Interactions of the two heads of scallop (Argopecten irradians) heavy meromyosin with actin: influence of calcium and nucleotides

Nyitrai, Miklos and Szent-Gyorgyi, Andrew G. and Geeves, Michael A. (2003) Interactions of the two heads of scallop (Argopecten irradians) heavy meromyosin with actin: influence of calcium and nucleotides. Biochemical Journal, 370 (Pt 3). pp. 839-848. ISSN 0264-6021. (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)

The full text of this publication is not available from this repository. (Contact us about this Publication)
Official URL


We recently proposed a co-operative model for the influence of calcium and ADP on scallop ( Argopecten irradians ) muscle heavy meromyosin (scHMM), in which scHMM exists in two conformations (designated 'off' and 'on'), and calcium and ADP are allosteric effectors of the equilibrium between the off and on conformations [Nyitrai, Szent-Gyorgyi and Geeves (2002) Biochem. J. 365, 19-30]. Here we examine the influence of actin on scHMM. In the absence of nucleotide, both heads of scHMM bind very tightly to actin, independent of the presence of calcium. In the absence of calcium, ADP dissociates scHMM from actin completely, and little evidence of ternary complex formation can be found (actin affinity >20 microM). The off state of scHMM therefore does not interact with actin. In the presence of calcium, ADP and actin lower each other's affinity for scHMM by 30-50-fold, although both heads remain strongly attached to actin (actin affinity 0.17 microM). Detailed analysis suggests that the second head contributes far more to the overall binding energy than is the case for mammalian skeletal muscle HMM. This is consistent with a different stereochemical relationship between the two heads in scallop and mammalian HMM molecules.

Item Type: Article
Additional information: 0264-6021 (Print) Journal Article
Uncontrolled keywords: Actins/*metabolism Adenosine Diphosphate/metabolism Adenosine Triphosphate/metabolism Animals Calcium/*metabolism Mollusca/*chemistry Muscle, Skeletal/chemistry/metabolism Myosin Subfragments/*metabolism Nucleotides/*metabolism Protein Binding Protein Conformation Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, P.H.S. Spectrometry, Fluorescence
Subjects: Q Science
Divisions: Faculties > Science Technology and Medical Studies > School of Biosciences
Depositing User: Michael Geeves
Date Deposited: 14 Mar 2009 16:21
Last Modified: 16 Apr 2014 11:08
Resource URI: (The current URI for this page, for reference purposes)
  • Depositors only (login required):