Glycoprotein phosphorylation in simple eucaryotic organisms. Identification of UDP-GlcNAc:glycoprotein N-acetylglucosamine-1-phosphotransferase activity and analysis of substrate specificity

UDP-N-acetylglucosamine:glycoprotein N-acetylglucosamine-1-phosphotransferase activity has been identified in both Acanthamoeba castellani and Dictyostelium discoideum. Each of these activities exhibits a different in vitro specificity toward various purified glycoproteins. The N-acetylglucosaminylphosphotransferase of A. castellani is very similar to the mammalian enzyme in that it phosphorylates the lysosomal enzymes cathepsin D and uteroferrin much more efficiently than nonlysosomal glycoproteins and appears to recognize a determinant on the protein portion of these good acceptors. In contrast the D. discoideum enzyme cannot utilize cathepsin D as a good substrate and, although it phosphorylates uteroferrin efficiently, it does not recognize the protein portion of this acceptor. The oligosaccharide of uteroferrin appears to assume a different conformation than the oligosaccharides of other glycoproteins and glycopeptides, as evidenced by its enhanced sensitivity to mannosidase digestion. This conformation, presumably induced by some interaction with the underlying protein, may be reponsible for the specific phosphorylation of uteroferrin by the N-acetylglucosaminylphosphotransferase of D. discoideum.