Mammalian phospholipase D: phosphatidylethanolamine as an essential component

Area of Science:

• Biochemistry
• Enzymology
• Cell Biology

Background:

• Phospholipase D (PLD) is a key enzyme involved in phospholipid metabolism.
• Understanding the regulatory factors and substrate specificity of PLD is essential for elucidating its biological roles.

Purpose of the Study:

• To characterize the bovine kidney phospholipase D (PLD) enzyme.
• To identify factors required for PLD activity and determine its substrate preferences.

Main Methods:

• Assay of bovine kidney PLD activity by measuring phosphatidylethanol formation.
• Solubilization and partial purification of particulate PLD using deoxycholate and heparin-Sepharose chromatography.
• Identification of the essential cofactor through extraction and testing of various phospholipids.

Main Results:

• Purified bovine kidney PLD showed minimal activity without an additional factor.
• Phosphatidylethanolamine (PtdEtn), extracted from tissue particulates, was identified as a crucial cofactor.
• Specific forms of PtdEtn and sphingomyelin enhanced PLD activity, while dipalmitoyl-PtdEtn was inactive.
• Mammalian PLD demonstrated selective reactivity with phosphatidylcholine (PtdCho) in mixed micelles or membranes containing PtdEtn.

Conclusions:

• Bovine kidney PLD requires a cofactor, identified as phosphatidylethanolamine (PtdEtn), for optimal enzymatic activity.
• The enzyme preferentially utilizes phosphatidylcholine (PtdCho) as a substrate when presented in a membrane environment with other phospholipids, particularly PtdEtn.
• These findings highlight the importance of lipid context and cofactor availability in regulating mammalian PLD function.