Transient and long-lasting openings of the mitochondrial permeability transition pore can be monitored directly in intact cells by changes in mitochondrial calcein fluorescence

The structures of glycans N-linked to Arabidopsis proteins have been fully identified. From immuno- and affinodetections on blots, chromatography, nuclear magnetic resonance, and glycosidase sequencing data, we show that Arabidopsis proteins are N-glycosylated by high-mannose-type N-glycans from Man5GlcNAc2 to Man9GlcNAc2, and by xylose- and fucose (Fuc)-containing oligosaccharides. However, complex biantenary structures containing the terminal Lewis a epitope recently reported in the literature (A. -C. Fitchette-Lainé, V. Gomord, M. Cabanes, J.-C. Michalski, M. Saint Macary, B. Foucher, B. Cavalier, C. Hawes, P. Lerouge, and L. Faye [1997] Plant J 12: 1411-1417) were not detected. A similar study was done on the Arabidopsis mur1 mutant, which is affected in the biosynthesis of L-Fuc. In this mutant, one-third of the Fuc residues of the xyloglucan has been reported to be replaced by L-galactose (Gal) (E. Zablackis, W.S. York, M. Pauly, S. Hantus, W.D. Reiter, C.C.S. Chapple, P. Albersheim, and A. Darvill [1996] Science 272: 1808-1810). N-linked glycans from the mutant were identified and their structures were compared with those isolated from the wild-type plants. In about 95% of all N-linked glycans from the mur1 plant, L-Fuc residues were absent and were not replaced by another monosaccharide. However, in the remaining 5%, L-Fuc was found to be replaced by a hexose residue. From nuclear magnetic resonance and mass spectrometry data of the mur1 N-glycans, and by analogy with data reported on mur1 xyloglucan, this subpopulation of N-linked glycans was proposed to be L-Gal-containing N-glycans resulting from the replacement of L-Fuc by L-Gal.     

The MUR1 gene of Arabidopsis thaliana encodes an isoform of GDP-D-mannose-4,6-dehydratase, catalyzing the first step in the de novo synthesis of GDP-L-fucose

GDP-L-fucose is the activated nucleotide sugar form of L-fucose, which is a constituent of many structural polysaccharides and glycoproteins in various organisms. The de novo synthesis of GDP-L-fucose from GDP-D-mannose encompasses three catalytic steps, a 4,6-dehydration, a 3,5-epimerization, and a 4-reduction. The mur1 mutant of Arabidopsis is deficient in L-fucose in the shoot and is rescued by growth in the presence of exogenously supplied L-fucose. Biochemical assays of the de novo pathway for the synthesis of GDP-L-fucose indicated that mur1 was blocked in the first nucleotide sugar interconversion step, a GDP-D-mannose-4,6-dehydratase. An expressed sequence tag was identified that showed significant sequence similarity to proposed bacterial GDP-D-mannose-4,6-dehydratases and was tightly linked to the mur1 locus. A full-length clone was isolated from a cDNA library, and its coding region was expressed in Escherichia coli. The recombinant protein exhibited GDP-D-mannose-4,6-dehydratase activity in vitro and was able to complement mur1 extracts in vitro to complete the pathway for the synthesis of GDP-L-fucose. All seven mur1 alleles investigated showed single point mutations in the coding region for the 4,6-dehydratase, confirming that it represents the MUR1 gene.     

Xyloglucan from xylem-differentiating zones of Cryptomeria japonica

Xyloglucan was isolated from xylem-differentiating zones of Cryptomeria japonica. Endo-1,4-beta-glucanase digestion of the xyloglucan gave a series of oligosaccharides. These oligosaccharides were purified by gel permeation chromatography and normal-phase HPLC. Glycosyl-residue composition and glycosyl-linkage composition analyses. 1H NMR spectroscopy and FAB-mass spectrometry of the oligosaccharides showed that the xyloglucan was composed of five kinds of oligosaccharide. These oligosaccharides are commonly found in xyloglucan from dicot plants and are characterized as XXXG, XXLG, XXFG, XLLG and XLFG. These results suggest that xyloglucan from gymnosperms has similar structure to that of dicots.     

