* GNPTAB is the catalytic unit of the N-acetylglucosamine-1-phosphotransferase complex that attaches the mannose 6-phosphate (M6P) marker to selected high mannose type oligosaccharides in the Golgi. This modification occurs on acid hydrolases. This helps target these lysosomal enzymes to the endosomal/prelysosomal compartment via M6P receptors (MPR) mediated vesicular transport.
* GNPTG is the non-catalytic subunit that forms a complex with GNPTAB.