Activation of actin-cardiac myosin subfragment 1 magnesium-ATPase rate by calcium shows cooperativity intrinsic to the thin filament
- 1 January 1987
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 26 (2), 492-497
- https://doi.org/10.1021/bi00376a022
Abstract
The magnesium adenosinetriphosphatase (MgATPase) rate of cardiac myosin subfragment 1 (S-1) was studied in the presence of regulated actin in order to investigate the mechanism by which Ca2+ cooperatively induces cardiac muscle contraction. The MgATPase rate increased cooperatively with Ca2+, exhibiting a Hill coefficient of 1.8 and 50% activation at pCa 5.75. This cooperative response occurred despite an experimental design excluding several potential sources of cooperativity. First, to exclude spurious cooperativity due to erroneous calculation of pCa at low ionic strength, the affinities of Ca2+ and Mg2+ for [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) were measured by a novel method using Quin 2. At pH 7.06, 25.degree. C, and .mu. = 30 mM, the KD was 140 nM for CaEGTA and 2.7 mM for MgEGTA. Second, the cooperativity was not produced by actin-myosin S-1 binding; myosin S-1 was bound to only 1 of every 300 actin promoters, and earlier work [Tobacman, L.S., and Adelstein, R. S. (1986) Biochemistry 25, 798-802] had shown that cardiac myosin S-1 binds with equal affinity to the thin filament at very low Ca2+ and at saturating Ca2+ concentrations. Furthermore, the adenosine 5''-triphosphate turnover rate of the myosin S-1 was independent of enzyme concentration at low, intermediate, and saturating Ca2+ concentrations. Finally, since cardiac troponin has only one regulatory Ca2+-specific site, cooperative interactions between such sites could not occur. These data suggest that part of the cooperativity conferred by interaction between adjacent troponin-tropomyosin complexes is intrinsic to the thin filament and independent of myosin.This publication has 32 references indexed in Scilit:
- The calcium and magnesium binding sites on cardiac troponin and their role in the regulation of myofibrillar adenosine triphosphatase.Journal of Biological Chemistry, 1980
- Kinetic studies of the cooperative binding of subfragment 1 to regulated actin.Proceedings of the National Academy of Sciences, 1980
- A fluorescent probe study of Ca2+ binding to the Ca2+-specific sites of cardiac troponin and troponin C.Journal of Biological Chemistry, 1980
- Can the binding of Ca2+ to two regulatory sites on troponin C determine the steep pCa/tension relationship of skeletal muscle?Proceedings of the National Academy of Sciences, 1980
- Neutral carrier ion-selective microelectrodes for measurement of intracellular free calciumBiochimica et Biophysica Acta (BBA) - Biomembranes, 1980
- Theoretical model for the cooperative equilibrium binding of myosin subfragment 1 to the actin-troponin-tropomyosin complex.Proceedings of the National Academy of Sciences, 1980
- Cooperative binding of myosin subfragment-1 to the actin-troponin-tropomyosin complex.Proceedings of the National Academy of Sciences, 1980
- Equilibrium of the actin-tropomyosin interactionJournal of Molecular Biology, 1979
- Modulation of Ca2+ control of dog and rabbit cardiac myofibrils by Mg2+. Comparison with rabbit skeletal myofibrils.Circulation Research, 1976
- Ca2+ dependence of tension and ADP production in segments of chemically skinned muscle fibersBiochimica et Biophysica Acta (BBA) - Bioenergetics, 1976