Channeling During Prothrombin Activation
Bibliographic record
Abstract
The plasma zymogen prothrombin (II) is converted to the clotting enzyme thrombin (IIa) by two prothrombinase-catalyzed proteolytic cleavages. Thus, two intermediates, meizothrombin (mIIa) and prethrombin-2 (P2), are possible on the reaction pathway. Measurements of the time courses of II, mIIa, P2, and IIa suggested a channeling phenomenon, whereby a portion of the II is converted directly to IIa without free mIIa and P2 as obligatory intermediates. Evidence for this was that the maximum rate of IIa formation preceded the maximum in the level of either intermediate. In addition, analysis of the data according to a model that included two parallel pathways through mIIa and P2 indicated that about 40% of the II consumed did not yield free mIIa or P2. Further studies were carried out in which II was continuously infused in a reactor at a constant rate. Under these conditions II, mIIa, and P2 reached constant steady-state levels, and IIa was produced at a constant rate, equal to that of II infusion. During the steady state, traces of II, mIIa, and P2 were introduced as radiolabels. Time courses of isotope consumption were first order, thus allowing the rates of consumption of II, mIIa, and P2 to be calculated. Under these conditions the rate of II consumption equaled the rate of IIa formation. Rates of consumption of the free intermediates, however, were only 22 (mIIa) and 15% (P2), respectively, of the rate of thrombin formation. Thus, both the time course experiments and the steady-state experiments indicate that an appreciable fraction of II is channeled directly to IIa without proceeding through the free intermediates mIIa and P2.
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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 | 0.001 |
| 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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 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".