Lysosomal glycerophosphocholine phosphodiesterase in Tetrahymena

The purification and characterization of a novel phosphodiesterase (PDE) is presented. The activity was detected in the extracellular medium of Tetrah ymena thermophila cultures, by the release of p-nitrophenol from p-nitrophe nylphosphocholine (PNPPC) with an acidic pH optimum: In cell homogenates, i t is sedimentable, shows a latency similar to that of acid phosphatase and is co-secreted with this enzyme, indicating that it is a lysosomal hydrolas e. PNPPC-PDE was purified to homogeneity from the extracellular medium, yie lding a single band of 58 kD on SDS polyacrylamide gel electrophoresis. It catalyzed the release of glycerol from glycerophosphocholine (GPC) and GPC competitively inhibits degradation of PNPPC. We present further evidence in dicating that the natural substrate for PNPPC-PDE is GPC. Thus, Tetrahymena becomes the first eukaryote in which a lysosomal GPC-PDE is observed. This finding provides a new pathway for the complete breakdown of phosphatidylc holine in a lysosomal medium.