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Related Experiment Videos

Kinetic differences in cardiac myosins with identical loop 1 sequences.

J S Pereira1, D Pavlov, M Nili

  • 1Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.

The Journal of Biological Chemistry
|November 15, 2000
PubMed
Summary

Differences in rat and pig beta-myosin heavy chains (beta-MHC) kinetics are not due to Loop 1. ADP release rates, not Loop 1 sequence, drive variations in nucleotide turnover between these myosin isoforms.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Physiology

Background:

  • Vertebrate type II myosin isoforms exhibit varied nucleotide turnover kinetics, potentially linked to ADP release rates.
  • Surface loops, specifically Loop 1 (ATPase loop) and Loop 2 (actin binding loop), are hypothesized to regulate ADP release.

Purpose of the Study:

  • To investigate the kinetic properties of rat and pig beta-myosin heavy chains (beta-MHC).
  • To determine the role of Loop 1 sequence in the differing nucleotide turnover kinetics between rat and pig beta-MHC.

Main Methods:

  • Comparative analysis of Loop 1 sequences in rat and pig beta-MHC.
  • Measurement of unloaded shortening velocity in skinned ventricular myocytes.
  • Determination of actin-activated ATPase activity.

Related Experiment Videos

  • Stopped-flow kinetics to assess acto-myosin dissociation and ADP release rates.
  • Measurement of ATP cleavage rates.

    • Main Results:

    • Rat and pig beta-MHC Loop 1 sequences are nearly identical, with only a single conservative substitution.
    • Unloaded shortening velocity was significantly higher in rat beta-MHC (1.1 muscle lengths/s) compared to pig beta-MHC (0.35 muscle lengths/s).
    • Actin-activated ATPase activity and ATP cleavage rates were higher for rat beta-MHC.
    • ADP release rate was approximately 3.8-fold faster for rat beta-MHC than for pig beta-MHC, while MgATP-induced dissociation rates were similar.
    • Loop 1 sequence identity contrasts with functional kinetic differences.

    Conclusions:

    • Loop 1 sequence does not account for the large differences in nucleotide turnover kinetics between rat and pig beta-myosin.
    • The observed kinetic variations are attributed to sequence differences in other regions of the myosin heavy chain (MHC) backbone.
    • ADP release rate is a key determinant of the differing turnover kinetics between these beta-myosin isoforms.