| Abstract: | In the present studies, we have made several unique observations. First, we have shown that cytosolic phosphatidate phosphohydrolase from adipose tissue subjected to butyl-agarose chromatography was resolved into four different components. These components, designated as passthrough (PT), D150, D250 and E, were present in the proportions of 51:7:24:16, respectively, in the rat adipose cytosol. Comparison of the properties of these components revealed some similar properties, and also several differences. These components showed the same pH optimum, required Mg2+ for activity and were inhibited by N-ethylmaleimide, indicating a requirement of active sulfhydryl groups for activity. These components differed from one another with respect to hydrophobicity, sedimentation behavior, Stokes diameter, Km values, thermolability and susceptibility to proteinase treatment. Second, we have shown that each component of this system was associated with lipids which were found to be essential for the catalytic activity. Perturbation of this association by organic solvent or by adding excess amounts of exogenous lipids resulted in the loss of enzyme activity. Finally, we analyzed lipid composition of individual components. These studies suggest that the multi-component system of Mg2+-dependent phosphatidate phosphohydrolase may be a part of the cytomembrane network. |
