Cytosolic PAFAH IB is formed of three subunits, alpha (45kD), beta (30kD) and gamma (29kD). The catalytic activity of PAFAH IB resides in the beta and gamma subunits while the alpha subunit has regulatory activity. Trimer formation is not essential for the catalytic activity. Specifically, PAFAH subunit gamma inactivates platelet-activating factor by removing the acetyl group at the sn-2 position. It plays an important role during the development of the brain. In the adult, it is expressed in brain, skeletal muscle, kidney, thymus, spleen, colon, testis, ovary and peripheral blood leukocytes. In the fetus, highest expression occurs in the brain.