Role of acidic Ca2+-independent phospholipase A2 in synthesis of lung dipalmitoyl phosphatidylcholine.
Dipalmitoyl phosphatidylcholine (deltaPC) synthesis by lung epithelium occurs in part by a deacylation/reacylation pathway utilizing phospholipase A2 (PLA2) and an acyl transferase. The role of acidic Ca2+-independent PLA2 (aiPLA2) in this pathway was investigated using a transition-state analog enzyme inhibitor [1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33)]. Granular pneumocytes were isolated from rat lung with elastase and were maintained in primary culture for 24 h on microporous membranes in the presence of radiolabeled choline or free fatty acids (palmitate plus oleate). Disaturated phosphatidylcholine (DSPC) was determined by osmication chromatography. Incorporation (nmol/mg protein) into DSPC at 24 h incubation was 11.9 +/- 0.2 for [3H]choline and 12.1 +/- 0.04 for [3H]palmitate. In the presence of 3 mol% MJ33, incorporation of [3H] choline and [3H]palmitate was decreased by 37 and 69%, respectively, and DSPC pool size (microg/mg cell protein) decreased by 9% (P < 0.05). A similar decrease in radiolabel incorporation was observed with 2 h of incubation. The presence of p-bromophenacyl bromide (20 microm) had a significantly smaller effect that was additive with that of MJ33. After 24 h of labeling and 4 h of chase with unlabeled substrate, there was a significant decrease of radiolabel in DSPC that was inhibited by MJ33. Under all experimental conditions, MJ33 resulted in either no change or a modest increase of radiolabel in the cellular unsaturated PC fraction. These results indicate that aiPLA2 has a major role in DSPC synthesis by granular pneumocytes.
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Institute for Environmental Medicine, University of Pennsylvania Medical Center, Philadelphia 19104, USA.
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D015060:1,2-Dipalmitoylphosphatidylcholine / Q000096:biosynthesis*; D000143:Acids / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005227:Fatty Acids / Q000494:pharmacology; D005994:Glycerophosphates / Q000494:pharmacology; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008744:Methylamines / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000502:physiology*; D054467:Phospholipases A2; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity
D000143:Acids; D004791:Enzyme Inhibitors; D005227:Fatty Acids; D005994:Glycerophosphates; D008744:Methylamines; C078587:1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol; D015060:1,2-Dipalmitoylphosphatidylcholine; C027451:methylamine; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium