Myosin regulatory light chain phosphorylation and strain modulate adenosine diphosphate release from smooth muscle Myosin.
The effects of myosin regulatory light chain (RLC) phosphorylation and strain on adenosine diphosphate (ADP) release from cross-bridges in phasic (rabbit bladder (Rbl)) and tonic (femoral artery (Rfa)) smooth muscle were determined by monitoring fluorescence transients of the novel ADP analog, 3'-deac-eda-ADP (deac-edaADP). Fluorescence transients reporting release of 3'-deac-eda-ADP were significantly faster in phasic (0.57 +/- 0.06 s(-1)) than tonic (0.29 +/- 0.03 s(-1)) smooth muscles. Thiophosphorylation of regulatory light chains increased and strain decreased the release rate approximately twofold. The calculated (k-ADP/k+ADP) dissociation constant, Kd of unstrained, unphosphorylated cross-bridges for ADP was 0.6 microM for rabbit bladder and 0.3 microM for femoral artery. The rates of ADP release from rigor bridges and reported values of Pi release (corresponding to the steady-state adenosine triphosphatase (ATPase) rate of actomyosin (AM)) from cross-bridges during a maintained isometric contraction are similar, indicating that the ADP-release step or an isomerization preceding it may be limiting the adenosine triphosphatase rate. We conclude that the strain- and dephosphorylation-dependent high affinity for and slow ADP release from smooth muscle myosin prolongs the fraction of the duty cycle occupied by strongly bound actomyosin.ADP state(s) and contributes to the high economy of force.
Khromov
Alexander S
AS
Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.
Webb
Martin R
MR
Ferenczi
Michael A
MA
Trentham
David R
DR
Somlyo
Andrew P
AP
Somlyo
Avril V
AV
D000205:Actomyosin / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D005456:Fluorescent Dyes / Q000737:chemistry; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism*; D010766:Phosphorylation; D011817:Rabbits; D024745:Smooth Muscle Myosins / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism
D005456:Fluorescent Dyes; D018994:Myosin Light Chains; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D024745:Smooth Muscle Myosins