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PubMed1971

5-hydroxytryptamine metabolism in sheep.

1. 5-Hydroxytryptamine (5-HT) (10 mg) administered intravenously to sheep was mostly excreted in the urine as 5-HT-O-glucuronide (705+/-162 mug, mean from six wethers+/-S.E.M.) and 5-hydroxyindolylacetic acid (5-HIAA) (6,850+/-1,538 mug). Oral administration of 5-HT (100 mg) led to the excretion of 590+/-212 mug 5-HT-O-glucuronide (mean from five wethers+/-S.E.M.) and 7,394+/-2,093 mug 5-HIAA in the urine.2. After administration of DL-5-hydroxytryptophan (DL-5-HTP) (20 mg i.v. or 200 mg orally) sheep excreted about 5 mg 5-HT in the urine together with 5-HT-O-glucuronide and 5-HIAA. The excretion of 5-HT suggests that some DL-5-HTP perfused the liver and the lungs before being decarboxylated.3. Twenty-four hour specimens of control urine contained 335+/-45 mug 5-HT, 909+/-90 mug 5-HT-O-glucuronide and 3,352+/-362 mug 5-HIAA (seven sheep in each instance). Thus endogenous 5-HT seemed to be conjugated with glucuronic acid to a greater extent than administered 5-HT.4. Although urinary 5-HIAA was reduced after a single dose of isocarboxazid (20 mg/kg daily) the 5-HT-O-glucuronide content of the specimens was not increased until two or three doses of the drug had been given.5. Carbon tetrachloride (4 ml orally) reduced the urinary excretion of 5-HT-O-glucuronide. Although the conjugation of 5-HT with glucuronic acid was inhibited after administration of carbon tetrachloride the excretion of 5-HT and 5-HIAA was not increased. This observation suggests that carbon tetrachloride impaired the formation or clearance of endogenous 5-HT in sheep.

5-Hydroxytryptophan↗
PubMed1988

Short-chain fatty acid production from mono- and disaccharides in a fecal incubation system: implications for colonic fermentation of dietary fiber in humans.

An in vitro fecal incubation system was used to demonstrate how lactose, lactulose and monosaccharides (mainly constituents of dietary fiber) influence short-chain fatty acid production in colon. Short-chain fatty acids were formed from all mono- and disaccharides tested (except L-glucose): D-glucose, D-galactose, D-fructose, D-mannose, L-rhamnose, D-sorbitol, D-arabinose, D-xylose, D-ribose, D-galacturonate, D-glucuronate, lactose and lactulose. All saccharides increased acetate formation; propionate production was increased from rhamnose, arabinose, xylose, ribose, galacturonic and glucuronic acid, whereas the synthesis of butyrate was elevated in assays incubated with sorbitol, galacturonic and glucuronic acid, and to a lesser degree ribose. Isobutyrate, valerate, isovalerate and hexanoate were produced in increased amounts in assays incubated with albumin, but in fact decreased in many incubations with saccharides. It is speculated that saccharide fermentation always results in formation of acetate, and that the relative production of acetate, propionate and butyrate is related to the monosaccharide composition of dietary fiber available for colonic bacteria. However, the production of isobutyrate, valerate, isovalerate and hexanoate is probably not due to saccharide fermentation, but is rather of polypeptide origin.

Acetates↗
PubMed1976

The isolation and characterization of bilirubin diglucuronide, the major bilirubin conjugate in dog and human bile.

The chemical structure of the major conjugate of bilirubin was unequivocally elucidated by structural analysis. The conjugated bilirubins were first separated from the lipid components of human duodenal aspirates or dog gall-bladder bile, and then resolved by t.l.c. into a series of tetrapyrroles. The major tetrapyrrole was then converted into its more stable dipyrrolic azo derivative for further analysis. The conjugated moiety of the azopigment was characterized after methanolysis with sodium methoxide. This reaction yields two types of product, those soluble in water and those soluble in organic solvents. The organic-soluble fraction was shown by t.l.c. and mass spectrometry to contain the methyl esters of the dipyrrolic azo derivatives of bilirubin. The water-soluble materials were analysed by enzymic procedures, t.l.c., n.m.r. spectrometry and combined g.l.c. and mass spectrometry. This analysis showed that the only water-soluble product resulting from the methanolysis was glucuronic acid. The structure was identical with that of pure standards, on both mass spectrometry and n.m.r. spectroscopy. No contaminating moieties were found. Quantitative measurement indicated that the glucuronic acid had been released in a 1:1 molar ratio with the resulting methyl esters of the dipyrrolic azo derivatives of bilirubin. This unequivocally establishes bilirubin diglucuronide as the major pigment present in bile. Past problems with identification of bilirubin diglucuronide were shown to originate from procedures which resulted in incomplete separation and isolation of the azopigments of the conjugated bilirubins, owing to contamination by biliary lipids.

