Characteristics of Cytosolic Calcium-Independent Phospholipase $A_2$ Isolated from Rat Liver

  • Won, Jong-Hak (Department of Biology, College of Natural Science, Sungkyunkwan University) ;
  • Na, Doe-Sun (Department of Biochemistry, College of Medicine, University of Ulsan) ;
  • Rhee, Hae-Jin (Department of Biochemistry, College of Medicine, University of Ulsan) ;
  • Park, Young-Min (Department of Biology, College of Natural Science, Sungkyunkwan University)
  • Received : 1998.11.06
  • Accepted : 1998.11.24
  • Published : 1999.03.31

Abstract

A calcium-independent phospholipase $A_2$ ($iPLA_2$) was identified from the cytosolic fraction of rat liver cells. On gel filtration chromatography, the $iPLA_2$ activity was eluted as broad peaks of 150 to 500 kDa. The enzyme was maximally active at pH 7.5, retained 75% of its original activity after heating at $50^{\circ}C$ for 5 h, and was inhibited by $Ca^{2+}$, $Mg^{2+}$, and $Zn^{2+}$ ions, but was not affected by $Na^+$ and $K^+$ ions. The enzymatic activity was increased up to 150% by 1 to 4 mM DTT and was inhibited up to 25% by 0.1 to 1 mM PMSF. The $iPLA_2$ activity had preference for the head group of phospholipids, where phosphatidylethanolamine was preferred to phosphatidylcholine. The results suggest that the $iPLA_2$ may be a novel enzyme distinct from the previously reported $iPLA_2s$.

Keywords

$Ca^{2+}$-independen $PLA_2$;Enzyme activity;Rat liver