Redox Intermediates in the Catalase Cycle of Catalase-Peroxidases from <i>Synechocystis</i> PCC 6803<i>, Burkholderia pseudomallei</i>, and <i>Mycobacterium tuberculosis</i>
Bibliographic record
Abstract
Monofunctional catalases (EC 1.11.1.6) and catalase-peroxidases (KatGs, EC 1.11.1.7) have neither sequence nor structural homology, but both catalyze the dismutation of hydrogen peroxide (2H2O2 --> 2H2O + O2). In monofunctional catalases, the catalatic mechanism is well-characterized with conventional compound I [oxoiron(IV) porphyrin pi-cation radical intermediate] being responsible for hydrogen peroxide oxidation. The reaction pathway in KatGs is not as clearly defined, and a comprehensive rapid kinetic and spectral analysis of the reactions of KatGs from three different sources (Synechocystis PCC 6803, Burkholderia pseudomallei, and Mycobacterium tuberculosis) with peroxoacetic acid and hydrogen peroxide has focused on the pathway. Independent of KatG, but dependent on pH, two low-spin forms dominated in the catalase cycle with absorbance maxima at 415, 545, and 580 nm at low pH and 418 and 520 nm at high pH. By contrast, oxidation of KatGs with peroxoacetic acid resulted in intermediates with different spectral features that also differed among the three KatGs. Following the rate of H2O2 degradation by stopped-flow allowed the linking of reaction intermediate species with substrate availability to confirm which species were actually present during the catalase cycle. Possible reaction intermediates involved in H2O2 dismutation by KatG are discussed.
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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) | 0.000 | 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 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".