Effects of δ-aminolaevulinic acid,porphobilinogen and structurally related amino acids on 2-deoxyglucose uptake in cultured neurons

The effects of -aminolaevulinic acid (ALA), porphobilinogen (PBG), -aminobutyric acid (GABA), muscimol, glutamic acid and kainic acid on [³H]2-deoxy-d-glucose uptake by cultured neurons were investigated. Exposure of the cultures for 4 days, to ALA at concentrations as low as 10 M caused a significant, dose-dependent decrease in [³H]2-deoxy-d-glucose uptake. Neither ALA nor PBG appeared to interfere directly with glucose transport into the neuron but 1 mM ALA caused an initial stimulation of [³H]2-deoxy-d-glucose uptake which increased to a maximum after 4 hr and fell to below control values after 19 hr exposure. GABA and muscimol caused similar increases in [³H]2-deoxy-d-glucose uptake but these values remained above control levels after 19 hr exposure. Glutamic acid and kainic acid caused an immediate increase in [³H]2-deoxy-d-glucose uptake which declined to mininum values after 4 hr exposure. The effect of ALA on glucose utilization in neurons may be of particular relevance to patients with acute porphyria where a genetic lesion in neural haem and haemoprotein biosynthesis is postulated to occur. ALA appeared to be more toxic to the neurons than any of the other compounds tested, possibly causing a critical depletion of energy reserves and cell death.     

Enzymic synthesis of the trisaccharide core region of the carbohydrate chain ofN-glycoprotein

Transmannosylation from mannotriose (Man1-4Man1-4Man) to the 4-position at the nonreducing end N-acetylglucosaminyl residue ofN,N-diacetylchitobiose was regioselectively induced through the use of -d-mannanase fromAspergillus niger. The enzyme formed the trisaccharide Man1-4GlcNAc1-4GlcNAc (3.7% of the enzyme-catalysed net decrease ofN,N-diacetylchitobiose) from mannotriose as a donor andN,N-diacetylchitobiose as an acceptor. Mannobiose (Man1-4Man) was also shown to be useful as a donor substrate for the desired trisaccharide synthesis.Abbreviations Man d-mannose - (M _n) (n=1–5) -linkedn-mer of mannose - GlcNAc₂ 2-acetamido-2-deoxy--d-glucopyranosyl-(1–4)-2-acetamido-2-deoxy-d-glucose     

D-Gluconate is an alternative growth substrate for cultivation of Schizosaccharomyces pombe mutants

Schizosaccharomyces pombe cells grow on d-gluconate as the sole carbon and energy source. d-Gluconate is taken up in symport with protons by a specific symporter, pH being the sole driving force. d-Gluconate uptake is independent of the sugar transporting system (e.g. for d-glucose) and of . The carrier is expressed constitutively, and its activity is not subject to glucose repression. Hence, d-gluconate is a suitable carbon and energy source for growth, when d-glucose or other hexoses have to be eliminated e.g. for selection of mutants deficient in hexose transport.Abbreviations 2-DG 2-deoxy-d-glucose - CCCP carbonylcyanide m-chlorophenylhydrazone - pH pH-gradient - electrical potential difference across the plasma membrane - SD standard deviation - SEM standard error of the mean - TPP⁺ tetraphenylphosphonium     

Presence of a sodium-dependentd-glucose transport system in the kidney of the atlantic hagfish (Myxine glutinosa)

Summary A membrane fraction, rich in brushborder membranes, was prepared from the archinephric duct of the atlantic hagfish (Myxine glutinosa) and the uptake ofd-glucose and other sugars into the membrane vesicles was investigated by a rapid filtration technique. Uptake ofd-glucose was found to be sodium-dependent, phloridzin-inhibitable and osmotically sensitive. A sodium gradient dependent overshoot was demonstrated at 25° C as well as at the more physiological temperature of 4°C. The sodium dependentd-glucose transport was inhibited by -methyl-d-glucoside, but not by 2-deoxy-d-glucose. Furthermore at the same concentration of sugars the initial uptake ofd-glucose was 7.2-fold higher thanl-glucose uptake.d-glucose transport across the membrane in the presence of a sodium gradient was stimulated when SCN^– replaced Cl^– and inhibited when gluconate replaced Cl^–.d-glucose uptake in the presence of a sodium- and potassium gradient was decreased by the addition of valinomycin. In addition, the presence of ad-glucose gradient enhanced sodium uptake into the vesicles as compared to a mannitolgradient. Phloridzin inhibited thed-glucose dependent sodium flux. Thus an electrogenic stereospecific sodium glucose co-transport system, with properties similar to that found in the kidney of higher vertebrates is present in this primitive vertebrate and might participate in secondary-active sugar reabsorption in the archinephric duct.     

