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Structural and immunological properties of myosin from human platelet external and internal membranes
1Department of Membrane and Ultrastructure Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Abstract:
Our previous studies indicate that platelets contain two myosin isoforms, one of them localized in the membrane while the other in the cytoplasmic compartment. Structural and functional differences of these myosins have been characterized. In this study two platelet membrane subfractions, the external and the internal membranes, were isolated simultaneously from a crude membrane fraction and their purity was characterized using specific marker enzymes. Myosin was shown to be present in both membrane fractions and its structural and immunological properties were investigated. The electrophoretic mobilities of myosin in both membrane preparations were identical to the mobility of its cytoplasmic counterpart. Two-dimensional peptide mapping of the iodinated tryptic peptides of the myosin heavy chains indicated that at least one peptide is missing in the maps of the myosins from the external and internal membranes as compared to their soluble counterpart. Our data suggest that myosin is located in three distinct platelet compartments: cytosol, external and internal membranes. The same myosin isoform is located in the two membrane compartments, while the isoform found in the cytosol is different. The observed variations in the structure of the two isoforms may reflect differences in their respective physiological functions.
Insights
Platelets contain distinct myosin isoforms in their cytosol and membranes. This study identified the same myosin isoform in external and internal platelet membranes, differing structurally from the cytoplasmic form, suggesting varied functions.
Area of Science:
- Biochemistry
- Cell Biology
- Hematology
Background:
- Platelets contain at least two myosin isoforms.
- One myosin isoform is membrane-associated, while another is cytoplasmic.
- Previous research characterized structural and functional differences between these myosins.
Purpose of the Study:
- To investigate the localization and characteristics of myosin within platelet membrane subfractions.
- To compare the myosin isoforms found in external and internal platelet membranes with the cytoplasmic isoform.
Main Methods:
- Isolation of external and internal platelet membrane subfractions.
- Characterization of membrane purity using specific marker enzymes.
- Electrophoretic mobility analysis of myosin.
- Two-dimensional peptide mapping of iodinated tryptic peptides of myosin heavy chains.
Main Results:
- Myosin was detected in both external and internal platelet membrane fractions.
- Myosin from both membrane fractions exhibited identical electrophoretic mobility to its cytoplasmic counterpart.
- Two-dimensional peptide mapping revealed structural differences, with at least one peptide missing in membrane-associated myosins compared to the soluble form.
- Data suggest three distinct platelet compartments for myosin: cytosol, external membranes, and internal membranes.
Conclusions:
- A single myosin isoform is present in both external and internal platelet membranes.
- The myosin isoform in platelet membranes is structurally distinct from the cytoplasmic isoform.
- These structural variations likely indicate different physiological roles for the distinct myosin isoforms in platelets.