The substrate specificity of brain microsomal phospholipase D

Area of Science:

• Biochemistry
• Enzymology
• Neuroscience

Background:

• Phospholipase D (PLD) is an enzyme activated by neurotransmitters.
• PLD is known to hydrolyze phosphatidylcholine and exhibits transphosphatidylation.
• Understanding PLD's substrate specificity is crucial for its biological roles.

Purpose of the Study:

• To develop and validate a novel in vitro assay for studying phospholipase D.
• To investigate the substrate specificity of rat brain microsomal phospholipase D.
• To characterize the optimal conditions for PLD activity in the developed assay.

Main Methods:

• Utilized an in vitro assay with [3H]butanol as a nucleophilic acceptor.
• Employed a microsomal membrane fraction from rat brain as the enzyme source.
• Analyzed product formation (phosphatidyl[3H]butanol) using thin-layer chromatography (t.l.c.).
• Varied detergent (sodium oleate) concentrations to determine optimal activity.

Main Results:

• Successfully synthesized and identified phosphatidyl[3H]butanol using the novel assay.
• Phospholipase D activity was detergent-dependent, with optimal sodium oleate concentration between 4-6 mM.
• Rat brain PLD demonstrated highest activity towards phosphatidylcholine, with lower activity against phosphatidylethanolamine and phosphatidylserine.
• No significant activity was observed against phosphatidylinositol.
• Substrate preference correlated with head-group similarity to choline; fatty acid composition was not a determining factor.

Conclusions:

• The developed [3H]butanol assay is a valuable tool for studying phospholipase D without the need for labeled substrate.
• Rat brain phospholipase D exhibits specific substrate preferences, primarily hydrolyzing phosphatidylcholine.
• This research provides insights into the enzymatic properties and substrate specificity of phospholipase D, aiding further investigation.