Transepithelial transport in cell culture:d-Glucose transport by a pig kidney cell line (LLC-PK1)

Summary The pig kidney cell line LLC-PK₁ cultured on a collagen coated membrane filter formed a continuous sheet of oriented asymmetrical epithelial cells joined by occluding junctions. A transepithelial electrical potential (PD) and short-circuit current (SCC) were dependent on the presence of Na and sugar in the apical bathing solution. In the presence of 5.5mm d-glucose, a PD of 2.8 mV, apical surface negative, a SCC of 13 A cm^–2 and transepithelial resistance of 211 ohm·cm² were recorded. The SCC was promptly reduced by the addition of phlorizin to the apical bath but unaffected when placed in the basolateral bath. The effect on SCC of various sugars was compared by the concentrations required for half-maximal SCC: 0.13mm -methyl-d-glucoside, 0.28mm d-glucose, 0.65mm -methyl-d-glucoside, 0.77mm 6-deoxy-d-glucose, 4.8mm d-galactose, and 29mm 3-O-methyl-glucose. When [Na] was reduced, the concentration ofd-glucose required for half-maximal SCC increased. Isotopically labeled³H and¹⁴Cd-glucose were used to simultaneously determine bidirectional fluxes; a resultant net apical-to-basolateral transport was present and abolished by phlorizin. The transported isotope cochromatographed with labeledd-glucose, indicating negligible metabolism of transported glucose. The pig kidney cell line, LLC-PK₁, provides a cell culture model for the investigation of mechanisms of transepithelial glucose transport.     

Monosaccharide transport systems in the yeast Rhodotorula glutinis

By using d-glucose, d-xylose, d-galactose and d-fructose in the strictly aerobic yeast Rhodotorula glutinis and by comparing the half-saturation constants with inhibition constants the yeast was shown to possess a single common system for d-xylose and d-galactose (K _m's and K _i's all between 0.5 and 1.1 mM) but another distinct transport system for d-fructose. The transport of d-glucose has a special position in that glucose blocks apparently allotopically all the other systems observed although it uses at least one of them for its own transport. The different character of d-glucose uptake is underlined by its relative independence of pH (its K _m is completely pH-insensitive) in contrast with all other sugars. At low concentrations, all sugars show mutual positive cooperativity in uptake, suggesting at least two transport sites plus possibly a modifier site on the carrier.     

Anomeric preferences ofd-glucose uptake and utilization by cerebral cortex slices of rats

On aerobic incubation of rat cerebral cortex slices with anomers ofd-glucose and with 2-deoxy-d-glucose (2DG) for 5 min, the disappearance of -d-glucose from the incubation mixture was greater than that of -d-glucose and both anomers had a greater rate of disappearance than that of 2DG. In addition, there were significantly greater consumption of oxygen and production of lactate with the -anomer than with the -anomer. In similar experiments with³H-labeledd-glucose anomers and [1-³H]-3-O-methyl-d-glucose (3MG), the accumulation of [1-³H]--d-glucose (up to 5 min) by rat cerebral cortex slices was greater than that of [1-³H]--d-glucose. Although initially lower than that of the anomers, the accumulation of [1-³H]-3MG increased at a greater rate and, by 5 min of incubation, was greater than that of both glucose anomers. This preferential accumulation was seen to disappear when the slices were preincubated with 2DG (hexokinase inhibitor) or when the temperature of incubation was reduced to 20°C. Under those conditions the data with the glucose anomers were similar to those obtained with 3MG. Our data then suggested that the greater accumulation of -d-glucose than of -d-glucose by the slices was probably not due to differences in transport through brain cell membranes but rather to the preferential metabolism of the -d-glucose.     

