Mutational study of the role of tyrosine‐49 in the <i>Saccharomyces cerevisiae</i> xylose reductase
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Bibliographic record
Abstract
The xyl1 gene encoding xylose reductase was cloned from Saccharomyces cerevisiae and expressed in Escherichia coli. The purified enzyme readily carried out xylose reduction in vitro. It prefers NADPH as the co-enzyme by about 80-fold over NADH. Compared to the native enzyme purified from S. cerevisiae (Kuhn et al., 1995), the recombinant xylose reductase displayed slightly higher (about two-fold) affinities (K(m)) for the substrate (xylose) and co-factor (NADPH), as well as a 3.9-fold faster turnover number (K(cat)) and 7.4-fold greater catalytic efficiency (K(cat)/K(m)). The reason for the apparent discrepancies in kinetic constants between the recombinant and native S. cerevisiae xylose reductases is not known. Replacement of Tyr49 by Phe in the recombinant enzyme led to greater than 98% loss of activity, suggesting that this residue plays a critical role in catalysis. Intrinsic enzyme fluorescence spectroscopic analysis showed that the wild-type and the Y49F variant both bound the co-enzyme NADPH with similar affinity. This supports the view that Tyr49 is involved in interaction with the substrate and not the co-factor during catalysis.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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