[Isoform 1]: Cleaves GlcNAc but not GalNAc from O- glycosylated proteins (PubMed:11148210, PubMed:11788610, PubMed:20673219, PubMed:22365600, PubMed:24088714, PubMed:28939839, PubMed:37962578). Deglycosylates a large and diverse number of proteins, such as CRYAB, ELK1, GSDMD, LMNB1 and TAB1 (PubMed:28939839, PubMed:37962578). Can use p-nitrophenyl-beta-GlcNAc and 4- methylumbelliferone-GlcNAc as substrates but not p-nitrophenyl-beta- GalNAc or p-nitrophenyl-alpha-GlcNAc (in vitro) (PubMed:20673219). Does not bind acetyl-CoA and does not have histone acetyltransferase activity (PubMed:24088714). {ECO:0000269|PubMed:11148210, ECO:0000269|PubMed:11788610, ECO:0000269|PubMed:20673219, ECO:0000269|PubMed:22365600, ECO:0000269|PubMed:24088714, ECO:0000269|PubMed:28939839, ECO:0000269|PubMed:37962578}. [Isoform 3]: Cleaves GlcNAc but not GalNAc from O- glycosylated proteins. Can use p-nitrophenyl-beta-GlcNAc as substrate but not p-nitrophenyl-beta-GalNAc or p-nitrophenyl-alpha-GlcNAc (in vitro), but has about six times lower specific activity than isoform 1. . This is the function of OGA (O-GlcNAcase, Ensembl gene identifier ENSG00000198408).