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Smooth muscle myosin: regulation and properties
Avril V Somlyo1, Alexander S Khromov, Martin R Webb
1Molecular Physiology and Biological Physics, University of Virginia, PO Box 800736, 1300 Jefferson Park Avenue, Charlottesville, VA 22908-0736, USA. avs5u@virginia.edu
Summary
Smooth muscle cross-bridge biochemical states and mechanical events were studied using Pi and ADP release kinetics. ADP release is a regulated step influencing smooth muscle
Area of Science:
- Biochemistry
- Muscle Physiology
- Biophysics
Background:
- Smooth muscle contraction involves complex biochemical states and mechanical events.
- Understanding cross-bridge kinetics is crucial for elucidating muscle function and force generation.
Purpose of the Study:
- To investigate the relationship between biochemical states and mechanical events in smooth muscle cross-bridge cycling.
- To directly measure the kinetics of inorganic phosphate (Pi) and adenosine diphosphate (ADP) release.
Main Methods:
- Direct kinetic measurements of Pi and ADP release from smooth muscle cross-bridges.
- Utilized thiophosphorylated cross-bridges and fluorescent ADP analogue transients.
- Investigated the effects of strain and myosin regulatory light chain (RLC) thiophosphorylation on release rates.
Main Results:
- Pi release from thiophosphorylated cross-bridges was biphasic (1.8 s-1 and 0.3 s-1).
- ADP analogue release was faster in phasic than tonic smooth muscles.
- RLC thiophosphorylation increased, while positive strain decreased, the release rate.
- ADP release kinetics suggest it may limit the ATPase rate and contribute to smooth muscle's economy of force.
Conclusions:
- ADP release is a regulated step in smooth muscle contraction, dependent on strain and dephosphorylation.
- Slow ADP release and high affinity for ADP contribute to the high economy of force in smooth muscle.
- RLC thiophosphorylation induces structural changes modulating cross-bridge product release.