Stoichiometric studies of the renal outer cortical brush border membraned-glucose transporter

Summary The stoichiometric properties of the renal outer cortical brush-border membraned-glucose transporter are studied. Experiments which establish the glucose/sodium, glucose/phlorizin and phlorizin/sodium stoichiometries are reported. Three independent methods of determining the substrate/activator (glucose/sodium) stoichiometry for coupled transport systems are presented and discussed. One of these, the Static Head Method, is introduced here for the first time. This type of experiment appears to be more generally applicable than the usual procedure of directly measuring the coupled fluxes of substrate and activator to determine stoichiometric coupling ratios. The results presented in this paper demonstrate that the glucose/sodium/phlorizin stoichiometry of the renal outer cortical brush-border membraned-glucose transport system is 111.     

Purine glucosylating activity in cell suspension cultures ofSolanum tuberosum L.

Cell suspension cultures ofSolanum tuberosum L. cv. Adretta were established from leaf-derived calluses. In the search for purine glucosylating activity, the metabolism of 6-benzylaminopurine was studied. The main metabolite of BA was isolated and identified as 6-benzylaminopurine 7--d-glucopyranoside indicating the occurrence of purine glucosylating activity.Abbreviations BA 6-Benzylaminopurine - [3G]BA BA 3--d-glucopyranoside - [7G]BA BA 7--d-glucopyranoside - [9G]BA BA 9--d-glucopyranoside - RA Radioactivity - R _T Retention Time     

Variant forms ofα-2-l-fucosyltransferase in human submaxillary glands from blood group ABH “secretor” and “non-secretor” individuals

The properties of the -2-l-fucosyltransferases in submaxillary gland preparations from blood group ABH secrefors and non-secretors were compared. The level of activity in the non-secretor gland homogenates amounted to about 5% only of that found in the secretor gland preparations. The enzymes from the two sources differed in solubility properties, charge and affinities for donor and acceptor substrates. The enzyme from secretor glands showed a preference for acceptors with Type 1 [d-galactosyl(1–3)-N-acetyl-d-glucosamine] structures whereas the enzyme from non-secretor glands had a preference for Type 2 [d-galactosyl(1–4)-N-acetyl-d-glucosamine] structures.These results demonstrate that expression of the secretor gene (Se) is associated with a molecular form of the -2-l-fucosyltransferase that is different from the species present in the same tissue when theSe gene is not expressed.     

Biosynthesis of legume-seed galactomannans in vitro

Particulate enzyme preparations were isolated from developing fenugreek (Trigonella foenum-graecum L.) and guar (Cyamopsis tetragonoloba [L.] Taub.) seed endosperms during the period of galactomannan deposition in vivo. These preparations catalysed the formation of polysacharide products from guanosine 5-diphosphate (GDP)-mannose, from uridine 5-diphosphate (UDP)-galactose and from mixtures of the two nucleotides. The products were analysed by solubility, by complete acid hydrolysis, and by selective enzymatic cleavage using pure enzymes of known specificity. With GDP-[U-¹⁴C]-d-mannose as substrate and a divalent metal cation (Mg⁺², Mn⁺², or Ca⁺²) a highly efficient transfer of labelled d-mannosyl residues was obtained to give a product identified as linear (14)--linked d-mannan. No transfer of galactosyl residues was obtained when GDP-[U-¹⁴C]-d-galactose was the only substrate, although very low and variable amounts of an unidentified product which released labelled glucose on acid hydrolysis were formed. In the presence of UDP-galactose, GDP-mannose and Mn⁺² ions, products were formed which have been characterised as galactomanans — a linear (14)--d-mannan backbone carrying d-galactopyranosyl substituents linked (16)- to mannose. The degree of galactose substitution of the d-mannan backbone was manipulated in vitro by varying GDP-mannose concentrations at constant (saturating) UDP-galactose levels. The transfer of d-galactosyl residues from UDP-galactose to galactomannan was absolutely dependent upon the simultaneous transfer of D-mannosyl residues from GDP-mannose. d-Mannan sequences pre-formed in situ using the mannosyltransferase in the absence of UDP-galactose could not become galactose-substituted in a subsequent incubation either with UDP-galactose alone or with UDP-galactose plus GDP-mannose A model for the interaction of GDP-mannose mannosyltransferase and UDP-galactose galactosyltransferase in galactomannan biosynthesis is proposed.Abbreviations GDP guanosine 5-diphosphate - TLC thinlayer chromatography - UDP uridine 5-diphosphate     