Dimers of a GFG hexasaccharide occur in apple fruit xyloglucan

Apple fruit xyloglucan is predominantly built up from XXXG, XXFG, and XLFG units (G = beta-D-Glcp-, X = alpha-D-Xylp-(1-->6)-beta-D-Glcp-, L = beta-D-Galp-(1-->2)-alpha-D-Xylp-(1-->6)-beta-D-Glcp-, F = alpha-L-Fucp-(1-->2)-beta-D-Galp-(1-->2)-alpha-D-Xyl p-(1-->6)-beta-D-Glcp-). However, small amounts of oligosaccharides with a less heavily branched glucan backbone also occur. Structural analysis of two such oligosaccharides, isolated from a xyloglucan preparation digested with endoglucanase i.v., using a combination of FAB mass spectrometry and 1H NMR spectroscopy, afforded the identification of GFG and a dimer of GFG. The finding of the dodecasaccharide GFGGFG as a structural element of apple fruit xyloglucan is most unusual.     

Pathomorphology of rat lungs during postradiation period

The xyloglucan from cotyledons of Hymenaea courbaril was hydrolysed with endo-(1,4)-beta-D-glucanase (cellulase) and analysed by TLC and HPAEC. The limit digest was different from those obtained from xyloglucans of Tamarindus indica and Copaifera langsdorffii. On treatment with nasturtium beta-galactosidase, two main oligosaccharides were detected by TLC and HPAEC. Using a process of enzymatic sequencing involving alternate treatments with a pure xyloglucan oligosaccharide-specific alpha-xylosidase, and a pure beta-glucosidase, both from nasturtium, their structures were deduced to be XXXG and a new oligosaccharide XXXXG. These structures were confirmed by 1H NMR. The relative proportions of XXXG and XXXXG indicate that approximately half of the subunits in Hymenaea xyloglucan are based on the new oligosaccharides. In the native polymer the XXXXG subunits are likely to carry galactosyl substituents in varying proportions, since cellulase hydrolysates contained many bands which were converted to XXXXG on hydrolysis with nasturtium beta-galactosidase. Although no comparative studies on the physico-chemical properties of Hymenaea courbaril xyloglucan have yet been performed, our results indicate that this polymer is less interactive with iodine when compared with T. indica and C. langsdorffii xyloglucans, suggesting that changes in conformation may occur due to the presence of XXXXG.     

Functions of Xyloglucan in Plant Cells

While an increase in the number of xyloglucan tethers between the cellulose microfibrils in plant cell walls increases the walls' rigidity, the degradation of these tethers causes the walls to loosen. Degradation can occur either through the integration of xyloglucan oligosaccharides due to the action of xyloglucan endotransglucosylase or through direct hydrolysis due to the action of xyloglucanase. This is why the addition of xyloglucan and its fragment oligosac-charides causes plant tissue tension to increase and decrease so dramatically. Experiments involving the overexpression of xyloglucanase and cellulase have revealed the roles of xyloglucans in the walls. The degradation of wall xyloglucan in poplar by the transgenic expression of xyloglucanase, for example, not only accelerated stem elongation in the primary wall, but also blocked upright-stem gravitropism in the secondary wall. Overexpression of cellulase also reduced xyloglucan content in the walls as cellulose microfibrils were trimmed at their amorphous region, resulting in increased cell volume in Arabidopsis leaves and in sengon with disturbed leaf movements. The hemicellulose xyloglucan, in its function as a tether, plays a key role in the loosening and tightening of cellulose microfibrils: it enables the cell to change its shape in growth and differentiation zones and to retain its final shape after cell maturation.     

