ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS Vol. 221, No. 2, March, pp. 593-597, 1983 COMMUNICATION Castanospetmine, a Tetrahydroxylated Alkaloid that Inhibits &Glucosidase and p-Glucocerebrosidase RICK SAUL,* JAMES P. CHAMBERS,? RUSSELL J. MOLYNEUX,$ AND ALAN D. ELBEIN* *Depa&nent of Biochemistry, University of T- Health science Center, San Antonio, T- 78,284 ~Department of Pediatrics, University of T- Health solace Center, How&an, T- 77025; and $Natural Proo!ucb Chemistry Research Unit, Western Rep&d Research Center, Agricultural Research Seruice, USDA, Berhdey, Califonia 94710 Received December 7. 1982 Castanospermine (1,6,7&tetrahydroxyoctahydroindolizine) was tested against a va- riety of commercially available glycosidases and found to be a potent inhibitor of almond emulsin P-glucosidase, and also to inhibit fungal &xylosidase. This alkaloid was inactive on yeast a-glucosidase, (Y- or @galactosidase, a-mannosidase, B-N-ace- tylhexosaminidase, @glucuronidase, cY+fucosidase. Fifty-percent inhibition of &glu- cosidase required about 10 pg/ml of castanospermine. The amount of inhibition was uniform throughout the time course, and the inhibition with regard to substrate con- centration (pnitrophenyl-B-D-glucopyranoside) appeared to be of the mixed type. Cas- tanospermine was also a potent inhibitor of 8-glucocerebrosidase when assayed with fibroblast extracts using either a fluorimetric or a radioactive assay. Interestingly enough, castanospermine also inhibited the lysosomal a-glucosidase, and this inhibition required comparable levels of alkaloid to that required for inhibition of /I-glucocere- brosidase. However, a number of other lysosomal glycosidases were not sensitive to castanospermine (i.e., (Y- or /3-galactosidase, (Y-or &mannosidase, (Y- or /3-L-fucosidase, 8-N-acetylhexosaminidase, @glucuronidase). Castanospermine (1,6,7,8-tetrahydroxyoctahydro- indolizine) is an alkaloid of the indolizidine class, first isolated from the seeds of the Australian le- gume, Casta noqw-mum austrak (1). The structure of this compound is shown in Fig. 1. The seeds of this plant are toxic and cause gastrointestinal irritation when eaten by horses and cattle. Castanospermine bears a structural relationship to another indolizi- dine alkaloid, swainsonine, which is also toxic to an- imals and gives rise to symptoms analogous to those of human a-mannosidosis (2). Swainsonine was shown to be a potent inhibitor of lysosomal and jack bean a-mannosidase (3). and was also found to inhibit gly- coprotein processing by preventing the formation of the normal, complex types of oligosaccharides (4,5). In these processing reactions, swainsonine specifi- cally inhibited mannosidase II that removes a-1,3- and a-1,6-linked mannoses from the GlcNAc-Man,- GlcNAq protein, but had no effect on the a-1,2-man- nosidases (6). Because of the structural similarity between caa- tanospermine and swainsonine, we tested castano- spermine on a number of commercially available gly- cosidases. This alkaloid only inhibited almond emul- sin /3-glucosidase, but was without effect on yeast a-glucosidase, jack bean a-mannosidase, liver @-glue- uronidase, liver &galactosidase, coffee bean a-galac- tosidase, kidney p-N-acetylhexosaminidase, or epi- didymis a-L-fucosidase. The alkaloid did show some inhibitory activity toward AspergiUus @-xylosidase. In addition, castanospermine was a potent inhibitor of fibroblast and white blood cell @glucosidase and fi-glucocerebrosidase. This latter activity might ex- plain the toxicity of this compound, since a genetic insufficiency of the latter enzyme is characteristic of Gauche& disease. It will be of interest to determine 593 0003-9861/83/040593-05$03.00/O Copyright Q 1989 by Academic press, Inc. All rights of reproduction in any form reserved