The dynamic modification of cytoplasmic and nuclear proteins by O-linked N-acetylglucosamine (O-GlcNAc) addition and removal on serine and threonine residues is catalyzed by OGT, which adds O-GlcNAc, and MGEA5, a glycosidase that removes O-GlcNAc modifications. Cleaves GlcNAc but not GalNAc from glycopeptides. Can use p-nitrophenyl-beta-GlcNAc as substrate but not p-nitrophenyl-beta-GalNAc or p-nitrophenyl-alpha-GlcNAc. Possesses hyaluronidase activity. Acetylates 'Lys-8' of histone H4 and 'Lys-14' of histone H3. Shows highest expression in the brain, placenta and pancreas.