Weak substrate binding to transport proteins studied by NMR

The weak binding of sugar substrates fails to induce any quantifiable physical changes in the L-fucose-H+ symport protein, FucP, from Escherichia coli, and this protein lacks any strongly binding ligands for competitive binding assays. Access to substrate binding behavior is however possible using NMR methods which rely on substrate immobiliza-tion for detection. Cross-polarization from proton to carbon spins could detect the portion of 13C-labeled substrate associated with 0.2 micromol of the functional transport system overexpressed in the native membranes. The detected substrate was shown to be in the FucP binding site because its signal was diminished by the unlabeled substrates L-fucose and L-galactose but was unaffected by a three- to fivefold molar excess of the non-transportable stereoisomer D-fucose. FucP appeared to bind both anomers of its substrates equally well. An NMR method, designed to measure the rate of substrate exchange, could show that substrate exchanged slowly with the carrier center (>10(-1) s), although its dynamics are not necessarily coupled strongly to this site within the protein. Relaxation measurements support this view that fluctuations in the interaction with substrate would be confined to the binding site in this transport system.     

Structural analysis of xyloglucan oligosaccharides by the post-source decay fragmentation method of MALDI-TOF mass spectrometry: influence of the degree of substitution by branched galactose, xylose, and fucose on the fragment ion intensities

Highly branched xyloglucan oligosaccharides were analyzed by the post-source decay (PSD) fragmentation method of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The ratio of [M-Xyl]+ and [M-Gal]+ fragment ion intensities could be used to characterize the degree of Gal substitution at the non-reducing end, because the number of possible chemical species was directly related to their relative ion intensity. The intensity of the [M-Fuc]+ ion was predominantly strong in the fragment spectrum of fucosyl oligosaccharides as the first fragmentation, indicating the fucosyl linkage to be much weaker than the other glycosidic linkages in the MALDI-PSD fragmentation. Setting fragment ion [M-Fuc]+ to the pseudo precursor ion [MF]+, the second fragmentation ions were produced from [MF]+ in the drift region in PSD fragmentation of fucosyl oligosaccharides.     

The biosynthetic pathway of vitamin C in higher plants

Vitamin C (L-ascorbic acid) has important antioxidant and metabolic functions in both plants and animals, but humans, and a few other animal species, have lost the capacity to synthesize it. Plant-derived ascorbate is thus the major source of vitamin C in the human diet. Although the biosynthetic pathway of L-ascorbic acid in animals is well understood, the plant pathway has remained unknown-one of the few primary plant metabolic pathways for which this is the case. L-ascorbate is abundant in plants (found at concentrations of 1-5 mM in leaves and 25 mM in chloroplasts) and may have roles in photosynthesis and transmembrane electron transport. We found that D-mannose and L-galactose are efficient precursors for ascorbate synthesis and are interconverted by GDP-D-mannose-3,5-epimerase. We have identified an enzyme in pea and Arabidopsis thaliana, L-galactose dehydrogenase, that catalyses oxidation of L-galactose to L-galactono-1,4-lactone. We propose an ascorbate biosynthesis pathway involving GDP-D-mannose, GDP-L-galactose, L-galactose and L-galactono-1,4-lactone, and have synthesized ascorbate from GDP-D-mannose by way of these intermediates in vitro. The definition of this biosynthetic pathway should allow engineering of plants for increased ascorbate production, thus increasing their nutritional value and stress tolerance.     

L-fucose residues on cellulose-based dialysis membranes: quantification of membrane-associated L-fucose and analysis of specific lectin binding

Contact of mononuclear human leukocytes with cellulose dialysis membranes may result in complement-independent cell activation, i.e. enhanced synthesis of cytokines, prostaglandins and an increase in beta 2-micro-globulin synthesis. Cellular contact activation is specifically inhibited by the monosaccharide L-fucose suggesting that dialysis membrane associated L-fucose residues are involved in leukocyte activation. In this study we have detected and quantitated L-fucose on commercially-available cellulose dialysis membranes using two approaches. A sensitive enzymatic fluorescence assay detected L-fucose after acid hydrolysis of flat sheet membranes. Values ranged from 79.3 +/- 3.6 to 90.2 +/- 5.0 pmol cm-2 for Hemophan or Cuprophan respectively. Enzymatic cleavage of terminal alpha-L-fucopyranoses with alpha-L-fucosidase yielded 7.7 +/- 3.3 pmol L-fucose per cm2 for Cuprophan. Enzymatic hydrolysis of the synthetic polymer membranes AN-69 and PC-PE did not yield detectable amounts of L-fucose. In a second approach, binding of the fucose specific lectins of Lotus tetragonolobus and Ulex europaeus (UEAI) demonstrated the presence of biologically accessible L-fucose on the surface of cellulose membranes. Specific binding was observed with Cuprophan, and up to 2.6 +/- 0.3 pmol L-fucose per cm2 was calculated to be present from Langmuir-type adsorption isotherms. The data presented are in line with the hypothesis that surface-associated L-fucose residues on cellulose dialysis membranes participate in leukocyte contact activation.     

