Calcium is sufficient but not necessary for activation of sheep platelet cytosolic phospholipase A2.
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.
Zupan
L A
LA
Molecular and Cellular Cardiovascular Biochemistry Section, Washington University School of Medicine, St. Louis, MO 63110.
Kruszka
K K
KK
Gross
R W
RW
D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology*; D002850:Chromatography, Gel; D004789:Enzyme Activation; D010741:Phospholipases A / Q000097:blood*; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D012756:Sheep; D012965:Sodium Chloride / Q000494:pharmacology
D010743:Phospholipids; D012965:Sodium Chloride; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium