Identification of N-acetylglucosamine-alpha-1-phosphate transferase activity in Dictyostelium discoideum: an enzyme that initiates phosphoglycosylation.

A lysosomal proteinase from Dictyostelium discoideum was previously shown to have GlcNAc alpha-1-P residues in phosphodiester linkage to serine. We have identified a GlcNAc-alpha-1-P transferase activity in membrane preparations using UDP[3H]GlcNAc and a peptide acceptor with three tandem Ser-Gly repeats. We established an assay, proved the structure of the product, determined the Kms for donor and acceptor and showed that the glycopeptide binds a GlcNAc-alpha-1-P specific rabbit antibody. These findings provide the tools to search for mutants lacking GlcNAc-alpha-1-P transferase activity as a probe for the function of this modification we call phosphoglycosylation.