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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Various aspects of actin--myosin interaction were studied with actin preparations from two types of smooth muscle: bovine aorta and chicken gizzard, and from two types of sarcomeric muscle: bovine cardiac and rabbit skeletal. All four preparations activated the Mg2+-ATPase activity of skeletal muscle myosin to the same Vmax, but the Kapp for the smooth muscle preparations was higher. At low KCl, pH 8.0 and millimolar substrate concentrations the Kapp values differed by a factor of 2.5. This differential behaviour of the four actin preparations correlates with amino acid substitutions at positions 17 and 89 of actin polypeptide chain, differentiating the smooth-muscle-specific gamma and alpha isomers from cardiac and skeletal-muscle-specific alpha isomers. This correlation provides evidence for involvement of the NH2-terminal portion of the actin polypeptide chain in the interaction with myosin. The differences in the activation of myosin ATPase by various actins were sensitive to changes in the substrate and KCl concentration and pH of the assay medium. Addition of myosin subfragment-1 or heavy meromyosin in the absence of nucleotide produced similar changes in the fluorescence of a fluorescent reagent N-(1-pyrenyl)-iodoacetamide, attached at Cys-374, or 1,N6-ethenoadenosine 5'-diphosphate substituted for the bound ADP in actin protomers in gizzard and skeletal muscle F-actin. The results are consistent with an influence of the amino acid substitutions on ionic interactions leading to complex formation between actin and myosin intermediates in the ATPase cycle but not on the associated states.
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PMID:Identification of amino acid substitutions differentiating actin isoforms in their interaction with myosin. 293 50

After 10 wash cycles, 0.8 u.e. of creatine kinase activity remained bound per mg of chicken pectoralis myofibrils which had been freed of soluble creatine kinase, mitochondria, and membranes. The bound creatine kinase is located at the M-band and contributes to the electron density of this sarcomeric structure (Wallimann, T., Pelloni, G.W., Turner, D.C., and Eppenberger, H. M. (1978) Proc. Natl. Acad. Sci. U. S. A. 75, 4296-4300). By measuring the combined actin-activated Mg2+-ATPase and creatine kinase reactions of myofibrils by pH-stat, it was shown that the amount of M-line-bound creatine kinase activity was sufficient to rephosphorylate the ATP hydrolyzed in vitro by the actin-activated Mg2+-ATPase. The amount of M-line-bound creatine kinase and thus the ATP regeneration potential depended on the muscle type. It was higher in fast muscles and lower in slow muscles. Inhibition of myofibrillar creatine kinase or extraction of the M-line-bound enzyme abolished the ATP regeneration potential without affecting ATPase activity. Inhibitors of myokinase, mitochondrial ADP/ATP translocase, and respiration did not affect the ATP regeneration potential or the ATPase. M-line-bound creatine kinase, sufficient to support an ATP turnover rate of 6s-1 per myosin head, seems to have the capacity for the intramyofibrillar regeneration of most or all of the ATP hydrolyzed by the myofibrillar ATPase during muscle contraction. Thus, M-line-bound creatine kinase at the myofibrillar receiving end of the phosphorylcreatine shuttle is of physiological significance.
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PMID:Function of M-line-bound creatine kinase as intramyofibrillar ATP regenerator at the receiving end of the phosphorylcreatine shuttle in muscle. 614 55

Leiomodin proteins are vertebrate homologues of tropomodulin, having a role in the assembly and maintenance of muscle thin filaments. Leiomodin2 contains an N-terminal tropomodulin homolog fragment including tropomyosin-, and actin-binding sites, and a C-terminal Wiskott-Aldrich syndrome homology 2 actin-binding domain. The cardiac leiomodin2 isoform associates to the pointed end of actin filaments, where it supports the lengthening of thin filaments and competes with tropomodulin. It was recently found that cardiac leiomodin2 can localise also along the length of sarcomeric actin filaments. While the activities of leiomodin2 related to pointed end binding are relatively well described, the potential side binding activity and its functional consequences are less well understood. To better understand the biological functions of leiomodin2, in the present work we analysed the structural features and the activities of Rattus norvegicus cardiac leiomodin2 in actin dynamics by spectroscopic and high-speed sedimentation approaches. By monitoring the fluorescence parameters of leiomodin2 tryptophan residues we found that it possesses flexible, intrinsically disordered regions. Leiomodin2 accelerates the polymerisation of actin in an ionic strength dependent manner, which relies on its N-terminal regions. Importantly, we demonstrate that leiomodin2 binds to the sides of actin filaments and induces structural alterations in actin filaments. Upon its interaction with the filaments leiomodin2 decreases the actin-activated Mg2+-ATPase activity of skeletal muscle myosin. These observations suggest that through its binding to side of actin filaments and its effect on myosin activity leiomodin2 has more functions in muscle cells than it was indicated in previous studies.
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PMID:Cardiac leiomodin2 binds to the sides of actin filaments and regulates the ATPase activity of myosin. 2902 66