l-Ascorbic-acid biosynthesis in the euryhaline diatom Cyclotella cryptica

l-Ascorbic acid (AA) production in cells of Cyclotella cryptica Reimann, Lewin, Guillard (Bacillariophyceae) is enhanced when darkadapted cells are exposed to light.Heterotrophically grown cells incubated with d-[6-³H,6-¹⁴C]glucose and d-[1-³H,6-¹⁴C]glucose (2 h in dark followed by 15 h light) produced labeled AA with significantly different ratios of ³H and ¹⁴C. Comparisons of labeling patterns in AA and chitin-derived d-glucosamine support a path of conversion in Cyclotella from d-glucose to AA that inverts the carbon chain of the sugar. This process resembles similar conversions found in AA-synthesizing animals and species from two other algal classes.Abbreviations AA l-Ascorbic acid - glc d-glucose - glcN d-glucosamine     

Negative-ion fast atom bombardment tandem mass spectrometry for characterization of sulfated unsaturated disaccharides from heparin and heparan sulfate

Negative-ion fast atom bombardment tandem mass spectrometry has been used in the characterization of non-, mono-, di- and trisulfated disaccharides from heparin and heparan sulfate. The positional isomers of the sulfate group of monosulfated disaccharides were distinguished from each other by negative-ion fast atom bombardment tandem mass spectra, which provide an easy way of identifying the positional isomers. This fast atom bombardment collision induced dissociation mass spectrometry/mass spectrometry technique was also applied successfully to the characterization of di- and trisulfated disaccharides.Abbreviations FABMS fast atom bombardment mass spectrometry - CID collision induced dissociation - MIKE mass analysed ion kinetic energy - MS/MS mass spectrometry/mass spectrometry - HPLC high performance liquid chromatography - UA d-gluco-4-enepyranosyluronic acid - CS chondroitin sulfate - DS dermatan sulfate - HA hyaluronan - Hep heparin - HS heparan sulfate - UA(14) GlcNAc 2-acetamido-2-deoxy-4-O-(-d-gluco-4-enepyranosyluronic acid)-d-glucose - UA(14)GlcNAc6S 2-acetamido-2-deoxy-4-O-(-d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-glucose - UA2S(14)GlcNAc 2-acetamido-2-deoxy-4-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-d-glucose - UA2S(14)GlcNAc6S 2-acetamido-2-deoxy-4-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-glucose - UA(14)GlcN6S 2-amino-2-deoxy-4-O-(-d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-glucose - UA2S(14)GlcN 2-amino-2-deoxy-4-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-d-glucose - UA2S(14)GlcN6S 2-amino-2-deoxy-4-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-glucose - UA(14)GlcNS 2-deoxy-2-sulfamino-4-O-(-d-gluco-4-enepyranosyluronic acid)-d-glucose - UA(14)GlcNS6S 2-deoxy-2-sulfamino-4-O-(-d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-glucose - UA2S(14)GlcNS 2-deoxy-2-sulfamino-4-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-d-glucose - UA2S(14)GlcNS6S 2-deoxy-2-sulfamino-4-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-glucose - UA(13)GalNAc 2-acetamido-2-deoxy-3-O-(-d-Gluco-4-enepyranosyluronic acid)-d-galatose - UA(13)GalNAc4S 2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-4-O-sulfo-d-galactose - UA(13)GalNAc6S 2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-galactose - UA2S(13)GalNAc 2-acetamido-2-deoxy-3-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-d-galactose - UA2S(13)GalNAc4S 2-acetamido-2-deoxy-3-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-4-O-sulfo-d-galactose - UA2S(13)GalNAc6S 2-acetamido-2-deoxy-3-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-galactose - UA(13)GalNAcDiS 2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-4,6-di-O-sulfo-d-galactose - UA(13)GlcNAc 2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-d-glucose.     

