Modulation of the Activities of Catalase−Peroxidase HPI of <i>Escherichia coli</i> by Site-Directed Mutagenesis
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Bibliographic record
Abstract
Catalase-peroxidases have a predominant catalatic activity but differ from monofunctional catalases in exhibiting a substantial peroxidatic reaction which has been implicated in the activation of the antitubercular drug isoniazid in Mycobacterium tuberculosis. Hydroperoxidase I of Escherichia coli encoded by katG is a catalase-peroxidase, and residues in its putative active site have been the target of a site directed-mutagenesis study. Variants of residues R102 and H106, on the distal side of the heme, and H267, the proximal side ligand, were constructed, all of which substantially reduced the catalatic activity and, to a lesser extent, the peroxidatic activity. In addition, the heme content of the variants was reduced relative to the wild-type enzyme. The relative ease of heme loss from HPI and a mixture of tetrameric enzymes with 2, 3, and 4 hemes was revealed by mass spectrometry analysis. Conversion of W105 to either an aromatic (F) or aliphatic (I) residue caused a 4-5-fold increase in peroxidatic activity, coupled with a >99% inhibition of catalatic activity. The peroxidatic-to-catalatic ratio of the W105F variant was increased 2800-fold such that compound I could be identified by both electronic and EPR spectroscopy as being similar to the porphyrin cation radical formed in other catalases and peroxidases. Compound I, when generated by a single addition of H(2)O(2), decayed back to the native or resting state within 1 min. When H(2)O(2) was generated enzymatically in situ at low levels, active compound I was evident for up to 2 h. However, such prolonged treatment resulted in conversion of compound I to a reversibly inactivated and, eventually, to an irreversibly inactivated species, both of which were spectrally similar to compound I.
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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) | 0.001 | 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