<sup>18</sup>O Kinetic Isotope Effects Reveal an Associative Transition State for Phosphite Dehydrogenase Catalyzed Phosphoryl Transfer
Bibliographic record
Abstract
Phosphite dehydrogenase (PTDH) catalyzes an unusual phosphoryl transfer reaction in which water displaces a hydride leaving group. Despite extensive effort, it remains unclear whether PTDH catalysis proceeds via an associative or dissociative mechanism. Here, primary 2 H and secondary 18 O kinetic isotope effects (KIEs) were determined and used together with computation to characterize the transition state (TS) catalyzed by a thermostable PTDH (17X-PTDH). The large, normal 18 O KIEs suggest an associative mechanism. Various transition state structures were computed within a model of the enzyme active site and 2 H and 18 O KIEs were predicted to evaluate the accuracy of each TS. This analysis suggests that 17X-PTDH catalyzes an associative process with little leaving group displacement and extensive nucleophilic participation. This tight TS is likely a consequence of the extremely poor leaving group requiring significant P–O bond formation to expel the hydride. This finding contrasts with the dissociative TSs in most phosphoryl transfer reactions from phosphate mono- and diesters.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.004 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".