Effects of substituting uridine triphosphate for ATP on the crossbridge cycle of rabbit muscle
Bibliographic record
Abstract
1. Substituting uridine triphosphate (UTP) for ATP as a substrate for rabbit skeletal myosin and actin at 4 degrees C slowed the dissociation of myosin-S1 from actin by threefold, and hydrolysis of the nucleotide by sevenfold, without a decrease in the rates of phosphate or uridine diphosphate dissociation from actomyosin. 2. The same substitution in skinned rabbit psoas fibres at 2-3 degrees C reduced the maximum shortening velocity by 56 % and increased the force asymptote of the force-velocity curve relative to force (alpha/P(o)) by 112 % without altering the velocity asymptote, beta. It also decreased isometric force by 35 % and isometric stiffness by 20 %, so that the stiffness/force ratio was increased by 23 %. 3. Tension transient experiments showed that the stiffness/force increase was associated with a 10 % reduction in the amplitude of the rapid, partial (phase 2) recovery relative to the isometric force, and the addition of two new components, one that recovered at a step-size-independent rate of 100 s(-1) and another that did not recover following the length change. 4. The increased alpha/P(o) with constant beta suggests an internal load, as expected of attached crossbridges detained in their movement. An increased stiffness/force ratio suggests a greater fraction of attached bridges in low-force states, as expected of bridges with unhydrolyzed UTP detained in low-force states. Decreased phase 2 recovery suggests the detention of high-force bridges, as expected of slowed actomyosin dissociation by nucleotide. 5. These results suggest that the separation of hydrolysed phosphates from nucleotides occurs early in the attached phase of the crossbridge cycle, near and possibly identical to a transition to a firmly attached, low-force state from an initial state where bridges with hydrolysed nucleotides are easily detached by shortening.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.001 | 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 | 0.001 | 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 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".