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Monoglyceride and diglyceride lipases from human platelet microsomes
1Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Kentucky, Lexington 405367-0082.
Biochimica Et Biophysica Acta
|December 16, 1988
Summary
Diglyceride lipase and monoglyceride lipase roles in human platelet arachidonate release were characterized. Diglyceride lipase activity is the rate-limiting step, despite monoglyceride lipase having higher specific activity.
Area of Science:
- Biochemistry
- Enzymology
- Platelet Biology
Background:
- Human platelets release arachidonate, a key signaling molecule, through enzymatic pathways.
- Diglyceride lipase (lipoprotein lipase, EC 3.1.1.24) and monoglyceride lipases (acylglycerol lipase, EC 3.1.1.23) are implicated in lipid metabolism.
Purpose of the Study:
- To characterize the properties of diglyceride lipase and monoglyceride lipase.
- To assess their roles in arachidonate release from activated human platelets.
Main Methods:
- Enzyme activity assays at varying pH.
- Inhibition studies with metal ions (EDTA, Ca2+, Mg2+, Mn2+, Hg2+, Cu2+) and sulfhydryl inhibitors.
- Assessment of inhibition by antiplatelet drugs.
- Kinetic analysis (Km values) and specific activity comparisons.
Main Results:
- Diglyceride lipase optimal activity at pH 3.5; monoglyceride lipase at pH 7.0.
- Both enzymes inhibited by Hg2+ and Cu2+, suggesting sulfhydryl group involvement.
- Monoglyceride lipase more susceptible to sulfhydryl inhibitors.
- Both lipases inhibited by antiplatelet drugs.
- Comparable Km values for diglyceride lipase and diglyceride kinase suggest concurrent metabolism.
- Monoglyceride lipase specific activity is >100-fold higher than diglyceride lipase.
Conclusions:
- Diglyceride lipase activity is the rate-limiting step in arachidonate release.
- Enzyme properties and inhibition profiles provide insights into platelet activation pathways.
- Characterization aids understanding of lipid mediator generation in platelets.