Scramblase that mediates the translocation of glucosaminylphosphatidylinositol (alpha-D-GlcN-(1-6)-(1,2-diacyl-sn-glycero-3-phospho)-1D-myo-inositol, GlcN-PI) across the endoplasmic reticulum (ER) membrane, from the cytosolic leaflet to the luminal leaflet of the ER membrane, where it participates in the biosynthesis of glycosylphosphatidylinositol (GPI) (PubMed:35344438). GPI is a lipid glycoconjugate involved in post-translational modification of proteins (PubMed:35344438). Can also translocate 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) (phosphatidylinositol or PI), as well as several other phospholipids (1,2-diacyl-sn-glycero-3-phosphocholine, 1,2-diacyl-sn-glycero-3-phosphoethanolamine), and N-acetylglucosaminylphosphatidylinositol (GlcNAc-PI) in vitro (PubMed:35344438).