Cooperative turning on of myosin subfragment 1 adenosine triphosphatase activity by the troponin-tropomyosin-actin complex

Biochemistry ◽  
1988 ◽  
Vol 27 (18) ◽  
pp. 6987-6993 ◽  
Author(s):  
David L. Williams ◽  
Lois E. Greene ◽  
Evan Eisenberg
Keyword(s):  
Adenosine Triphosphatase ◽  
Adenosine Triphosphatase Activity ◽  
Myosin Subfragment ◽  
Myosin Subfragment 1

scholarly journals The characterization of myosin–product complexes and of product-release steps during the magnesium ion-dependent adenosine triphosphatase reaction

1974 ◽  
Vol 141 (2) ◽  
pp. 331-349 ◽  
Author(s):  
Clive R. Bagshaw ◽  
David R. Trentham
Keyword(s):  
Adenosine Triphosphatase ◽  
Elementary Processes ◽  
Product Release ◽  
Dissociation Equilibrium ◽  
Fluorescence Measurements ◽  
Myosin Subfragment ◽  
Myosin Subfragment 1 ◽  
In Series ◽  
Pi Complex

Evidence is presented that the myosin subfragment-1–ADP complex, generated by the addition of Mg2+ and ADP to subfragment 1, is an intermediate within the myosin Mg2+-dependent adenosine triphosphatase (ATPase) turnover cycle. The existence of this species as a steady-state intermediate at pH8 and 5°C is demonstrated by fluorescence measurements, but its concentration becomes too low to measure at 21°C. This arises because there is a marked temperature-dependence on the rate of the process controlling ADP dissociation from subfragment 1 (rate=1.4s-1 at 21°C, 0.07s-1 at 5°C). In the ATPase pathway this reaction is in series with a relatively temperature-insensitive process, namely an isomerization of the subfragment-1–product complex (rate=0.055s-1 at 21°C, 0.036s-1 at 5°C). By means of studies on the Pi inhibition of nucleotide-association rates, a myosin subfragment-1–Pi complex was characterized with a dissociation equilibrium constant of 1.5mm. Pi appears to bind more weakly to the myosin subfragment-1–ADP complex. The studies indicate that Pi dissociates from subfragment 1 at a rate greater than 40s-1, and substantiates the existence of a myosin-product isomerization before product release in the elementary processes of the Mg2+-dependent ATPase. In this ATPase mechanism Mg2+ associates as a complex with ATP and is released as a complex with ADP. In 0.1m-KCl at pH8 1.0mol of H+ is released/mol of subfragment 1 concomitant with the myosin-product isomerization or Pi dissociation, and 0.23 mol of H+ is released/mol of subfragment when ATP binds to the protein, but 0.23 mol of H+ is taken up again from the medium when ADP dissociates. Within experimental sensitivity no H+ is released into the medium in the step involving ATP cleavage.

Structure of Myosin Subfragment-1 from Electron Microscopy and Crystallography

1988 ◽  
Vol 46 ◽  
pp. 156-157
Author(s):  
Donald A. Winkelmann
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Actin Filaments ◽  
Light Chains ◽  
Myosin Filament ◽  
Primary Role ◽  
Heavy Chains ◽  
Myosin Subfragment ◽  
Myosin Subfragment 1 ◽  
Globular Head

The primary role of the interaction of actin and myosin is the generation of force and motion as a direct consequence of the cyclic interaction of myosin crossbridges with actin filaments. Myosin is composed of six polypeptides: two heavy chains of molecular weight 220,000 daltons and two pairs of light chains of molecular weight 17,000-23,000. The C-terminal portions of the myosin heavy chains associate to form an α-helical coiled-coil rod which is responsible for myosin filament formation. The N-terminal portion of each heavy chain associates with two different light chains to form a globular head that binds actin and hydrolyses ATP. Myosin can be fragmented by limited proteolysis into several structural and functional domains. It has recently been demonstrated using an in vitro movement assay that the globular head domain, subfragment-1, is sufficient to cause sliding movement of actin filaments.The discovery of conditions for crystallization of the myosin subfragment-1 (S1) has led to a systematic analysis of S1 structure by x-ray crystallography and electron microscopy. Image analysis of electron micrographs of thin sections of small S1 crystals has been used to determine the structure of S1 in the crystal lattice.

scholarly journals Studies of Ligand-induced Conformational Perturbations in Myosin Subfragment 1

1989 ◽  
Vol 264 (18) ◽  
pp. 10810-10819
Author(s):  
K N Rajasekharan ◽  
M Mayadevi ◽  
M Burke
Keyword(s):  
Myosin Subfragment ◽  
Myosin Subfragment 1
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