Document Detail

[Identification and characterization of two phospholipase A2 activities in resident mouse peritoneal macrophages.]
MedLine Citation:
PMID:  7316959     Owner:  NLM     Status:  MEDLINE    
Resident mouse peritoneal macrophages synthesize and release large amounts of prostaglandins in response to inflammatory stimuli. Release of prostaglandin E2 and 6-oxoprostaglandin F1 alpha occurs at a rate of 1 nmol/h per mg of cell protein. The mechanisms by which substrate arachidonic acid is released have yet to be established. We have therefore initiated studies to characterize those enzymes that can catalyse its release from phospholipid and may be of significance at the cellular level. We report initially the characterization of two phospholipase A2 activities in homogenates of mouse peritoneal macrophages. The first is active at pH 4.5 and is not dependent on Ca2+. The second is Ca2+-dependent and is optimally active at pH 8.5. Either phospholipase A2 activity is capable of hydrolysing [14C] arachidonic acid from [14C] arachidonic acid-labelled phospholipids in quantities sufficient to account for the amounts of prostaglandins by macrophages in culture. Phospholipid substrates are prepared from mouse LM fibroblasts in serum-free Higuchi medium containing radiolabelled phospholipid precursors. Single-labelled phospholipids bear the 14C label in the arachidonic acid moiety. Dual-labelled phospholipids bear a 14C label in the polar head group and a 3H label in the arachidonic acid moiety. Experiments with dual-labelled substrates establish that both phospholipase activities are of the A2 type as indicated by the equimolar recovery of [3H] arachidonic acid and [14C] lysophospholipid. Studies with aqueous sonicated dispersions of purified [14C] arachidonic acid-labelled phospholipid or mixed liposomal substrates formed from mixtures of cellular polar lipids reveal that the pH 4.5 activity hydrolyses phosphatidylethanolamine and phosphatidylcholine more efficiently when they are present in a mixture of other polar lipids. The pH 8.5 activity, however, hydrolyses the purified phospholipids more efficiently.
P D Wightman; J L Humes; P Davies; R J Bonney
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The Biochemical journal     Volume:  195     ISSN:  0264-6021     ISO Abbreviation:  Biochem. J.     Publication Date:  1981 May 
Date Detail:
Created Date:  1982-02-12     Completed Date:  1982-02-12     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  2984726R     Medline TA:  Biochem J     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  427-33     Citation Subset:  IM    
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MeSH Terms
Arachidonic Acids / metabolism
Ascitic Fluid / cytology,  enzymology*
Calcium / pharmacology
Cells, Cultured
Hydrogen-Ion Concentration
Isoenzymes / metabolism*
Macrophages / drug effects,  enzymology*
Phospholipases / metabolism*
Phospholipases A / metabolism*
Phospholipases A2
Phospholipids / metabolism
Polyethylene Glycols / pharmacology
Reg. No./Substance:
0/Arachidonic Acids; 0/Isoenzymes; 0/Phospholipids; 0/Polyethylene Glycols; 7440-70-2/Calcium; EC 3.1.-/Phospholipases; EC 3.1.1.-/Phospholipases A; EC A2

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