Transport and Phosphorylation of Xylitol by a Fructose Phosphotransferase System in Streptococcus mutans
Why this work is in the frame
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Bibliographic record
Abstract
The purpose of this work was to explain how the caries-preventive agent xylitol interferes with the growth of Streptococcus mutans. It was found that the xylitol-sensitive strain of S. mutans 27352 (serotype g) and LG1 (serotype c) took up 14C-xylitol when the labelled pentitol was added to cells growing at the expense of glucose. Uptake of xylitol by growing cells of S. mutans 27352 XR and LG1 XR, two xylitol-insensitive spontaneous mutants, and of S. mutans GS5-2, which was also insensitive to xylitol, was practically inexistent under the same conditions. Alkaline phosphatase treatment followed by enzymatic analysis and thin-layer chromatography revealed that the accumulated product was xylitol phosphate. Intracellular concentrations of 5–7 mM for resting cells and of up to 60 mM for growing cells were calculated. Xylitol was phosphorylated at the expense of phosphoenolpyruvate by toluenized cells of S. mutans LG1, but not by toluenized cells of GS5–2 and S. mutans LG1 XR. The phosphorylation of xylitol was dependent on phosphoenolpyruvate and required the presence of both soluble and membrane cellular fractions in the reaction mixture. This indicated that xylitol was transported and phosphorylated by a phosphoenolpyruvate: sugar phosphotransferase system. The phosphoenolpyruvate-dependent phosphorylation by isolated membranes of S. mutans LG1 in the presence of the soluble fraction was inhibited by fructose but not by glucose, mannose or galactose. Measurement of phosphoenolpyruvate: phosphotransferase activities in isolated membrane revealed that strain 27352 and LG1 had activities for fructose and xylitol; membrane from 27352 XR and LG1 XR had very little activity for fructose and xylitol. It was concluded that xylitol was transported and phosphorylated by a constitutive phosphoenolpyruvate:fructose phosphotransferase system in S. mutans. The data suggested that xylitol toxicity in S. mutans is caused by the intracellular accumulation of xylitol phosphate.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it