On the mechanism of lysophospholipase activity of secretory phospholipase A2 (EC 3.1.1.4): deacylation of monoacylphosphoglycerides by intrinsic sn-1 specificity and pH-dependent acyl migration in combination with sn-2 specificity.
We show for the first time that secreted low-molecular weight phospholipase A2 (EC 3.1.1.4) catalyzes the deacylation of monoacylphosphoglycerides directly from the sn-1 position, although at a very low rate: purified phospholipase A2 enzymes from bee venom, crotalus atrox venom, and porcine pancreas hydrolyze the sn-1 ester bond in 1-palmitoyl-2-O-methyl-sn-glycero-3-phosphorylcholine. Hydrolytic rates with the corresponding isomer, 1-O-methyl-2-palmitoyl-sn-glycero-3-phosphorylcholine, are about 3-4 orders of magnitude higher. The similarities in Ca2+ requirement and inactivation profiles suggest that deacylation, albeit with different rates, from both sn-1 and sn-2 positions is catalyzed by the same catalytic site of phospholipase A2. Furthermore, evidence is provided that phospholipase A2-catalyzed 1-acyl lysophospholipid deacylation is mediated by sn-1-directed action, but above pH 7 acyl migration with subsequent enzyme-catalyzed hydrolytic cleavage from the sn-2 position contributes to the overall deacylation of monoacylphosphoglycerides, acyl migration becoming eventually the rate-limiting factor.
Kunze
H
H
Max-Planck-Institut für Experimentelle Medizin, Göttingen, Germany. kunze@mpiem.gwdg.de
Bohn
E
E
Eibl
H
H
D000215:Acylation; D005994:Glycerophosphates / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008245:Lysophospholipase / Q000302:isolation & purification / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010741:Phospholipases A / Q000302:isolation & purification / Q000378:metabolism*; D054467:Phospholipases A2; D014688:Venoms / Q000201:enzymology
D005994:Glycerophosphates; D010713:Phosphatidylcholines; D014688:Venoms; D010741:Phospholipases A; D054467:Phospholipases A2; D008245:Lysophospholipase