We have obtained Chinese hamster ovary cell mutants defective in the biosynthesis of glycosaminoglycans by screening replicate colonies immobilized on polyester cloth. Depending upon the strain, the mutants accumulated less 35S-labeled glycosaminoglycans per ,ug of cell protein by a

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Inhibitors of glycosylation provide a tool for studying the biology of glycoconjugates. Another class of inhibitors consists of glycosides that resemble biosynthetic intermediates involved in glycoconjugate assembly. These compounds act as substrates and produce free oligosaccharides, diverting the assembly of chains from glycoconjugates to the added acceptors. The first type of inhibitor in this class was described >20 years ago by Okayama et aL (7).They showed that f3-D-xylosides stimulate the synthesis of free glycosaminoglycan (GAG) chains and competitively inhibit GAG formation on proteoglycan core proteins (7). The free GAG chains can have desirable biological properties as well. For example, heparan sulfate chains produced on Xyl,3-0-2-naphthol (naphthol-o3-D-xyloside)t will bind to basic fibroblastThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. growth factor, facilitating its interaction with high-affinity receptors (8,9). Recent studies have shown that f3-D-xylosides will prime ganglioside GM3-like compounds and partially I inhibit glycolipid biosynthesis (10). In a similar way, GalNAca-O-benzyl stimulates mucin oligosaccharide synthesis and inhibits 0-linked glycoprotein synthesis (11, 12). Altering glycoprotein synthesis in HL-60 cells in this way inhibits the I expression of sialyl Lewis X [sLex; NeuAca2-*3Gal1,1--> 4(Fuca1->3)GlcNAc-] ligands and adhesion to activated endothelial cells (13).Acceptors consisting of two or more sugars would make this strategy more useful and selective since many glycosyltransferases prefer disaccharides or larger oligosaccharides as substrates (4-6). However, poor transfer of disaccharides across cell membranes severely limits this approach. In this report, we show that decreasing the number of free hydroxyl groups to <5 solves the uptake problem for disaccharides linked to 2-naphthol. Acetylation of the sugars also allows disaccharides to enter the Golgi and prime oligosaccharide chains. MATERIALS AND METHODSSynthesis of Glycosides. The syntheses of Xylp3-0-2-naphthol and L-Araa-0-2-naphthol have been described (8). Gal/3-O-9-phenanthrol, Gal,Bl->3Galf3-O-9-phenanthrol, Gal3l --3Gal3-0-2-naphthol, and Galf3 -4Xyl,B-0-2-naphthol were prepared by reacting the bromo sugar with the sodium salt of the alcohol (A.K.S. and J.D.E., unpublished results). XylJ31-*6Galf3-0-2-naphthol was obtained by reacting acetobromoxylose with Gal,3-0-2-naphthol (Sigma) in the presence of silver carbonate (8). The disaccharide intermediate Xyl(Ac)3f31->6Galf3-O-naphthol was partially methylated by reaction with trimethyloxonium tetrafluoroborate in the presence of 2,6-di(tert-butyl)trimethyl pyridine and the acetyl groups were subsequently removed with sodium methoxide (A.K.S. and J.D.E., unpublished results). Gal,1-*4GlcNAc,3-O-naphthalenemethanol was made by coupling acetylated Galf3-S-C2H5 and 3,6-di-O-benzoylGlcNAcf3-O-n...

The genetic and functional basis of phosphoribosylpyrophosphate synthetase (PRS) superactivity associated with purine nucleotide inhibitor-resistance was studied in six families with this X chromosome-linked purine metabolic and neurodevelopmental disorder. Cloning and sequencing of PRS1 and PRS2 cDNAs, derived from fibroblast total RNA of affected male patients by reverse transcription and PCR amplification, demonstrated that each PRS1 cDNA contained a distinctive single base substitution predicting a corresponding amino acid substitution in the PRS1 isoform. Overall, the array of substitutions encompassed a substantial portion of the translated sequence of PRS1 cDNA. Plasmid-mediated expression of variant PRS1 cDNAs in Escherichia coli BL21 (DE3/pLysS) yielded recombinant mutant PRS1s, which, in each case, displayed a pattern and magnitude of purine nucleoside diphosphate inhibitor-resistance comparable to that found in cells of the respective patient. Kinetic analysis of recombinant mutant PRS1s showed that widely dispersed point mutations in the X chromosomelinked PRPSI gene encoding the PRS1 isoform result in alteration of the allosteric mechanisms regulating both enzyme inhibition by purine nucleotides and activation by inorganic phosphate. The functional consequences of these mutations provide a tenable basis for the enhanced production of phosphoribosylpyrophosphate, purine nucleotides, and uric acid that are the biochemical hallmarks of PRS superactivity. (J. Clin.