Identification and Distribution of Peptide:N-Glycanase (PNGase) in Mouse Organs

A wide occurrence of peptide:N-glycanase (PNGase) in mouse organs was demonstrated. PNGase activities were determined using 14C-labeled fetuin glycopeptide I as a substrate by a newly improved enzyme assay based on the paper chromatographic and paper electrophoretic analyses. PNGase activities were detected in both soluble and membranous (or particulate) fractions, although the levels of the activities were different from organ to organ. Soluble PNGases were partially purified from brain, liver, kidney, and spleen by TSK butyl-Toyopearl 650 M hydrophobicity chromatography and characterized for enzymatic properties. The soluble enzymes were found to share the following properties: (a) high hydrophobicity; (b) sensitivity to metal cations such as Zn2+, Cu2+ and Fe3+; and (c) requirement of sulfhydryl group(s) for enzyme activity. Notably, soluble PNGases were unable to degrade glycoasparagine substrates and the optimal pH was near 7.0, suggesting that they were not lysosomal enzymes, but perhaps being involved in basic biological processes in certain intracellular nonlysosomal events. All of these enzymatic properties found for mouse organ-derived PNGases were the same as those recently found for L-929 PNGase that was highly purified as a soluble enzyme from mouse fibroblast L-929 cells (Suzuki, T., Seko, A., Kitajima, K., Inoue, Y., and Inoue, S. (1994) J. Biol Chem. 269, 17611-17618).