Alpha1 catalytic subunit of the cytosolic type I platelet-activating factor (PAF) acetylhydrolase (PAF-AH (I)) heterotetrameric enzyme that catalyzes the hydrolyze of the acetyl group at the sn-2 position of PAF and its analogs and modulates the action of PAF. The activity and substrate specificity of PAF-AH (I) are affected by its subunit composition. Both alpha1/alpha1 homodimer (PAFAH1B3/PAFAH1B3 homodimer) and alpha1/alpha2 heterodimer(PAFAH1B3/PAFAH1B2 heterodimer) hydrolyze 1-O-alkyl-2-acetyl-sn-glycero-3-phosphoric acid (AAGPA) more efficiently than PAF, but they have little hydrolytic activity towards 1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylethanolamine (AAGPE). Plays an important role during the development of brain. a 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine + H2O = 1-O-alkyl-sn-glycero-3-phosphocholine + acetate + H(+) 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine + H2O = 1-O-hexadecyl-sn-glycero-3-phosphocholine + acetate + H(+) 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphate + H2O = 1-O-hexadecyl-sn-glycero-3-phosphate + acetate + H(+) Beta subunit (PAFAH1B1) inhibits the acetylhydrolase activity of the alpha1/alpha1 catalytic homodimer. Forms a catalytic dimer which is either homodimer (alpha1/alpha1 homodimer) or heterodimer with PAFAH1B2 (alpha1/alpha2 heterodimer). Component of the cytosolic (PAF-AH (I)) heterotetrameric enzyme, which is composed of PAFAH1B1 (beta), PAFAH1B2 (alpha2) and PAFAH1B3 (alpha1) subunits. The catalytic activity of the enzyme resides in the alpha1 (PAFAH1B3) and alpha2 (PAFAH1B2) subunits, whereas the beta subunit (PAFAH1B1) has regulatory activity. Trimer formation is not essential for the catalytic activity (By similarity). Interacts with VLDLR; this interaction may modulate the Reelin pathway (PubMed:17330141). Expressed already by the time of neurulation. By 10.5 dpc, expression is abundant in the developing central and peripheral nervous systems. Major sites include the neuroepithelium of the fore-, mid-, and hindbrain, the spinal cord, the dorsal root, and cranial ganglia. In adult brain, expression is greatly diminished. Knockout mice which are homozygous for the PAFAH1B2 gene appear developmentally normal, and are born at the expected Mendelian rate. Mice have normal fertility and normal spermatogenesis. Double mutant female mice which are homozygous for PAFAH1B2 and PAFAH1B3 are grossly normal and fertile, whereas double-mutant males are infertile. Double mutan mice manifest an earlier disturbance of spermatogenesis with an onset at preleptotene or leptotene stages of meiosis. Originally the subunits of the type I platelet-activating factor (PAF) acetylhydrolase was named alpha (PAFAH1B1), beta (PAFAH1B2) and gamma (PAFAH1B3) (By similarity). Now these subunits have been renamed beta (PAFAH1B1), alpha2 (PAFAH1B2) and alpha1 (PAFAH1B3) respectively (By similarity). Belongs to the 'GDSL' lipolytic enzyme family. Platelet-activating factor acetylhydrolase IB beta/gamma subunits subfamily.