Understanding the Factor Va Cofactor Effect within Prothrombinase.
Notice bibliographique
Résumé
Abstract Activation of human prothrombin (Pro) occurs following two cleavages by membrane-bound factor Xa (fXa) (Arg271 followed by Arg320, generating prethrombin 2 as intermediate). Binding of factor Va (fVa) to fXa on a membrane surface in the presence of divalent metal ions results in the formation of prothrombinase (IIase). It has been established that IIase is a 1:1 stochiometric complex between fVa and fXa on a lipid surface. This complex catalyzes the activation of Pro following the opposite pathway (cleavage at Arg320 followed by Arg271, generating meizothrombin as intermediate). Thus, the activity of factor Xa within IIase is controlled by fVa. Most of the data published in the literature on IIase function was obtained using limiting amounts of fXa in the presence of saturating concentrations of fVa. It is always assumed that IIase acts as one enzyme and that fXa needs to be saturated with fVa. However, if IIase is one enzyme, theoretically reversing the concentrations of reactants will have no effect on the pathway and catalytic efficiency of the enzyme for cleavage of Pro. We have assessed the pathway to thrombin formation in the presence of high or low concentrations of fVa (with respect to fXa). In the absence of fVa, fXa (10nM) activates Pro slowly through initial cleavage at Arg271. Very little thrombin is formed under these conditions. In the presence of 10nM fXa and 100pM fVa there is a significant increase in the concentration of thrombin as demonstrated by the increase in the appearance of the B chain of thrombin. Under these experimental conditions Pro is activated through the pathway characterized by the appearance of prethrombin 2 as intermediate. No fragment 1·2-A was apparent. In the presence of 100pM fXa with 10nM fVa, Pro is activated exclusively through the pathway characterized by the appearance of meizothrombin as demonstrated by the presence of fragment 1·2-A and the absence of prethrombin 2. Kinetics assessments of thrombin generation using both conditions revealed that the kcat for thrombin generation by IIase assembled in the presence of low concentrations of fVa is ∼240 min−1 while the the kcat of IIase assembled with saturating concentrations of fVa is ∼2100 min−1. These data were verified by studying the activation of recombinant Pro that can only be cleaved at Arg320 (rMZ). In the presence of limiting concentrations of fVa, rMZ was cleaved with a rate that is approximately 7-10-fold slower than the rate of rMZ cleavage in the presence of saturating concentrations of fVa. Overall our data support the following hypothesis: in the presence of low concentrations of fVa that are generated during initiation of clotting, IIase activates Pro through initial cleavage at Arg271 (E271). As clotting occurs and more fVa is generated, a new form of IIase is formed following the binding of fXa to fVa and the interaction of the complex with Pro (E320). Under these conditions, while both forms of IIase exist, E320 that has higher catalytic efficiency activates Pro via initial cleavage at Arg320. Our data are in agreement with recent findings that have suggested that IIase activation of Pro may be best described as an ordered ping-pong reaction and imply that the concentration of fVa generated during clotting, dictates which form of IIase will first cleave Pro. In conclusion, our findings suggest that fVa shuttling between E271 and E320 directs Pro activation by factor Xa locally at the place of vascular injury.
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 machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,001 | 0,002 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,001 |
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 source (Gemma direct ou Codex distillé), 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 ».