Problems encountered in measuring the activity of phosphatidate phosphohydrolase

Area of Science:

• Biochemistry
• Enzymology
• Rat Liver Metabolism

Background:

• Microsomal phosphatidate phosphohydrolase (PAP) activity is crucial in lipid metabolism.
• Previous assays measuring phosphate release from phosphatidate may be inaccurate due to side reactions.

Purpose of the Study:

• To evaluate the reliability of phosphate production as an assay for rat liver phosphatidate phosphohydrolase.
• To differentiate between microsomal and soluble PAP activity.

Main Methods:

• Enzyme activity assay measuring phosphate release from phosphatidate.
• Analysis of glycerol phosphate formation and hydrolysis under assay conditions.

Main Results:

• Phosphate release from phosphatidate overestimates microsomal PAP activity.
• Glycerol phosphate is formed from phosphatidate deacylation.
• Glycerol phosphate is not hydrolyzed under the assay conditions for soluble PAP.

Conclusions:

• Phosphate production is a reliable assay for soluble phosphatidate phosphohydrolase in rat liver.
• Accurate measurement of PAP activity requires accounting for glycerol phosphate formation.