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ATPase activity and filament formation of partially purified myosin from leucocytes
Abstract:
Myosin was isolated from leucocytes in horse arterial blood by the same procedures used for the isolation of myosin from skeletal muscle. The Ca2+-, EDTA-, and Mg2+-ATPase [EC 3.6.1.3] activities of the protein was 0.148, 0.147, and 0.001 mumoles/min/mg, respectively, in 0.5 M KCl at pH 7.0 and 25 degrees. The Ca2+-ATPase activity decreased with decrease in the ionic strength. No difference was found between leucocyte myosin and skeletal myosin in the pH profiles of Ca2+- and EDTA-ATPases. The rate and amount of the initial burst of Pi liberation of leucocyte myosin were 0.002 mumoles/min/mg and 0.83 moles/4.8 X 10(5)g, respectively. Leucocyte myosin aggregated into filaments of 0.3 mum length and 150 A diameter, which had a bare shaft and irregular projections. At high ionic strength, the protein bound to skeletal muscle F-actin to form a complex with the characteristic arrowhead structure.
Insights
Leukocyte myosin from horse blood shares properties with skeletal muscle myosin, including ATPase activity and actin binding. This finding suggests a conserved structure and function across different myosin types.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Myosin is a crucial protein for muscle contraction and cellular motility.
- Understanding myosin's role in non-muscle cells, like leukocytes, is important for cell function research.
Purpose of the Study:
- To isolate and characterize myosin from horse arterial leukocytes.
- To compare the biochemical and structural properties of leukocyte myosin with skeletal muscle myosin.
Main Methods:
- Myosin isolation using established skeletal muscle myosin procedures.
- Enzymatic assays to determine Ca2+-, EDTA-, and Mg2+-ATPase activities.
- Analysis of pH profiles and ionic strength effects on ATPase activity.
- Investigation of Pi liberation kinetics.
- Filament formation and F-actin binding studies.
Main Results:
- Leukocyte myosin exhibited Ca2+-, EDTA-, and Mg2+-ATPase activities comparable to skeletal muscle myosin.
- Ca2+-ATPase activity was sensitive to ionic strength.
- pH profiles for Ca2+- and EDTA-ATPases were similar between leukocyte and skeletal myosins.
- Leukocyte myosin formed filaments and bound to F-actin, forming arrowhead complexes.
Conclusions:
- Horse arterial leukocyte myosin is biochemically and structurally similar to skeletal muscle myosin.
- These findings suggest conserved functional domains and structural characteristics of myosin across different cell types.
- Leukocyte myosin's interaction with actin supports its potential role in cellular processes within leukocytes.