Animals↗
PubMed1978

Drug metabolism in a case of progeria.

A case of premature ageing (progeria) in a 3-year-old Indian child is described. The conjugations of paracetamol with glucuronic acid and sulphate, of benzoic acid with glycine and of phenylacetic acid with glutamine have been investigated in this child, in view of suggestions that these reactions are impaired in old age. The results suggest that the glucuronic acid conjugation pathway may be quantitatively less important in the progeric child than in normal children and adults.

Acetaminophen↗
PubMed1986

Structural analysis of papaya polysaccharide II.

The structure of papaya polysaccharide II (PP II) isolated by Chandrasekaran et al. [Carbohydr. Res., 60 (1978) 105-115] has been investigated by methylation analysis of the carboxyl-reduced polymer and by partial hydrolysis of both the intact (arabinose, 31.0; rhamnose, 13.3; galactose, 42.6; glucuronic acid, 10.3; and 4-O-methylglucuronic acid, 2.8%), and carboxyl-reduced polymers. Methylation analysis of carboxyl-reduced PP II indicated a very highly branched structure in which approximately 39% of the galactopyranose units are disubstituted, 24% are monosubstituted, 20% are trisubstituted, and 17% are nonreducing end units. Methylation analysis of products of partial hydrolysis of both intact and carboxyl-reduced polymers indicated that the backbone of the polysaccharide is made up of galactosyl residues substituted at either O-3 or -6, that the principal aldobiouronic acid fragment is 6-O-(glucopyranosyluronic acid)galactose, that the rhamnosyl units are substituted at O-3 with either terminal arabinofuranosyl or galactopyranosyl groups, and that the rhamnosyl residues are themselves linked to glucuronic acid residues through O-4. From this information, a possible statistical fragment with six arabinofuranose and two galactopyranose nonreducing end-groups per 19 sugar units [five units in the main chain of (1----3)-linked galactopyranose units] is proposed.

Carbohydrate Conformation↗
PubMed2004

Inhibitory activities of sulfated proteoglycans on chondroitin sulfate A-mediated cytoadherence of Plasmodium falciparum isolates from Thailand.

Chondroitin sulfate A (CSA) is an important receptor for Plasmodium falciparum-infected erythrocytes in the placenta. To study the molecular interaction between parasitized erythrocytes (PE) to CSA, we performed in vitro cytoadherence inhibition assays of PE infected with wild and laboratory isolates of P. falciparum to CSA using various glycosaminoglycans (GAGs). Marked decrease in PE adhesion to immobilized CSA and CSA-expressed cells was achieved with soluble chondroitin sulfate D (CSD) and chondroitin sulfate E (CSE) at low concentrations. The effect was dose dependent with the degree of inhibition exceeded that of soluble CSA in certain clinical isolates. The results suggested the influence of oversulfation of CS variant chains on PE adherence to CSA. Interestingly, PE of the tested wild isolates could adhere to immobilized CSD and CSE at different levels while PE of CSA-selected laboratory lines could not. Partial inhibitory activity was observed when chondroitin sulfate C (CSC), chondroitin sulfate B (CSB), and polyolpolysulfate were used even at high concentrations. Keratan sulfate, colominic acid, and Suramine were unable to inhibit PE adherence. Taken together, the results confirm that the 4-sulfate amino sugar moiety, as well as the basic disaccharide structure of N-acetylgalactosamine linked to glucuronic acid, may influence the degree of this molecular interaction. However, other sulfation patterns that could influence the interaction could not be overlooked, as in the case of CSD which contains 2-O-sulfation at glucuronic acid. Studies using pentosan polysulfate, an oversulfated molecule with a xylan backbone, as an inhibitor also showed a reduction of PE adherence of most isolates tested. Thus, only the sulfate content and pattern of this molecule could affect the adhesive interactions. In addition, difference in capacity of low molecular weight heparins to inhibit CSA-mediated PE cytoadherence of clinical isolates was also observed, thereby providing evidence on the heterogeneity in cytoadherence characteristics of maternal parasite isolates as well as their therapeutic potentials.

