Abstract
We studied the conformational changes in actin filaments induced by the binding of calponin or a 38-kDa fragment of caldesmon, two actin-binding proteins known to inhibit actin-activated ATP hydrolysis by phosphorylated smooth muscle myosin. The F-actinin myosin-free muscle fibers (ghost fibers) was labeled with fluorescein-5-maleimide and the conformational change in actin was determined by polarized fluorimetry. Data show that both calponin and the 38-kDa caldesmon fragment inhibit the conformational changes in F-actin that are compatible with the "strong-binding" state between myosin heads and actin. Tropomyosin slightly reduced the effect produced by calponin, but enhances the effect produced by the 38-kDa caldesmon fragment.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Actins / chemistry*
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Actins / metabolism*
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Animals
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Calcium-Binding Proteins / metabolism*
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Calcium-Binding Proteins / pharmacology
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Calmodulin-Binding Proteins / metabolism*
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Calmodulin-Binding Proteins / pharmacology
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Calponins
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Chickens
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Cross-Linking Reagents / pharmacology
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Ethylmaleimide / pharmacology
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Gizzard, Avian
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Maleimides / pharmacology
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Microfilament Proteins
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Muscle Fibers, Skeletal / physiology*
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Muscle Proteins / metabolism
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Muscle Proteins / pharmacology
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Muscle, Skeletal / physiology*
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Muscle, Smooth / physiology
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Myosins / metabolism
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Peptide Fragments / metabolism
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Peptide Fragments / pharmacology
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Protein Binding
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Protein Conformation
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Rabbits
Substances
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Actins
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Calcium-Binding Proteins
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Calmodulin-Binding Proteins
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Cross-Linking Reagents
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Maleimides
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Microfilament Proteins
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Muscle Proteins
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Peptide Fragments
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Myosins
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Ethylmaleimide