Abstract
The malachite green-molybdate reagent was used for a colorimetric assay of pure Mg
2+
-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 Mg
2+
-dependent phosphatidate phosphatase inhibitors (or activators).