Phosphatidic acid phosphatase activity in subcellular fractions derived from adult rat type II pneumocytes in primary culture.

The development of a method for the subcellular isolation of lamellar body, microsomal, mitochondrial and cytosolic enriched fractions from the adult rat type II pneumocyte is presented. These fractions were used to investigate the distribution and specificity of phosphatidic acid phosphatase (EC 3.1.3.4). The cytosolic enriched fraction possessed the greatest proportion of total phosphatidic acid phosphatase activity and the highest relative specific activity. The small amounts of phosphatase activity in the lamellar body, microsomal and mitochondrial enriched fractions correlated best with a nonspecific phosphatase activity. 1,2-Disaturated phosphatidic acid served as a slightly better substrate than did 1-saturated, 2-unsaturated phosphatidic acid in the cytosolic enriched fraction. This observation indicates that the de novo pathway could contribute to dipalmitoylphosphatidylcholine synthesis in the rat type II pneumocyte.