Acyl-protein thioesterase 1 (APT1, Lysophospholipase 1) is a member of a family of critical enzymes, lysophospholipases, that act on biological membranes to regulate the multifunctional lysophospholipids. APT1 hydrolyzes fatty acids from S-acylated cysteine residues in proteins such as trimeric G alpha proteins or HRAS. The role of APT1 in regulating lysophospholipids is important because increased levels of lysophospholipids are detected in a variety of diseases, including atherosclerosis and hyperlipidemia (1). Regulated expression of acyl-protein thioesterase by PKC has been suggested to have important implications for signal transduction processes.