Colorimetric determination of pure Mg²⁺-dependent phosphatidate phosphatase activity

The malachite green-molybdate reagent was used for a colorimetric assay of pure Mg2⁺-dependent phosphatidate phosphatase activity. This enzyme plays a major role in fat metabolism. Enzyme activity was linear with time and protein concentration, and with the concentration of water-soluble dioctanoyl phosphatidate. The colorimetric assay was used to examine enzyme inhibition by phenylglyoxal, propranolol, and dimethyl sulfoxide. Pure enzyme and a water-soluble phosphatidate substrate were required for the assay, which should be applicable to a well-defined large-scale screen of Mg2⁺-dependent phosphatidate phosphatise inhibitors (or activators).