A tight-binding interaction between smooth-muscle native thin filaments and heavy meromyosin in the presence of MgATP.
The binding of the Ca2+-regulated native thin filaments from vascular smooth muscle to vascular smooth-muscle heavy meromyosin was measured in the presence of 3 mM-MgATP. At 25 degrees C and I 0.25 binding had an affinity of 1 X 10(-6)-0.3 X 10(-6) M-1 with a stoichiometry of one molecule bound to one actin monomer. The Km for the activation of heavy-meromyosin ATPase was 20-50 microM. Thin filament-heavy meromyosin binding was not altered by Ca2+ (pCa 9-4) or the extent of myosin phosphorylation. With skeletal-muscle heavy meromyosin affinity was 0.023 X 10(6) M-1 in parallel with activation of the ATPase (Km 54 microM). It is concluded that tight binding is specific to smooth-muscle proteins and that it is not related to the ATPase activation site.
Marston
S B
SB
National Heart and Lung Institute, London, U.K.
D008841:Actin Cytoskeleton / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D004789:Enzyme Activation; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism
D015879:Myosin Subfragments; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D002118:Calcium