Analysis of the oligosaccharide units of xyloglucans by digestion with isoprimeverose-producing oligoxyloglucan hydrolase followed by anion-exchange chromatography

A method for rapidly identifying six of the most commonly found xyloglucan oligosaccharide units, XXXG, XLXG, XXLG, XLLG, XXFG, and XLFG was developed by high-performance anion exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) before and after digestion with purified isoprimeverose-producing oligoxyloglucan hydrolase (IPase). Using this method, the compositions of oligosaccharide units of soybean and mung bean xyloglucans were re-examined. Significant amounts of oligosaccharides that have not previously been reported to be oligosaccharide units of soybean and mung bean xyloglucans were found.     

In vivo evaluation of the miniaturized Gyro centrifugal pump as an implantable ventricular assist device

A method has been developed for the rapid molecular mass determination and structural elucidation of mixtures of oligosaccharides derived from plant cell walls. The oligosaccharides were fractionated using gel permeation chromatography and 'analytical' high-performance anion-exchange chromatography (HPAEC), neutralized, dried and the mixtures of eluent salt and oligosaccharides were per-O-acetylated directly. The derivatized oligosaccharides were isolated by dissolution in dichloromethane and the salts were removed by aqueous partitioning. The per-O-acetylated oligosaccharides were analysed using electrospray (ES) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MS). Exploiting the fact that acid-catalysed per-O-acetylation of oligosaccharides can be achieved even under the extremely salty conditions that are found in post-column neutralized HPAEC fractions, and combining this derivatization step with off-line ESMS, allow rapid screening for molecular mass and thus yield information on the composition of the various oligosaccharides in these complex mixtures. Subsequent per-O-methylation of the per-O-acetylated, salt-free fractions and collision-induced dissociation tandem mass spectrometric analysis was used for additional sequence and branching determination of the oligosaccharides.     

Detection of novel carbohydrate binding activity of interleukin-1

Tamm-Horsfall glycoprotein (THGP) and the oligosaccharide fraction liberated from THGP by hydrazinolysis inhibited tetanus toxoid-induced T cell proliferation. Intact THGP showed approximately 100-fold more inhibitory activity than the free oligosaccharides. After fractionating the oligosaccharides by anion-exchange column chromatography, the inhibitory activity could be detected in a sialidase-resistant acidic oligosaccharide fraction (fraction AR). The inhibitory activity of fraction AR was not observed when the fraction was added to the T cell culture medium 24 h after the addition of tetanus toxoid. Increased concentration of interleukin (IL) 1beta and decreased concentration of IL-2 were observed in the T cell culture medium after the addition of fraction AR. The oligosaccharides in fraction AR also inhibited the growth of an IL-1-dependent cell line, D10-G4. These results strongly suggested that the oligosaccharides in fraction AR bind to IL-1beta and suppress its cytokine activity. IL-1beta actually bound to the fraction AR immobilized on an amino-bonded thin layer plate. Fractionation of the oligosaccharides indicated that only oligosaccharides containing an N-acetylgalactosamine residue and a sulfate residue bound specifically to IL-1beta. Removal of either the sulfate residue or the N-acetylgalactosamine residue from the oligosaccharides abolished both the proliferation-inhibition and IL-1beta binding activities. Since IL-1beta did not bind to thyroid-stimulating hormone, which has the sulfate group at C-4 of the N-acetylgalactosamine residue in its N-linked sugar chains, the binding of IL-1beta toward oligosaccharides in fraction AR was considered to be highly specific.     

