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Heterogeneity in the actin activation of myosin
Abstract:
The soluble proteolytic fragments of myosin, heavy meromyosin and subfragment 1, were prepared with varying amounts of the proteases chymotrypsin and papain, respectively. The actin-activated ATP hydrolysis were examined with oxygen-18-labeled ATP. Each preparation of heavy meromyosin and subfragments 1 displayed two pathways of ATP hydrolysis, called respectively the high and low oxygen exchange mechanisms. The contributions of the two mechanisms were found to be sensitive to the potassium chloride concentration. With a fixed concentration of actin (300 microM), the contribution of the low-exchange mechanism decreased from a maximum of 90% of the ATP hydrolysis at 10 and 20 mM KCl to 12% at 180 mM KCl. The results suggested that the two mechanisms were competing reactions catalyzed by a single species of myosin.
Insights
Myosin fragments exhibit two ATP hydrolysis pathways: high and low oxygen exchange mechanisms. Potassium chloride concentration influences the contribution of these pathways, suggesting they are competing reactions from a single myosin species.
Area of Science:
- Biochemistry
- Molecular Biology
- Muscle Physiology
Background:
- Myosin is a key motor protein responsible for muscle contraction.
- Understanding the mechanisms of ATP hydrolysis by myosin is crucial for elucidating muscle function.
- Proteolytic fragmentation of myosin yields functional sub-units like heavy meromyosin (HMM) and subfragment 1 (S1).
Purpose of the Study:
- To investigate the pathways of ATP hydrolysis by heavy meromyosin (HMM) and subfragment 1 (S1).
- To determine the influence of potassium chloride (KCl) concentration on these hydrolysis pathways.
- To explore the relationship between different ATP hydrolysis mechanisms in myosin.
Main Methods:
- Preparation of HMM and S1 using chymotrypsin and papain, respectively.
- Measurement of actin-activated ATP hydrolysis using oxygen-18-labeled ATP.
- Analysis of ATP hydrolysis pathways under varying KCl concentrations.
Main Results:
- HMM and S1 preparations demonstrated two distinct ATP hydrolysis pathways: high and low oxygen exchange mechanisms.
- The relative contribution of the low-exchange mechanism was highly sensitive to KCl concentration.
- At fixed actin concentration, the low-exchange mechanism's contribution decreased from 90% at 10-20 mM KCl to 12% at 180 mM KCl.
Conclusions:
- The study identified two competing ATP hydrolysis mechanisms in myosin fragments.
- These mechanisms are catalyzed by a single myosin species, with their contributions modulated by KCl concentration.
- This finding provides insights into the dynamic regulation of myosin's enzymatic activity.