The Purification and Characterisation of Phosphatidate Phosphatase from Avocado

Abstract

Phosphatidate phosphatase (EC 3.1.3.4) catalyses the dephosphorylation of phosphatidic acid to diacylglycerol prior to the final acylation step of the Kennedy Pathway. Unlike the acyltransferases, phosphatidate phosphatase (PAP) has received very little attention in plant lipid research. PAP appears to be the rate limiting factor in triacylglycerol biosynthesis, and has been shown to be controlled by translocation to and from the endoplasmic reticulum [1]. As well as in triacylglycerol biosynthesis, both phosphatidic acid (PA) and diacylglycerol (DAG) are intermediates for the major phospholipids. Therefore PAP lies at a theoretical branchpoint between triacylglycerol and phospholipid biosyntheses, the production of these two lipid species may be governed by the extent of translocation of PAP within the cell. It remains to be seen whether PAP plays a role in signal transduction as has been suggested in animal systems, where it plays a pivotal role by regulating the amounts of both lipid second messengers, PA and DAG. It has been found that there are several isoforms of PAP in both yeast and animals, these appear to serve the different functions.