Lipin proteins LPIN1, 2, and 3, associated with the endoplasmic reticulum membrane, can each catalyze the hydrolysis of phosphatidate to yield 1,2-diacyl-glycerol and orthophosphate. The activities of LPIN1 and LPIN2 have been established experimentally (Grimsey et al. 2008); that of LPIN3 is inferred from its structural similarities both to its human paralogues and to its mouse ortholog (Donkor et al. 2007). Only LPIN1 has been shown to be stably associated with the endoplasmic reticulum, but all three enzymes appear to be catalytically active at that location (Grimsey et al. 2008; Donkor et al. 2007).