Callus proliferation from the protoplasts of embryogenic cells of Quercus serrata

Embryogenic culture was induced from the immature embryos of Quercus serrata using Marashige and Skoog's medium (MS) containing 0.1 M each of 2,4-d and BAP, and subcultured for seven months before isolation of protoplasts by using 1% Cellulase RS in 0.6 M mannitol solution. Efficient colony formation was obtained when protoplasts were cultured in a liquid MS medium containing 0.6 M mannitol, 3% sucrose and combination of 0.1 M or 1 M each of 2,4-d and BAP. Excluding ammonium nitrate from the MS medium resulted in the decrease of the percentage of colony formation. From colonies, both agar culture and liquid culture were sustained in the MS media without mannitol containing no plant growth regulator, or containing 0.1 M of BAP in combination with 0.1 M or 1 M of 2,4-d.Abbreviations BAP 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - MS medium after Murashige & Skoog (1962).     

Enzymic synthesis of lacto-N-triose II and its positional analogues

N-acetylhexosaminidase fromNocardia orientalis catalysed the synthesis of lacto-N-triose II glycoside (-d-GlcNAc-(1-3)--d-Gal-(1-4)--d-Glc-OMe,3) with its isomers -d-GlcNAc-(1-6)--d-Gal-(1-4)--d-Glc-OMe (4) and -d-Gal-(1-4)-[-d-GlcNAc-(1-6)]--d-Glc-OMe (5) throughN-acetylglucosaminyl transfer fromN,N-diacetylchitobiose (GlcNAc₂) to methyl -lactoside. The enzyme formed the mixture of trisac-charides3, 4 and5 in 17% overall yield based on GlcNAc₂, in a ratio of 20:21:59. Withp-nitrophenyl -lactoside as an acceptor, the enzyme also producedp-nitrophenyl -lacto-N-trioside II (-d-GlcNAc-(1-3)--d-Gal-(1-4)--d-Glc-OC₆H₄NO₂-p,6) with its isomers -d-GlcNAc-(1-6)--d-Gal-(1-4)--d-Glc-OC₆H₄NO₂-p (7) and -d-Gal-(1-4)-[-d-GlcNAc-(1-6)]--d-Glc-OC₆H₄NO₂-p (8). In this case, when an inclusion complex ofp-nitrophenyl lactoside acceptor with -cyclodextrin was used, the regioselectivity of glycosidase-catalysed formation of trisaccharide glycoside was substantially changed. It resulted not only in a significant increase of the overall yield of transfer products, but also in the proportion of the desired compound6.Abbreviations GlcNAc₂ 2-acetamido-2-deoxy--d-glucopyranosyl-(1-4)-2-acetamido-2-deoxy-d-glucose - NAHase N-acetylhexosaminidase - -CD -cyclodextrin     

Glucose uptake into plasma membrane vesicles from the maternal surface of human placenta

Summary Glucose uptake into plasma membrane vesicles from the maternal surface of the human placenta was measured with the Millipore filtration technique. Uptake ofd-glucose was dependent on the osmolarity of the incubation medium surrounding the vesicles. Uptake ofd-glucose exceeded that ofl-glucose. The uptake ofd-glucose was not enhanced by placing 100mm NaCl or NaSCN in the medium outside the vesicles (none inside) at the onset of uptake determinations.d-glucose transport was inhibited by cytochalasin B; phloretin, phlorizin, and 1-fluoro-2,4-dinitrobenzene.d-glucose uptake was inhibited by 2-deoxy-d-glucose, 3-O-methyl-d-glucose and to a lesser extent byd-galactose. It was not inhibited by -methyl-d-glucoside. Cytochalasin B binding to the vesicles was 30% inhibited in the presence of 80mm d-glucose. The results indicate that the system for facilitated transport ofd-glucose at the maternal face of the placenta is distinctly different from that on the brush-border membrane of intestine or renal tubule and more closely resembles that of human erythrocyte.     

