Related Experiment Video
Updated: Aug 18, 2026

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers
Published on: May 4, 2022
The variable relation between myosin light-chain phosphorylation and actin-activated ATPase activity in chicken
Abstract:
Using pure myosin light-chain kinase and myosin from chicken gizzard and rabbit skeletal actin, we have established the relationship between myosin phosphorylation and actin-activated ATPase activity by varying the concentration of Ca2+ or calmodulin (CaM). By increasing Ca2+ or CaM the extent of myosin phosphorylation increased from 10% to about 100%, the requirements for half-maximal activation being 0.17 microM Ca2+ and 1 nM CaM. ATPase was activated only when a phosphorylation 'threshold' of about 60% was surpassed. By increasing phosphorylation from 60% to 100%, ATPase activity was further stimulated, the relationship between myosin phosphorylation and ATPase activity being curvilinear. Addition of 1 microM tropomyosin lowered the Ca2+ requirement for half-maximal ATPase activity in the prescence of 0.05 microM CaM from 0.4 microM to 0.2 microM but did not affect the maximal ATPAse activity. In addition, the CaM requirement of ATPase activity was also lowered by gizzard tropomyosin at 9 microM Ca2+. The Ca2+/CaM requirement for myosin phosphorylation remained unaffected by tropomyosin. Thus, tropomyosin altered the relationship between myosin phosphorylation and ATPase activity: the phosphorylation 'threshold' was lowered from 60% to about 10%, hence causing a leftward shift of the relationship which becomes similar to that in the case of native actomyosin.
More Related Videos
08:50The Mechanics of (Poro-)Elastic Contractile Actomyosin Networks As a Model System of the Cell Cytoskeleton
Published on: March 10, 2023
12:35Optogenetic Inhibition of Rho1-Mediated Actomyosin Contractility Coupled with Measurement of Epithelial Tension in Drosophila Embryos
Published on: April 14, 2023
Related Concept Videos
Cross-bridge Cycle
Overview of Myosin Structure and Function
Actin and Myosin in Muscle Contraction
The Role of Actin and Myosin in Non-muscle Cells
The Sarcomere
Each myosin...
Smooth Muscle Contraction
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...