Ionic interactions play a role in the regulatory mechanism of scallop heavy meromyosin

Nyitrai, Miklos and Stafford, W.F. and Szent-Gyorgyi, Andrew G. and Geeves, Michael A. (2003) Ionic interactions play a role in the regulatory mechanism of scallop heavy meromyosin. Biophysical Journal, 85 (2). pp. 1053-62. ISSN 0006-3495 . (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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Heavy meromyosin from scallop (scHMM) striated muscle is regulated by calcium binding to the essential light chain. The regulation can be modeled with a calcium-dependent equilibrium between on and off scHMM conformations. The observed rate constant for mant-ADP dissociation from scHMM is calcium dependent, and we show here that it can be used to define the equilibrium constant (K(eq)) between on and off conformations. The data show that K(eq) is markedly ionic strength dependent, with high salt (>/=200 mM) abolishing the off state even in the absence of calcium and low salt (<50 mM) favoring the off state even in the presence of calcium. Debye-Huckel plots of the equilibrium constant (K(eq)) for the on and off forms gave parallel slopes (5.94 +/- 0.33 and 6.36 +/- 0.17 M(-0.5)) in the presence and absence of calcium. The presence of an equilibrium mixture of two conformations was confirmed by sedimentation data and the effects of ADP, calcium and ionic strength were in qualitative agreement. Thus scHMM exists in two conformations that can be distinguished in sedimentation profiles and by the rate of release of mant-ADP. Increasing salt concentrations biases the system toward the on state, suggesting a role for ionic interactions in stabilizing the off state.

Item Type: Article
Additional information: 0006-3495 (Print) Evaluation Studies Journal Article Validation Studies
Uncontrolled keywords: Adenosine Diphosphate/*analogs & derivatives/*chemistry Animals Anthranilic Acids/*chemistry Calcium/*chemistry Comparative Study Computer Simulation Fractionation, Field Flow Ions/chemistry Kinetics *Models, Chemical Molecular Motors/*chemistry Mollusca/*chemistry Muscle, Skeletal/*chemistry Myosin Subfragments/*chemistry Potassium Chloride/*chemistry Protein Binding Protein Conformation Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. Research Support, U.S. Gov't, P.H.S. Structure-Activity Relationship
Subjects: Q Science
Divisions: Faculties > Science Technology and Medical Studies > School of Biosciences
Depositing User: Michael Geeves
Date Deposited: 14 Mar 2009 16:17
Last Modified: 18 Jul 2014 09:17
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