Macrophage recognition of saccharide chains on the erythrocytes damaged by iron-catalyzed oxidation

Mouse erythrocytes oxidized with an iron catalyst ADP/Fe3+ chelate attached to the monolayers of mouse resident and thioglycollate-induced peritoneal macrophages in the absence of serum, indicating that the macrophages recognized the oxidized erythrocytes. The recognition was partially prevented when the oxidized cells were treated with dithiothreitol, suggesting that disulfide formation is involved, in part, in the generation of the membrane sites recognized by macrophages. Phosphatidylserine is unlikely to be the determinant on the oxidized cells because it was not detected on the outer surface of the oxidized cells. The recognition by resident macrophages was effectively inhibited by N-acetylneuramin lactose, N-acetylneuraminic acid, glycophorin A, and disialoganglioside GD1a, but poorly by lactose, asialoglycophorin A, and monosialoganglioside GM1. In addition, the recognition was partially inhibited by L-fucose and human lactoferrin. The recognition by thioglycollate-induced macrophages was not inhibited by glycophorin A but was partially inhibited by L-fucose, lactoferrin, and oligosaccharides from band 3 glycoprotein. Enzymatic cleavage of the poly-N-acetyllactosaminyl saccharide chains of band 3 and lactoferrin resulted in a loss of the inhibitory activity. These results suggest that sialosaccharide chains of ADP/Fe(3+)-oxidized erythrocytes, possibly those on glycophorin A, are mainly involved in the recognition by resident macrophages, and poly-N-acetyllactosaminyl saccharide chains, possibly those on band 3, are partly involved in the recognition both by resident and thioglycollate-induced macrophages. Oxidation of erythrocytes may induce change in these membrane glycoproteins, like aggregation, which renders their saccharide chains susceptible to the macrophage recognition.     

Xyloglucan endotransglycosylation in suspension-cultured poplar cells

Xyloglucan endotransglycosylase activity was identified and defined by transfer of a part of xyloglucan to reduced xyloglucan heptasaccharide ([3H]XXXGol) in an enzyme preparations from suspension-cultured poplar cells. Although the activity was distributed in buffer-soluble and buffer-insoluble fractions associated with cells and in the extracellular fraction, it was mostly recovered in the buffer-insoluble fraction, suggesting that the enzyme was bound to the cell wall. The affinity for acceptor XXXGol was increased at a higher concentration of donor xyloglucan with a constant Vmax. The Vmax for donor xyloglucan was increased at a higher concentration of the oligosaccharide without any change in affinity. These kinetic data suggest that the acceptor acts by combining with the enzyme independently of the donor. The velocity of the reaction decreased gradually as the heptasaccharide units was increased from two to four, suggesting that the xyloglucan endotransglycosylase reaction caused donor xyloglucan substantially to decrease in molecular size. The activity in buffer-soluble fraction was increased by ABA in auxin-starved cells, when cultured in MS medium containing various plant hormones. Nevertheless, the activity increased markedly at the exponential growth and decreased immediately at the stationary phase of cells in the presence of 2,4-D. The activity of xyloglucan endotransglycosylase is developmentally regulated during the growth but is not directly induced by plant hormones.     

Structure of the N-linked oligosaccharides that show the complete loss of alpha-1,6-polymannose outer chain from och1, och1 mnn1, and och1 mnn1 alg3 mutants of Saccharomyces cerevisiae

