Abstract
Microsomal phosphatidate (PA) phosphatase (EC 3.1.3.4) from microspore-derived (MD) cultures of Brassica napus L. was characterized based on sensitivity to the thiol-reactive agent, N-ethylmaleimide (NEM) and dependence on magnesium ions. Both membrane-bound and solubilized PA phosphatase from MD embryos of B. napus L. Topas were inhibited by 50% following preincubation with 0.5 mM NEM. The activity of PA phosphatase was also partially dependent on the inclusion of magnesium ions in the assay buffer. The stability properties of solubilized PA phosphatase were compared to solubilized diacylglycerol acyltransferase (EC 2.3.1.20). PA phosphatase was considerably more labile than diacylglycerol acyltransferase during storage at 4°C. Bovine serum albumin, however, increased the stability of PA phosphatase during storage. PA phosphatase activity was resolved into two major fractions by anion-exchange chromatography on Macro-Prep 50Q. The activity of the enzyme in both fractions was partially inhibited following preincubation with NEM. Microsomal PA phosphatase from MD cell suspension cultures of B. napus L. cv Jet Neuf was also partially inhibited by NEM. The results suggest plant tissues, as in mammalian systems, may contain different forms of PA phosphatase involved in both glycerolipid synthesis and signal transduction.
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