Glycosylation with thioglycosides activated by dimethyl(methylthio)sulfonium tetrafluoroborate: synthesis of two trisaccharide glycosides corresponding to the blood group A and B determinants

Two trisaccharide glycosides,p-trifluoroacetamidophenylethyl 3-O-(2-acetamido-2-deoxy--d-galactopyranosyl)-2-O-(-l-fucopyranosyl)--d-galactopyranoside andp-trifluoroa-cetamidophenylethyl 2-O-(-l-fucopyranosyl)-3-O-(-d-galactopyranosyl)--d-galactopyranoside, corresponding to the human blood group A and B determinants, were synthesized. A key fucosylgalactosyl disaccharide derivative was glycosylated with galactosaminyl or galactosyl donors, respectively. Dimethyl (thiomethyl)sulfonium tetrafluoroborate was used for thioglycoside activation in coupling reactions.     

Semipermeable membranes for improving the histochemical demonstration of enzyme activities in tissue sections

Summary Improved histochemical multi-step techniques for the demonstration of glucose 6-phosphate isomerase and phosphoglucomutase in tissue sections are described. With these techniques a semipermeable membrane is interposed between the incubating solutions and the tissue sections preventing diffusion of enzymes into the medium during incubation. In the histochemical system the glucosephosphate isomerase converts the substrate d-fructo-furanose 6-phosphoric acid to d-gluco-pyranose 6-phosphoric acid, and the phosphoglucomutase converts the substrate -d-glucose 1-phosphate to the same reagent, which in turn is oxidized, by exogenous and endogenous glucose 6-phosphate dehydrogenase to d-glucono--lactone 6-phosphoric acid. Concomittantly the electrons are transferred via NADP⁺, phenazine methosulphate and menadione to nitro-BT. Sodiumazide and amytal are incorporated to block electron transfer to the cytochromes.     

Function and presumed molecular structure of Na+-D-glucose cotransport systems

Functional characterization of Na⁺-d-glucose cotransport in intestine and kidney indicates the existence of heterogeneous Na⁺-d-glucose cotransport systems. Target size analysis of the transporting unit and model analysis of substrate binding have been performed and proteins have been cloned which mediate (SGLT1) and modulate (RS1) the expression of Na⁺-d-glucose cotransport. The experiments support the hypothesis that functional Na⁺-d-glucose cotransport systems in mammals are composed of two SGLT1-type subunits and may contain one or two RS1-type proteins. SGLT1 contains up to twelve membrane-spanning -helices, whereas RS1 is a hydrophilic extracellular protein which is anchored in the brush-border membrane by a hydrophobic -helix at the C-terminus. SGLT1 alone is able to translocate glucose together with sodium; however, RS1 increases the V _max of transport expressed by SGLT1. In addition, the biphasic glucose dependence of transport, which is typical for kidney and has been often observed in intestine, was only obtained after coexpression of SGLT1 and RS1.     

A membrane-bound enzyme complex synthesising glucan and glucomannan in pine tissues

Particulate membrane preparations isolated from cambial cells and differentiating and differentiated xylem cells of pine (Pinus sylvestris L.) trees synthesised [¹⁴C]glucans using either guanosine 5-diphosphate (GDP)-D-[U-¹⁴C]glucose or uridine 5-diphosphate (UDP)-D-[U-¹⁴C]glucose as glycosyl donors. Although these glucans had -(13) and -(14) linkages in an approximate ratio 1:1, the distribution of the linkages in the glucan synthesised from GDP-D-glucose was different from that synthesised from UDP-D-glucose. The synthesis of the mixed -(13) and -(14) glucan from GDP-D-[U-¹⁴C]glucose was changed to that of -(14) glucomannan in the presence of increasing concentrations of GDP-D-mannose. The glucan formed from UDP-D-[U-¹⁴C]glucose was not affected by any concentration of GDP-D-mannose. The membrane preparations epimerized GDP-D-glucose to GDP-D-mannose; however, the low amount of GDP-D-mannose formed was not incorporated into the polymer becaus the affinity of the synthase for GDP-D-glucose was much greater than that for GDP-D-mannose. The glucan formed from GDP-D-glucose and the glucomannan formed from GDP-D-glucose together with GDP-D-mannose were characterized. The apparent K _m and V _max of the glucan synthase for GDP-D-glucose were 6.38 M and 5.08 M·min^-1, respectively. No lipid intermediates were detected during the synthesis of either glucan or glucomannan. The results indicated that an enzyme complex for the formation of the glucomannan was bound to the membrane.Abbreviations GDP guanosine 5-diphosphate - GLC gasliquid chromatography - UDP trridine 5-diphosphate