HOMONOJIRIMYCIN AND N-METHYL-HOMONOJIRIMYCIN INHIBIT N-LINKED OLIGOSACCHARIDE PROCESSING

Homonojirimycin (HNJ) and N-methylhomonojirimycin (MHNJ) were tested a s inhibitors of the purified glycoprotein processing enzymes, glucosid ase I and glucosidase II. MHNJ was a reasonably good inhibitor of gluc osidase I (K-i = 1 x 10(-6) M) and was about three times as effective on this enzyme as was HNJ, On the other hand, HNJ inhibited glucosidas e II with a K-i of about 1 x 10(-6) M, whereas MHNJ was three times le ss effective (K-i = 3 x 10(-5) M). However, the butyl derivative of HN J had very low activity toward these two processing glucosidases. HNJ and its methyl derivative were also tested in vivo using influenza vir us-infected MDCK cells, and measuring the inhibition of N-linked oligo saccharide processing of the viral envelope glycoproteins. With 100 mu g/ml of MHNJ in the medium, essentially all of the N-linked oligosacc haride chains of the virus were of the ''high-mannose'' type with the major structure being characterized as Glc(3)Man(9)(GlcNAc)(2). Simila r results were obtained with HNJ although this compound was less effec tive in vivo as wed as in vitro. These results are in keeping with the se inhibitors being effective at the glucosidase I step. Both inhibito rs were also tested in MDCK cell cultures to determine whether they af fected the in vivo synthesis of proteins, or of lipid-linked saccharid es. In contrast to deoxynojirimycin, which has been reported to inhibi t the formation of lipid-linked saccharides, no effects were seen on e ither the incorporation of mannose into lipid-linked saccharides or th e incorporation of leucine into protein.