Catalytic Differences between Flavohemoglobins of Giardia intestinalis and E. coli
Notice bibliographique
Résumé
The sole known heme enzyme of the parasitic protist Giardia intestinalis is a flavohemoglobin (gFlHb) that acts as a nitric oxide dioxygenase (NOD) and protects the organism from the free radical nitric oxide. To learn more about the properties of this enzyme, we measured its nitric oxide dioxygenase, NADH oxidase, and cytochrome c reductase activities and compared these to the activities of the E. coli flavohemoglobin (Hmp). The turnover number for the NOD activity of gFlHb (23 s−1) is about two-thirds of that of Hmp (34 s−1) at pH 6.5 and 37 °C. The two enzymes differ in their sensitivity towards molecules that act as heme ligands. For both gFlHb and Hmp, inhibition with miconazole, a large imidazole ligand, is adequately described by simple competitive inhibition, with KI = 10 μM and 0.27 μM for gFlHb and Hmp, respectively. Inhibition plots with the small ligand imidazole were biphasic, which is consistent with previous experiments with carbon monoxide as a probe that show that the active site of flavohemoglobins exists in two conformations. Interestingly, the largest difference is observed with nitrite, which, like imidazole, also shows a biphasic inhibition plot; however, nitrite inhibits gFlHb at sub-millimolar concentrations while Hmp is not significantly affected. NADH oxidase activity measured under aerobic conditions in the absence of nitric oxide for Hmp was more than twice the activity of gFlHb. The addition of 1 mM hydrogen peroxide in these assays stimulated the NADH oxidase activity of gFlHb but not Hmp. Both enzymes had nearly identical cytochrome c reductase activities but the extent of the contribution of indirect reduction by flavohemoglobin-generated superoxide was much lower with gFlHb (4% SOD-inhibited) than with Hmp (17% SOD-inhibited). Although the active sites of the two enzymes share the same highly conserved residues that are important for catalysis, differences in the distal ligand binding site may account for these differences in activity and sensitivity towards NOD inhibitors. The differences observed in the NADH oxidase and cytochrome c reductase assays suggest that gFlHb may have evolved to protect the protist, which lacks both superoxide dismutase and catalase, from the damaging effects of superoxide by minimizing its production and from peroxide by actively reducing it.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».