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 ceramide-mediated 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 α-glucosidase, the glucosylceramide synthase, and the N-linked glycantrimming α-glucosidases of the endoplasmic reticulum are not affected.
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