Animals↗
PubMed1985

Metabolism of the amino acid beta-pyrazol-1-ylalanine and its parent base pyrazole.

beta-Pyrazol-1-yl-DL-alanine, an uncommon amino acid from plants of the Cucurbitaceae, was fed to mice. Although pyrazole is known to affect the liver enzymes UDP-glucose dehydrogenase, UDP-glucuronyl transferase and UDP-glucuronic acid pyrophosphatase, and also depresses their liver glycogen concentrations, beta-pyrazol-1-ylalanine had no such effects. beta-Pyrazol-1-ylalanine could not be detected in the liver of the experimental animals but was present in the urine. No other change in urinary amino acid content was observed. Studies with [14C]-beta-pyrazol-1-yl-DL-alanine showed the administered amino acid was excreted over a 4-day period, 93% of the compound supplied was recovered. Similar recoveries were obtained with the L-enantiomer from cucumber seed. The metabolic inertness of beta-pyrazol-1-ylalanine was also apparent in experiments involving subcutaneous injection of this compound. Administration of pyrazole confirmed an earlier report of resultant increased activity of liver UDP-glucose dehydrogenase and UDP-glucuronyl transferase, and of the depression of activity of liver UDP-glucuronic acid pyrophosphatase. A concomitant 40% decrease in liver glycogen content was seen. The urine contained a novel metabolite, identified as a peptide conjugate of a pyrazole derivative. Mass spectrometry and p.m.r. spectroscopy indicate that this derivative is 3,4,4-trimethyl-5-pyrazolone. The amino acid constituents are aspartic acid, threonine, serine, glutamic acid, proline, glycine, alanine, valine and leucine. The urine of mice receiving pyrazole contained less free glycine and alanine than controls. From the results, it is concluded that pyrazole is not a catabolite of dietary beta-pyrazol-1-ylalanine but to the contrary, the amino acid is essentially excreted unchanged. Formation of 3,4,4-trimethyl-5-pyrazolone from pyrazole would imply C-methylation, a process that has not been previously observed in a mammalian detoxication context.

Amino Acids↗
PubMed1984

Specific inhibition of human beta-D-glucuronidase and alpha-L-iduronidase by a trihydroxy pipecolic acid of plant origin.

The glucuronic acid analogue of 1-deoxynojirimycin, 2(S)-carboxy-3(R), 4(R), 5(S)-trihydroxypiperidine, recently isolated from seeds of Baphia racemosa, is a novel specific inhibitor of human liver beta-D-glucuronidase and alpha-L-iduronidase. No other glycosidases are inhibited. The inhibition of beta-D-glucuronidase is competitive, with a Ki of 8 X 10(-5) M and is pH-dependent. This inhibitor may be useful to induce a mucopolysaccharidosis or to investigate the function of microsomal beta-D-glucuronidase.

Binding, Competitive↗
PubMed2001

Hexuronyl C5-epimerases in alginate and glycosaminoglycan biosynthesis.

The sugar residues in most polysaccharides are incorporated as their corresponding monomers during polymerization. Here we summarize the three known exceptions to this rule, involving the biosynthesis of alginate, and the glycosaminoglycans, heparin/heparan sulfate and dermatan sulfate. Alginate is synthesized by brown seaweeds and certain bacteria, while glycosaminoglycans are produced by most animal species. In all cases one of the incorporated sugar monomers are being C5-epimerized at the polymer level, from D-mannuronic acid to L-guluronic acid in alginate, and from D-glucuronic acid to L-iduronic acid in glycosaminoglycans. Alginate epimerization modulates the mechanical properties of seaweed tissues, whereas in bacteria it seems to serve a wide range of purposes. The conformational flexibility of iduronic acid units in glycosaminoglycans promotes apposition to, and thus functional interactions with a variety of proteins at cell surfaces and in the extracellular matrix. In the bacterium Azotobacter vinelandii the alginates are being epimerized at the cell surface or in the extracellular environment by a family of evolutionary strongly related modular type and Ca(2+)-dependent epimerases (AlgE1-7). Each of these enzymes introduces a specific distribution pattern of guluronic acid residues along the polymer chains, explaining the wide structural variability observed in alginates isolated from nature. Glycosaminoglycans are synthesized in the Golgi system, through a series of reactions that include the C5-epimerization reaction along with extensive sulfation of the polymers. The single, Ca(2+)-independent, epimerase in heparin/heparan sulfate biosynthesis and the Ca(2+)-dependent dermatan sulfate epimerase(s) also generate variable epimerization patterns, depending on other polymer-modification reactions. The alginate and heparin epimerases appear unrelated at the amino acid sequence level, and have probably evolved through independent evolutionary pathways; however, hydrophobic cluster analysis indicates limited similarity. Seaweed alginates are widely used in industry, while heparin is well established in the clinic as an anticoagulant.

