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Nucleotide regulatory sites on skeletal myosin
M S Laborda-Santesteban1, M J López-Unzu, M J López-Zabalza
1Departamento de Bioquímica, Universidad de Navarra, Pamplona, Spain.
Abstract:
Myosin Ca2+-ATPase activity decreased in the presence of ADP. Free ATP acted either as an activator or as an inhibitor depending on its concentration. The inhibition caused by ADP or ATP followed a competitive pattern with respect to the substrate. ATP, at activating concentrations, competed with dinitrophenol and with the anions SCN-, CN- and HCO3- for the same binding sites of myosin, whereas ADP did not compete with them. These results suggest that the nucleotide regulatory site or sites, different from the hydrolytic sites, seem to coincide with the anion binding sites.
Insights
Adenosine diphosphate (ADP) and adenosine triphosphate (ATP) affect myosin Ca2+-ATPase activity. Nucleotide binding sites, distinct from hydrolytic sites, appear to overlap with anion binding sites on myosin.
Area of Science:
- Biochemistry
- Molecular Biology
- Muscle Physiology
Background:
- Myosin Ca2+-ATPase is a crucial enzyme in muscle contraction, responsible for ATP hydrolysis.
- Understanding the regulation of myosin ATPase activity by nucleotides and other molecules is essential for elucidating muscle function.
Purpose of the Study:
- To investigate the effects of ADP and varying concentrations of ATP on myosin Ca2+-ATPase activity.
- To determine the binding interactions of nucleotides and anions at the regulatory and hydrolytic sites of myosin.
Main Methods:
- Enzyme kinetics assays were performed to measure myosin Ca2+-ATPase activity.
- The effects of different concentrations of ADP and ATP were analyzed.
- Competitive inhibition studies were conducted using anions (SCN-, CN-, HCO3-) and dinitrophenol.
Main Results:
- Myosin Ca2+-ATPase activity was inhibited by ADP.
- Free ATP exhibited both activating and inhibitory effects on ATPase activity, concentration-dependently.
- Both ADP and ATP competitively inhibited the substrate, while only ATP competed with anions and dinitrophenol for binding sites.
Conclusions:
- The nucleotide regulatory site(s) on myosin are distinct from the hydrolytic sites.
- These regulatory sites appear to overlap with the anion binding sites.
- This suggests a complex regulatory mechanism for myosin ATPase involving nucleotide and anion interactions.