Calcium is sufficient but not necessary for activation of sheep platelet cytosolic phospholipase A2 |
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Authors: | L A Zupan K K Kruszka R W Gross |
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Institution: | Molecular and Cellular Cardiovascular Biochemistry Section, Washington University School of Medicine, St. Louis, MO 63110. |
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Abstract: | In this study we demonstrate that: (1) although the major phospholipase A2 present in sheep platelets is activated by calcium ions, it can effectively catalyze hydrolysis of the sn-2 ester linkage in phospholipids in the absence of calcium; (2) expression of calcium-independent phospholipase A2 activity can be induced by NaCl utilizing purified (but not crude) cytosolic enzyme; and (3) calcium-independent phospholipase A2 activity is regulated by a reconstitutable cytosolic protein. Collectively, these results underscore the fundamental catalytic differences between extracellular and intracellular calcium-dependent phospholipases A2 and demonstrate that calcium is sufficient, but not necessary, for the activation of this class of intracellular phospholipases A2. |
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