Alginates↗
PubMed1998

Mechanisms for covalent binding of benoxaprofen glucuronide to human serum albumin. Studies By tandem mass spectrometry.

Tandem MS has been used to establish the structure and specific binding sites of covalent protein adducts formed upon incubation of the acyl glucuronide of the propionic acid nonsteroidal anti-inflammatory drug benoxaprofen with human serum albumin in vitro. Benoxaprofen 1-O-beta-glucuronide was enzymatically synthesized in vitro and incubated with human serum albumin both in the presence and in the absence of NaCNBH3. The modified human serum albumins were digested with trypsin and separated by HPLC. The modified peptides were detected using HPLC-electrospray MS (with selected-ion monitoring) and were structurally characterized by tandem MS using matrix-assisted laser desorption ionization in both the post-source decay and high-energy collision-induced dissociation modes. These studies established that benoxaprofen glucuronide forms covalent adducts with protein nucleophiles both by nucleophilic displacement of glucuronic acid at the anomeric center and by condensation of the rearranged acyl glucuronic acid isomers with epsilon-amino functions of lysine residues after acyl migration of the aglycone from the anomeric center. Lys-159 was identified as the major binding site. Thus, we have established that members of the less reactive propionic acid class of acyl glucuronides, such as the glucuronide of benoxaprofen, are also capable of reacting with protein nucleophiles to form covalent adducts analogous to those of tolmetin glucuronide (tolmetin is an acetic acid nonsteroidal anti-inflammatory drug), via the mechanisms previously reported from this laboratory, and that the specific covalent binding site profile appears to be drug dependent.

Amino Acid Sequence↗
PubMed1960

The immunological specificity of type II Pneumococcus and its separation into partial specificities. II.

Quantitative data are given on the cross reactions in Type II antipneumococcal horse sera of plant gums and hemicelluloses containing multiple terminal groupings of glucuronic acid and/or 4-O-methylglucuronic acid. Great variability is shown both in the reactivities of the polysaccharides and in the antibodies in the sera of different animals immunized with the same antigen. The 4-O-methyl substituent on the glucuronic acid residues in a gum often appears to diminish cross-precipitation with antibodies to S II.

Animals↗
PubMed1995

A rapid and simple method for the analysis of 1-hydroxypyrene glucuronide: a potential biomarker for polycyclic aromatic hydrocarbon exposure.

The present study describes a simple method of analyzing metabolites of pyrene in urine. This method is capable of detecting the glucuronic acid and sulfate conjugates of pyrene as well as free 1-hydroxypyrene in a single analysis. In comparison to other analytical methods for detecting pyrene metabolites, this new method does not require an overnight enzymatic hydrolysis step and is much more rapid method of analysis. The newly developed procedure involves solid phase extraction of pyrene metabolites followed by separation using HPLC with a phenyl modified reverse phase column and an acidic buffer and acetonitrile gradient elution system. Metabolites were detected using a fluorescence detector with wavelength conditions optimized for each metabolite. This method resulted in baseline separation of the glucuronic acid (1-OH P-GlcUA) and sulfate conjugate (1-OH P-Sul) of 1-hydroxypyrene and free 1-hydroxypyrene (1-OH P). The potential of this method for use in monitoring human exposure to mixtures of PAHs was evaluated by analyzing urine obtained from five individuals working in a coal gasification plant. 1-OH P-GlcUA was detected as the major metabolite in the urine of all the five workers. This metabolite accounted for 80-100% of the total pyrene metabolites excreted in urine. 1-OH P-GlcUA levels ranged from 0.31-0.94 microgram/g creatinine. Low levels of the sulfate conjugate (0.002-0.06 microgram/g creatinine) were detected in four of the samples while free 1-hydroxypyrene (0.07-0.2 microgram/g creatinine) was detected in two of the five urine samples. Urine from occupationally exposed workers was also analyzed for 1-hydroxypyrene following enzymatic hydrolysis using the standard approach. Levels of 1-hydroxypyrene ranged from 0.51-1.17 micrograms/g creatinine. Comparison of the fluorescence intensities of 1-OH P-GlcUA and 1-OH P-Sul to 1-hydroxypyrene demonstrated that the glucuronide conjugate is 3-fold more fluorescent and the sulfate conjugate is 4-fold more fluorescent than 1-hydroxypyrene. These results indicate that conjugates of pyrene, specifically, 1-OH P-GlcUA can potentially be used as a more sensitive biomarker of exposure to PAHs.

