Phosphatidylinositol hydrolysis by human plasma phospholipase D

Area of Science:

• Biochemistry
• Enzymology
• Human Physiology

Background:

• Phospholipase D (PLD) activity hydrolyzing phosphatidylinositol was previously identified in human neutrophil cytosol.
• The presence and characteristics of this specific PLD activity in human plasma remained uncharacterized.

Purpose of the Study:

• To investigate the presence of phosphatidylinositol-hydrolyzing phospholipase D activity in human plasma.
• To characterize the enzymatic properties of this plasma-derived PLD activity.

Main Methods:

• Assessed enzyme activity by measuring free inositol release from phosphatidylinositol.
• Detected phosphatidate formation as an indicator of hydrolytic activity.
• Evaluated transphosphatidylation capacity by measuring phosphatidylethanol formation.

Main Results:

• Phospholipase D activity capable of hydrolyzing phosphatidylinositol was detected in human plasma.
• The plasma enzyme exhibits optimal activity at pH 8.0.
• The enzyme's activity was inhibited by Ethyleneglycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA).

Conclusions:

• Human plasma possesses a distinct phospholipase D activity that targets phosphatidylinositol.
• This plasma PLD shares characteristics with the previously described neutrophil cytosolic enzyme.
• The enzyme's pH optimum and EGTA sensitivity provide insights into its catalytic mechanism and potential physiological roles.