Biophysical Reviews

, Volume 7, Issue 1, pp 5–14 | Cite as

The role of super-relaxed myosin in skeletal and cardiac muscle

  • James W. McNamara
  • Amy Li
  • Cristobal G. dos Remedios
  • Roger Cooke


The super-relaxed (SRX) state of myosin was only recently reported in striated muscle. It is characterised by a sub-population of myosin heads with a highly inhibited rate of ATP turnover. Myosin heads in the SRX state are bound to each other along the thick filament core producing a highly ordered arrangement. Upon activation, these heads project into the interfilament space where they can bind to the actin filaments. Thus far, the population and lifetimes of myosin heads in the SRX state have been characterised in rabbit cardiac, and fast and slow skeletal muscle, as well as in the skeletal muscle of the tarantula. These studies suggest that the role of SRX in cardiac and skeletal muscle regulation is tailored to their specific functions. In skeletal muscle, the SRX modulates the resting metabolic rate. Cardiac SRX represents a “reserve” of inactive myosin heads that may protect the heart during times of stress, e.g. hypoxia and ischaemia. These heads may also be called up when there is a sustained demand for increased power. The SRX in cardiac muscle provides a potential target for novel therapies.


Myosin heads Super-relaxation ATP Heart disease 


Conflict of interest

This article does not contain any studies performed by the any of the authors involving animal or human experimentation. J.M., A.L., C.d.R., R.C. each declare that they have no conflict of interest. Figure 3 (B)-(D) was reprinted from Biophysical Journal, 100(8), Hooijman P, Stewart MA, Cooke R, A new state of cardiac myosin with very slow ATP turnover: a potential cardioprotective mechanism in the heart. pp. 1969–1976, 2011, with permission from Elsevier. Figure 1 (B) was reprinted from Current Opinion in Structural Biology, 16(2), Craig R, Woodhead JL, Structure and function of myosin filaments. pp. 204–2012, 2006, with permission from Elsevier.


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Copyright information

© International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • James W. McNamara
    • 1
  • Amy Li
    • 1
  • Cristobal G. dos Remedios
    • 1
  • Roger Cooke
    • 2
  1. 1.Discipline of Anatomy & Histology, Bosch InstituteUniversity of SydneySydneyAustralia
  2. 2.Department of Biochemistry & BiophysicsCardiovascular Research Institute University of CaliforniaSan FranciscoUSA

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