Microsomal phosphatidic acid phosphohydrolase of rat mammary tissue: I. General properties.

The microsomal bound phosphatidic acid phosphohydrolase from lactating rat mammary tissue had a specific activity of six nmoles per mg protein per minute. The optimum pH was 7.0; magnesium at 1.3 mM was required for maximum activity, and at low substrate concentrations magnesium lowered the Km of the enzyme for phosphatidic acid. Diglycerides exerted little effect while diglyceride ether stimulated enzyme activity. Inorganic salts, i.e., potassium phosphate and potassium chloride, enhanced rates of phosphatidic acid hydrolysis under standard assay conditions.