Animals↗
PubMed2003

Glucuronidation of etoposide in human liver microsomes is specifically catalyzed by UDP-glucuronosyltransferase 1A1.

A metabolite formed by incubation of human liver microsomes, etoposide, and UDP-glucuronic acid was identified as etoposide glucuronide by liquid chromatography-tandem mass spectrometry analysis. According to the derivatization with trimethylsilylimidazole (Tri-Sil-Z), it was confirmed that the glucuronic acid is linked to an alcoholic hydroxyl group of etoposide and not to a phenolic group. Among nine recombinant human UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A8, UGT1A9. UGT1A10, UGT2B7, and UGT2B15), only UGT1A1 exhibited the catalytic activity of etoposide glucuronidation. The enzyme kinetics in pooled human liver microsomes and recombinant UGT1A1 microsomes showed a typical Michaelis-Menten plot. The kinetic parameters of etoposide glucuronidation were K(m) = 439.6 +/- 70.7 microM and V(max) = 255.6 +/- 19.2 pmol/min/mg of protein in human liver microsomes and K(m) = 503.2 +/- 110.2 microM and V(max) = was 266.5 +/- 28.6 pmol/min/mg of protein in recombinant UGT1A1. The etoposide glucuronidation in pooled human liver microsomes was inhibited by bilirubin (IC(50) = 31.7 microM) and estradiol (IC(50) = 34 microM) as typical substrates for UGT1A1. The inhibitory effects of 4-nitrophenol (IC(50) = 121.0 microM) as a typical substrate for UGT1A6 and UGT1A9, imipramine (IC(50) = 393.8 microM) as a typical substrate for UGT1A3 and UGT1A4, and morphine (IC(50) = 109.3 microM) as a typical substrate for UGT2B7 were relatively weak. The interindividual difference in etoposide glucuronidation in 13 human liver microsomes was 78.5-fold (1.4-109.9 pmol/min/mg of protein). The etoposide glucuronidation in 10 to 13 human liver microsomes was significantly correlated with beta-estradiol-3-glucuronidation (r = 0.841, p < 0.01), bilirubin glucuronidation (r = 0.935, p < 0.01), and the immunoquantified UGT1A1 protein content (r = 0.800, p < 0.01). These results demonstrate that etoposide glucuronidation in human liver microsomes is specifically catalyzed by UGT1A1.

Animals↗
PubMed1993

Influence of growth status on composition of extra-cellular polysaccharides from two Chlamydomonas species.

The extracellular polysaccharides released by Chlamydomonas augustae at the beginning of growth contain mainly arabinose, glucose and galactose. Methylation analysis revealed that the major fraction of these extracellular polysaccharides can be described as a highly branched polymer composed of (1, 3, 4)-linked glucose and terminal arabinose and galactose units. The chemical composition of these extracellular polysaccharides varies during growth and in the stationary phase of growth glucose and glucuronic acid are the main components. The major fraction of the extracellular polysaccharides can be then described as a linear polymer composed of (1, 4)-linked glucose and (1, 4)-linked glucuronic acid. In sharp contrast, the extracellular polysaccharides from C. corrosa are independent of growth status and contain arabinose and galactose as major sugars. Methylation analysis indicated a highly branched polysaccharide composed of arabinose as unique branch point units and of terminal galactose residues.

Amino Acids↗
PubMed1983

Metabolism of benzo(a)pyrene and 1-naphthol in cultured human tumorous and nontumorous colon.

