Related Experiment Videos
Comparative studies on amino and thiol groups in myosins from different sources
Biochimica Et Biophysica Acta
|November 8, 1976
Summary
Essential amino groups are crucial for myosin function in skeletal and heart muscles, but not in gizzard or platelet myosins. Alkylation of thiol groups affects ATPase activity differently across various myosin types.
Area of Science:
- Biochemistry
- Molecular Biology
- Muscle Physiology
Background:
- Myosins are essential motor proteins involved in muscle contraction.
- Understanding the chemical modification of myosins provides insights into their structure-function relationships.
- Specific amino and thiol groups are critical for myosin enzymatic activity.
Purpose of the Study:
- To investigate the role of amino and thiol groups in the enzymatic activity of various myosins.
- To determine the effect of chemical modifications on K+-activated and Ca(2+)-activated ATPase activities.
- To explore the influence of nucleotides like Mg-ADP on these modifications and activities.
Main Methods:
- Myosins from different muscle sources (rabbit skeletal, rabbit heart, fish skeletal, chicken gizzard, human platelets) were chemically modified.
- Trinitrophenylation (using trinitrobenzene sulfonate) targeted amino groups.
- Alkylation (using N-ethylmeleimide) targeted thiol groups.
- Spectrophotometric and enzymatic assays were used to monitor reactions and enzyme activity.
- Reactions were performed in the presence or absence of Mg-ADP.
Main Results:
- Essential amino groups, critical for enzymatic characteristics, were identified in skeletal and heart myosins but absent in gizzard and platelet myosins.
- The modification of these essential amino groups was significantly slowed by Mg-ADP.
- Alkylation of thiol groups universally abolished K+-activated ATPase activity, with varying rates depending on myosin source, nucleotides, and ionic strength.
- Ca(2+)-activated ATPase activity was modulated by alkylation; it increased in the absence of Mg-ADP but showed a transient peak in its presence, with variations based on myosin origin.
Conclusions:
- Specific amino groups are vital for the function of myosins in cardiac and skeletal muscles.
- Thiol groups are essential for maintaining K+-activated ATPase activity across all studied myosins.
- Nucleotides, particularly Mg-ADP, play a regulatory role in the chemical modification and subsequent enzymatic activity of myosins.