Glycerolipid biosynthesis in rat adipose tissue 12. Properties of Mg2+-dependent and -independent phosphatidate phosphohydrolase.

The properties of Mg2+-dependent and Mg2+-independent phosphatidate phosphohydrolase activities were investigated in different subcellular fractions in rat adipose tissue. Phosphatidate phosphohydrolase activity was measured in the presence of aqueous dispersed phosphatidate as substrate, and the release of inorganic phosphate was taken as a measure of phosphatidate phosphohydrolase activity. The Mg2+-dependent phosphatidate phosphohydrolase was inhibited in the presence of N-methyl- or N-ethylmaleimide, whereas the Mg2+-independent activity was unaffected by these agents. The Mg2+-dependent phosphatidate phosphohydrolase was more sensitive to proteolysis and to high temperature (55 degrees C) compared to the Mg2+-independent enzyme. The Mg2+-dependent phosphatidate phosphohydrolase activity was reduced significantly during aging without any appreciable effects on the Mg2+-independent phosphatidate phosphohydrolase activity. These studies demonstrate that, in addition to Mg2+-dependency, these two forms of phosphatidate phosphohydrolases differ in several respects irrespective of their location in the adipose cell.