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Biosynthesis of platelet-activating factor. I. Evidence for an acetyl-transferase activity in murine macrophages
Abstract:
Platelet-activating factor (PAF-acether; 1-0-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) is released from murine peritoneal adherent cells by inflammatory and non-inflammatory stimuli. We have found, in extracts from these cells, an enzyme activity that synthesizes. PAF-acether from synthetic lyso-PAF-acether by transferring the acetyl moiety of acetyl-coenzyme A onto the lyso-PAF-acether molecule. The enzyme is stabilized by 1 mM dithiothreitol, is calcium-dependent, has an apparent Km of 172 microM for acetyl-CoA and is active in a 6-8 pH range. When the acetyl-CoA substrate is replaced by propionyl-CoA, an ether lipid is produced which turns out to be as potent an aggregating agent as PAF-acether. In all cases, the products of the reaction were characterized by their behaviour in platelet-aggregation tests and their high-pressure liquid chromatography (HPLC) elution profiles. The precise definition of this acetyl-transferase is of primary importance for the development of new pharmacological agents capable of moduling a potent platelet aggregating factor.
Insights
Researchers discovered an enzyme that synthesizes platelet-activating factor (PAF) from lyso-PAF. This enzyme
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Platelet-activating factor (PAF-acether) is a potent lipid mediator released from various cells.
- Understanding PAF synthesis is crucial for developing targeted therapies.
Purpose of the Study:
- To identify and characterize the enzyme responsible for PAF synthesis in murine peritoneal adherent cells.
- To investigate the enzyme's substrate specificity and optimal reaction conditions.
Main Methods:
- Enzyme assays using synthetic lyso-PAF-acether and acetyl-CoA as substrates.
- Characterization of enzyme activity, including dependence on calcium and pH.
- Analysis of reaction products using platelet aggregation tests and HPLC.
Main Results:
- An acetyl-transferase activity was identified in cell extracts, synthesizing PAF from lyso-PAF and acetyl-CoA.
- The enzyme is calcium-dependent, with optimal activity in a pH range of 6-8.
- Replacing acetyl-CoA with propionyl-CoA produced a potent ether lipid aggregating agent.
Conclusions:
- A novel acetyl-transferase enzyme plays a key role in PAF biosynthesis.
- This enzyme represents a potential target for pharmacological intervention in PAF-mediated conditions.
- Further characterization is essential for developing modulators of this potent platelet aggregating factor.