A review of phosphatidate phosphatase assays

Phosphatidate phosphatase (PAP) catalyzes the penultimate step in the synthesis of triacylglycerol and regulates the synthesis of membrane phospholipids. There is much interest in this enzyme because it controls the cellular levels of its substrate, phosphatidate (PA), and product, DAG; defects in the metabolism of these lipid intermediates are the basis for lipid-based diseases such as obesity, lipodystrophy, and inflammation. The measurement of PAP activity is required for studies aimed at understanding its mechanisms of action, how it is regulated, and for screening its activators and/or inhibitors. Enzyme activity is determined through the use of radioactive and nonradioactive assays that measure the product, DAG, or Pi However, sensitivity and ease of use are variable across these methods. This review summarizes approaches to synthesize radioactive PA, to analyze radioactive and nonradioactive products, DAG and Pi, and discusses the advantages and disadvantages of each PAP assay.

Cold stress affects H+-ATPase and phospholipase D activity in Arabidopsis

Low temperature is an environmental stress that greatly influences plant performance and distribution. Plants exposed to cold stress exhibit modifications of plasma membrane physical properties that can affect their functionality. Here it is reported the effect of low temperature exposure of Arabidopsis plants on the activity of phospholipase D and H⁺-ATPase, the master enzyme located at the plasma membrane. The H⁺-ATPase activity was differently affected, depending on the length of cold stress imposed. In particular, an exposure to 4 °C for 6 h determined the strong inhibition of the H⁺-ATPase activity, that correlates with a reduced association with the regulatory 14-3-3 proteins. A longer exposure first caused the full recovery of the enzymatic activity followed by a significant activation, in accordance with both the increased association with 14-3-3 proteins and induction of H⁺-ATPase gene transcription. Different time lengths of cold stress treatment were also shown to strongly stimulate the phospholipase D activity and affect the phosphatidic acid levels of the plasma membranes. Our results suggest a functional correlation between the activity of phospholipase D and H⁺-ATPase mediated by phosphatidic acid release during the cold stress response.

Involvement of phosphatidate phosphatase in the biosynthesis of triacylglycerols in Chlamydomonas reinhardtii

Lipid biosynthesis is essential for eukaryotic cells, but the mechanisms of the process in microalgae remain poorly understood. Phosphatidic acid phosphohydrolase or 3-sn-phosphatidate phosphohydrolase (PAP) catalyzes the dephosphorylation of phosphatidic acid to form diacylglycerols and inorganic orthophosphates. This reaction is integral in the synthesis of triacylglycerols. In this study, the mRNA level of the PAP isoform CrPAP2 in a species of Chlamydomonas was found to increase in nitrogen-free conditions. Silencing of the CrPAP2 gene using RNA interference resulted in the decline of lipid content by 2.4%-17.4%. By contrast, over-expression of the CrPAP2 gene resulted in an increase in lipid content by 7.5%-21.8%. These observations indicate that regulation of the CrPAP2 gene can control the lipid content of the algal cells. In vitro CrPAP2 enzyme activity assay indicated that the cloned CrPAP2 gene exhibited biological activities.