Angol nyelvű Tudományos Szakcikk (Folyóiratcikk)

- SJR Scopus - Biophysics: D1

Azonosítók

- MTMT: 31915329
- DOI: 10.1016/j.bpj.2020.09.004
- WoS: 000579362500007
- Scopus: 85092063341
- PubMed: 33010234

It is controversial whether the phosphate (Pi) release step in the cross-bridge cycle
occurs before or after the first tension-generating step and whether it is fast or
slow. We have therefore modified our previous model of the frog cross-bridge cycle
by including a Pi release step either before (model A) or after (model B) the first
tension-generating step and refined the two models by downhill simplex runs against
experimental data for the force-velocity relation and the tension transients after
length steps. Pi release step was initially made slow (70 s-1), but after refinement,
it became fast (∼500 s-1 for model A and ∼6000 s-1 for model B). The two models gave
similar fits to the experimental tension transients after length steps, but model
A gave a better fit to the lengthening limb of the force-velocity relation than model
B. 50 mM Pi inhibited the isometric tension of model A by ∼50% but that of model B
by only ∼25%. The half-inhibition was at 6.0 mM Pi for model A and at 1.6 mM Pi for
model B. The values for model A were consistent with experimental data. We also simulated
the effect Pi jump as in caged Pi experiments. For model A, a Pi jump induced a tension
fall at a rate similar to the experimental phase II. There was then a small rise in
tension to the steady state mimicking the experimental phase III. The initial tension
fall was caused by detachment of M⋅ADP⋅Pi myosin heads from actin and reversal of
the first tension-generating step. For model B, the fall in tension was more rapid
and due to reversal of the first tension-generating step, and phase III was not observed.
We conclude that, as in model A, the Pi release step is before the first tension-generating
step and is moderately fast.

2021-05-07 12:27