Abstract
Phospholipases A1 and A2 catalyze the hydrolysis of acyl groups of phospholipids at C-1 and C-2, respectively. These phospholipases are important in phospholipid catabolism and the remodeling of the acyl groups of phospholipids. Phospholipase A from hamster heart cytosol was purified by a combination of ion-exchange and gel filtration chromatography. The purity of the enzyme was assessed by nondenaturing polyacrylamide gel electrophoresis, two-dimension polyacrylamide gel electrophoresis, and immunological studies. The purified enzyme exhibited both phospholipase A1 and A2 activities toward phosphatidylcholine and had the ability to hydrolyze the acyl groups of phosphatidylethanolamine. However, the enzyme was not active toward lysophosphatidylcholine, diacylglycerol, or triacylglycerol. By Sepharose 6B chromatography, the molecular weight of the purified enzyme was estimated to be 140,000. Analysis of the purified enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the enzyme was composed of identical Mr 14,000 subunits. At least six subunits in the native enzyme could be cross-linked by dimethyl suberimidate. Both phospholipase A1 and A2 activities showed similar pH profiles, exhibited no absolute requirements for divalent metallic cations, but displayed a high degree of specificity for the acyl groups of phosphatidylcholine at both C-1 and C-2. The Km of phospholipases A1 and A2 for 1-palmitoyl-2-arachidon-ylglycerophosphocholine was found to be identical (0.5 mM).
Highlights
Acyl groups of phospholipids at C-1 and C-2, respec- Phosphatidylcholine is the major phospholipidin the mamtively
Wehave shown in an earlier repor(t7) that lipid catabolism and the remodeling of the acyl groups the majority of the newly formed phosphatidylcholine
Phospholipase A1 catalyzes thehydrolysis of the acyl group of a phosphoglyceride at C-1, whereas phospholipase A2 catalyzes thehydrolysis of the C-2 acyl group [1].The deacylation of phosphoglycerides is thought to be importantfor the catabolism and/or remodeling of the phospholipids in mammalian cells [2]
Summary
Acyl groups of phospholipids at C-1 and C-2, respec- Phosphatidylcholine is the major phospholipidin the mamtively. The purified enzyme exhibited both phospholipase Al and A2 activities toward phosphatidylcholine and had the ability to hydrolyze the acyl groups of phosphatidylethanolamine.
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