The existence of a non-lysosomal glucosylceramidase in human cells has been documented (van Weely, S., Brandsma, M., Strijland, A., Tager, J. M., and Aerts, J. M. F. G. (1993) Biochim. Biophys. Acta 1181, 55-62). Hypothetically, the activity of this enzyme, which is localized near the cell surface, may influence ceramidemediated signaling processes. To obtain insight in the physiological importance of the non-lysosomal glucosylceramidase, the availability of specific inhibitors would be helpful. Here we report on the generation of hydrophobic deoxynojirimycin (DNM) derivatives that potently inhibit the enzyme. The inhibitors were designed on the basis of the known features of the non-lysosomal glucosylceramidase and consist of a DNM moiety, an N-alkyl spacer, and a large hydrophobic group that promotes insertion in membranes. In particular, N-(5-adamantane-1-yl-methoxy)pentyl)-DNM is a very powerful inhibitor of the non-lysosomal glucosylceramidase at nanomolar concentrations. At such concentrations, the lysosomal glucocerebrosidase and ␣-glucosidase, the glucosylceramide synthase, and the N-linked glycantrimming ␣-glucosidases of the endoplasmic reticulum are not affected.

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Dealkylation of quaternary ammonium salts by thiolate anions: A model of the cobalaminindependent methionine synthase reaction. Hilhorst, E.; Chen, T.B.R.A.; Iskander, A.S.; Pandit, U.K. Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract: The reactions of thiolate ions derived from thiophenol and homocysteioe with substituted quatemary ammoniom salts result in alkyl tmnsfer from nitrogen to sulfur. A radical mechanism for this tmnsakylation, accounts for the reactivity pattern of the substrate salts. In a model study of the cobalamin-independent methionine synthase reaction, 5,5.6,7-tetramerhyl-5.6;7,8-tetrahydroptcridiniumsalt(25),whichcanbcconsidaedasamodelf~thenaMalUxxEymc 5-CH$-I4-folate (1). was allowed to react with the thiilate of homocysteiae, whereupon the won of m&ion& was observed in good yield. 'These results suggest that in the enzymatic prcnxss the N(S)-CH3 bond may be activated for the methyl transfer step, by uxndination of the N(5) with an electmphde or a proton at the active site.