Lysosomal acetyltransferase that acetylates the non-reducing terminal alpha-glucosamine residue of intralysosomal heparin or heparan sulfate, converting it into a substrate for luminal alpha-N-acetyl glucosaminidase. {ECO:0000269|PubMed:16960811, ECO:0000269|PubMed:17033958, ECO:0000269|PubMed:19823584, ECO:0000269|PubMed:20650889}. This is the function of HGSNAT (heparan-alpha-glucosaminide N-acetyltransferase, ENSG00000165102).