2-acyl-sn-glycero-3-phosphoethanolamine lysophospholipase A2 activity in guinea-pig heart microsomes.
We have recently described a lysophospholipase A2 activity in guinea-pig heart microsomes that hydrolyses 2-acyl-sn-glycero-3-phosphocholine (2-acyl-GPC). The presence of a similar activity that hydrolyses 2-acyl-sn-glycero-3-phosphoethanolamine (2-acyl-GPE) was not known. In this study, a lysophospholipase A2 activity in guinea-pig heart microsomes that hydrolyses 2-acyl-GPE has been characterized. The enzyme did not require Ca2+ for activity and exhibited a high specificity for 2-arachidonoyl-GPE and 2-linoleoyl-GPE over 2-oleoyl-GPE and 2-palmitoyl-GPE. The specificity for these unsaturated substrates was observed in the presence and absence of detergents. Selective hydrolysis of 2-arachidonoyl-GPE over 2-palmitoyl-GPE was observed when equimolar quantities of the two substrates were incubated with the enzyme. There was no preferential hydrolysis of either 2-linoleoyl- or 2-arachidonoyl-GPE when presented individually or as a mixture. Significant differences in the characteristics of 2-acyl-GPE-hydrolysing and 2-acyl-GPC-hydrolysing activities included differences in their optimum pH, the effect of Ca2+ and their acyl specificities. Taken together, these results suggest that the two activities are catalysed by different enzymes. 2-Acyl-GPE lysophospholipase activity with a preference for 2-arachidonoyl-GPE over 2-oleoyl-GPE was observed in guinea-pig brain, liver, kidney and lung microsomes. Lysophospholipase A1 activity that catalyses the hydrolysis of 1-acyl-GPE was also present in guinea-pig heart microsomes and had different characteristics from the 2-acyl-GPE-hydrolysing activity, including a preference for saturated over unsaturated substrates. The 2-acyl-GPE lysophospholipase A2 activity appeared to be distinct from Ca(2+)-independent phospholipase A2. The characteristics of the 2-acyl-GPE lysophospholipase A2 suggest it could play a role in the selective release of arachidonic and linoleic acids for further metabolism in cells.
Badiani
K
K
Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Arthur
G
G
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D006168:Guinea Pigs; D007700:Kinetics; D008245:Lysophospholipase / Q000302:isolation & purification / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology*; D009928:Organ Specificity; D051381:Rats; D013379:Substrate Specificity
D003902:Detergents; C068724:2-acyl-sn-glycero-3-phosphoethanolamine lysophospholipase A2; D008245:Lysophospholipase; D002118:Calcium