The binding of Caldesmon to Actin and Its Effect on the ATPase Activity of Soluble Myosin Subfragments in the Presence and Absence of Tropomyosin

• Published in: The Journal of biological chemistry Vol. 264; no. 16; pp. 9602 - 9610
• Main Authors: Velaz, L, Hemric, M E, Benson, C E, Chalovich, J M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 05.06.1989; American Society for Biochemistry and Molecular Biology
• Subjects: actin; Actins - metabolism; Adenosine Triphosphatases - antagonists & inhibitors; Adenosine Triphosphatases - metabolism; Analytical, structural and metabolic biochemistry; Animals; Binding and carrier proteins; Binding Sites; Binding, Competitive; Biological and medical sciences; Calmodulin-Binding Proteins - metabolism; Chickens; Fundamental and applied biological sciences. Psychology; H super(+)-transporting ATP synthase; Kinetics; Muscle, Smooth - enzymology; Muscle, Smooth - metabolism; Muscles - enzymology; Muscles - metabolism; Myosins - physiology; Peptide Fragments - physiology; Proteins; Rabbits; Tropomyosin - pharmacology; Turkeys; Ligand binding; Radiolabelling; Gel electrophoresis; Tropomyosin; ATPase; Actins; Association constant; Rabbit; Contractile protein; Subfragment 1; Lagomorpha; Binding protein; Vertebrata; Mammalia; Enzymatic activity; Myosin; Inhibition; Cooperative phenomenon
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)60573-3

The binding of 125I- and 14C-caldesmon to actin and actin-tropomyosin was studied using a cosedimentation technique and was analyzed by the method of McGhee and von Hippel [1974) J. Mol. Biol. 86, 469–489) for the binding of large ligands to a homogeneous lattice. The binding was adequately described by a single class of binding sites with a stoichiometry between 1:7 and 1:10. The binding exhibited a small degree of positive cooperativity (ω = 5–6) which was the same in the presence and absence of tropomyosin. The association constant for the binding of caldesmon to an isolated binding site was enhanced, from about 6 × 105 to about 1.4 × 106 M−1, by the presence of smooth muscle tropomyosin. Caldesmon inhibited the actin-activated ATPase activity of skeletal myosin subfragment 1 in both the absence and presence of tropomyosin. Maximum inhibition of ATPase activity occurred when one caldesmon molecule bound to seven actin monomers. A greater degree of inhibition was observed in the presence of tropomyosin than in the absence. This greater inhibition cannot be explained totally by the increased strength of binding of caldesmon to actin in the presence of tropomyosin. Finally, Ca2+-calmodulin completely reversed the binding of caldesmon to actin.