ 65, especially at low pH, could explain the comparably high acidogenicity of this strain.

Bacterial Proteins↗
PubMedDate not supplied

Peroxidase reaction as a parameter for discrimination of Streptococcus mutans and Streptococcus sobrinus.

425 strains of mutans streptococci and 12 reference strains were investigated by membrane fatty acid spectra (MFAS) and peroxidase reaction (PR) after aerobic and anaerobic incubation. 423 strains were identified as Streptococcus mutans. The remaining 2 strains were identified as Streptococcus sobrinus. The PR of 29 strains was doubtful; immediately after anaerobic incubation a negative PR changed into a slightly positive PR. To test the diagnostic value of PR the strains were additionally investigated by means of species-specific polymerase chain reactions (PCR). The species-specific PCRs were developed on the basis of the respective genes of 16S rRNA of the pathogens S. mutans and S. sobrinus. Specificity and sensitivity were tested on reference strains (n = 17) and negative control strains (n = 39). The results of this investigation showed that an anaerobic incubation regime could lead to false-positive (S. mutans) or false-negative (S. sobrinus) PR. The 425 MS strains were classified as either S. mutans (n = 420) or S. sobrinus (n = 5). The findings on the reference strains required a reclassification of S. mutans V 100 into S. sobrinus V 100. Summarising, it is possible now to differentiate strains of mutans streptococci by MFAS and PR after aerobic incubation.

Aerobiosis↗