Abstract
The present study was designed to determine the subcellular distribution of the platelet ( Ca 2+ + Mg 2+ )-ATPase. Human platelets were surface labeled by the periodate-boro[ 3H]hydride method. Plasma membrane vesicles were then isolated to a purity of approx. 90% by a procedure utilizing wheat germ agglutinin affinity chromatography. These membranes were found to be 2.6-fold enriched in surface glycoproteins compared to an unfractionated vesicle fraction and almost 7-fold enriched compared to intact platelets. In contrast, the isolated plasma membranes showed a decreased specific activity of the ( Ca 2+ + Mg 2+ )-ATPase compared to the unfractionated vesicle fraction. This decrease in specific activity was found to be similar to that of an endoplasmic reticulum marker, glucose-6-phosphatase, and to that of a platelet inner membrane marker, phospholipase A 2. We conclude, therefore, that the ( Ca 2+ + Mg 2+ )-ATPase is not located in the platelet plasma membrane but is restricted to membranes of intracellular origin.
Published Version
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