We propose in this application to continue our studies of mammalian phospholipases. In particular, we will investigate in the liver the plasmalemma phospholipase A1 (MGAT), the mitochondrial phospholipase A2 and the lysosomal phospholipases A1 and A2. The long-range goal is to determine their mechanism of action as well as their physiologic function. For this, we will continue work on their isolation, with the goal of obtaining highly purified preparations for studies on their physical-chemical interaction with lipid substrates. Since each has a different function, several approaches will be used to determine their physiologic action. The plasmalemma MGAT will be studied in the purified form as well as in whole hepatocyte suspensions to determine its role in lipoprotein metabolism. The action of the lysosomal phospholipases in host-defense mechanisms will be investigated in alveolar macrophages since these cells are similar to the Kupffer cells of liver. We will relate the activity of the mitochondrial phospholipase to energy production and to a possible role in attachment of outer and inner mitochondrial membranes. The determination of the distribution of these enzymes in major cell types that can be isolated from liver is essential to understanding their physiologic function.