The oxidative metabolism of benzo(a)pyrene and the conjugative metabolism of 1-naphthol by explant cultures of normal human colon and colonic tumor tissue, obtained at surgery, have been studied. After 24 hr in culture, the explants were exposed to either [1-14C]-1-naphthol (20 to 100 microM) or [3H]-benzo(a) pyrene (1.5 microM) for a further 1.5 to 24 hr. Both normal-appearing tissue and tumor tissue metabolized benzo(a)pyrene to a wide variety of organic solvent-soluble metabolites, including monohydroxybenzo(a)pyrenes, dihydrodiols, and tetrols. 1-Naphthol was metabolized by cultured human colonic mucosa and tumor tissue to both its glucuronic acid and sulfate ester conjugates. In the normal tissues, with naphthol (20 microM), sulfate ester conjugation predominated. However, with the tumor tissue, sulfate ester conjugation decreased; thus, the percentage of glucuronic acid conjugates, expressed as a percentage of total metabolites formed, was increased significantly compared to normal tissue. The relationship, if any, of these changes to neoplastic transformation is unclear. The technique of explant culture described in this study may be of use for the study of other facets of the pathobiology of solid tumors.

Adenocarcinoma↗
PubMed1995

Biotransformation of CI-937 in primary cultures of rat hepatocytes. Formation of glutathione conjugates.

The anticancer drug 7,10-dihydroxy-2-[2-[(2-hydroxyethyl)amino]- ethyl]-5-[[2-(methylamino)ethyl]amino]anthra[1,9-c,d]pyrazole- 6(2H)-one dihydrochloride (CI-937) is 1 of 3 anthrapyrazole derivatives chosen for phase I and phase II clinical trials. Although the chemical structure of CI-937 signals a contribution of redox reactions in the pharmacology of the drug, a study concerning the biotransformation of CI-937 is still missing. Incubations of primary cultures of rat hepatocytes with CI-937 result in the formation of three glutathione conjugates and a glucuronic acid conjugate. The structures of the glutathione conjugates have been established by reference synthesis with activated horseradish peroxidase and HPLC-MS-MS and two-dimensional NMR measurements. The glucuronic acid derivative of CI-937 has been identified by MS. The formation of the glutathione conjugates in cells establishes the ability of the drug to form covalent bonding to intracellular nucleophilic targets. The conjugation with glutathione has been rationalized by oxidative activation of CI-937, yielding an electrophilic intermediate that finally reacts with glutathione.

Animals↗
PubMed1985

Mechanisms of chain initiation in the biosynthesis of connective tissue polysaccharides.

Carbohydrate-protein linkages of three types are found in the connective tissue proteoglycans; these linkages involve the following monosaccharide-amino acid pairs: xylose-serine; N-acetylglucosamine-asparagine; and N-acetylgalactosamine-threonine (or serine). The biosynthesis of carbohydrate groups containing linkages of the latter two types presumably occurs by the same pathways that have been well established for many glycoproteins, but details of these processes as they pertain to proteoglycans are not yet known. Initiation of polysaccharide chains linked by the xylose-serine linkage takes place by direct transfer of xylose from UDP-xylose to the hydroxyl groups of specific serine residues in the core proteins of the respective proteoglycans, and the xylosyltransferase catalyzing these reactions has been detected in the rough endoplasmic reticulum of embryonic chick chondrocytes. Although the completed or nascent core proteins are the natural substrates for xylose transfer in the intracellular assembly of proteoglycans, a survey of potential exogenous substrates has shown that small peptides containing alternating serine and glycine residues may also serve as acceptors in this reaction. Nevertheless, larger substrates are preferred, such as chondroitin sulfate proteoglycan, which has been deglycosylated by Smith degradation or HF treatment, or silk fibroin, which contains Ser-Gly pairs. In contrast to the sulfated polysaccharides, which are synthesized by carbohydrate transfer to protein in the endoplasmic reticulum and the Golgi apparatus, hyaluronic acid is formed in the plasma membrane by a different mechanism. The reaction by which chains are initiated is not yet known, but recent work by Prehm suggests that this process occurs either by transfer of the glucuronosyl component of UDP-glucuronic acid to UDP-N-acetylglucosamine or by the converse reaction, i.e., transfer of the N-acetylglucosaminyl unit of UDP-N-acetylglucosamine to UDP-glucuronic acid.

Acetylgalactosamine↗