The periplasmic invertase was purified from Saccharomyces cerevisiae och1::LEU2 disruptant cells (delta och1), which have a defect in elongation of the outer chain attached to the N-linked core oligosaccharides (Nakayama, K., Nagasu, T., Shimma, Y., Kuromatsu, J., and Jigami, Y. (1992) EMBO J. 11, 2511-2519). Structural analysis of the pyridylaminated (PA) neutral oligosaccharides released by hydrazinolysis and N-acetylation confirmed that the och1 mutation causes a complete loss of the alpha-1,6-polymannose outer chain, although the PA oligosaccharides (Man9GlcNAc2-PA and Man10GlcNAc2-PA), in which one or two alpha-1,3-linked mannose(s) attached to the endoplasmic reticulumn (ER)-form core oligosaccharide (Man8GlcNAc2) were also detected. Analysis of the delta och1 mnn1 strain oligosaccharides released from total cell mannoprotein revealed that the delta och1 mnn1 mutant eliminates the alpha-1,3-mannose attached to the core and accumulates predominantly a single ER-form oligosaccharide species (Man8GlcNAc2), suggesting a potential use of this strain as a host cell to produce glycoproteins containing mammalian high mannose type oligosaccharides. The delta och1 mnn1 alg3 mutants accumulated Man5GlcNAc2 and Man8GlcNAc2 in total cell mannoprotein, confirming the lack of outer chain addition to the incomplete corelike oligosaccharide and the leaky phenotype of the alg3 mutation. All the results suggest that the OCH1 gene encodes an alpha-1,6-mannosyltransferase that is functional in the initiation of alpha-1,6-polymannose outer chain addition to the N-linked core oligosaccharide (Man5GlcNAc2 and Man8GlcNAc2) in yeast.     

Profiling glycoprotein n-linked oligosaccharide by capillary electrophoresis

A method for analysis of N-linked oligosaccharides derived from glycoproteins including sialic acid-containing species is presented. It is based on the combination of specific chemical and enzymatic conversions coupled with capillary electrophoretic (CE) separation and laser-induced fluorescence (LIF) detection. Glycoproteins were heat-denatured in the presence of a reducing agent and the N-linked oligosaccharides were released by peptide N-glycosidase (PNGase F; EC3.5.1.52)-catalyzed hydrolysis. The released N-linked oligosaccharides were derivatized with 8-aminopyrene-1,3,6-trisulfonate (APTS) under mild reductive amination conditions in which desialylation and loss of fucose residues are minimized. A model N-linked oligosaccharide, desialylated, galactosylated biantennary, core-substituted with fucose (A2F) was tested for APTS-based derivatization chemistry with excellent recovery of the adduct without losing fucose and neuraminic acid residues. The profiles of heavily sialylated N-linked oligosaccharides derived from fetuin, recombinant human erythropoietin and kallikrein are reported and the data show that the present method produces a high resolution of the N-linked oligosaccharide profile for fingerprinting glycans derived from glycoproteins.     

Role of asparagine-linked oligosaccharides in protein folding, membrane targeting, and thyrotropin and autoantibody binding of the human thyrotropin receptor

The amino-terminal ectodomain of thyrotropin (TSH) receptor (TSHR) is heavily glycosylated with asparagine-linked (N-linked) oligosaccharides. The present studies were designed to evaluate how acquisition and processing of N-linked oligosaccharides play a role in the functional maturation of human TSHR. A glycosylation inhibitor tunicamycin, which inhibits the first step of N-linked glycosylation (acquisition of N-linked oligosaccharides), and a series of mutant Chinese hamster ovary (CHO)-Lec cells defective in the different steps of glycosylation processing were used. Inhibition of acquisition of N-linked oligosaccharides by tunicamycin treatment in CHO cells stably expressing TSHR produced nonglycosylated TSHR, which was totally nonfunctional. In contrast, all of the TSHRs synthesized in mutant CHO-Lec1, 2, and 8 cells (mannose-rich, sialic acid-deficient, and galactose-deficient oligosaccharides, respectively) bound TSH and produced cAMP in response to TSH with an affinity and an EC50 similar to those in TSHR expressed in parental CHO cells (CHO-TSHR; sialylated oligosaccharides). However, Lec1-TSHR and Lec2-TSHR were not efficiently expressed on the cell surface, whereas the expression levels of Lec8-TSHR and CHO-TSHR were essentially identical. All of the TSHRs expressed in CHO-Lec cells cleaved into two subunits. Finally, anti-TSHR autoantibodies from Graves' patients interacted with all of the TSHRs harboring different oligosaccharides to a similar extent. These data demonstrate that acquisition and processing of N-linked oligosaccharides of TSHR appear to be essential for correct folding in the endoplasmic reticulum and for cell surface targeting in the Golgi apparatus. We also show that complex type carbohydrates are not crucially involved in the interaction of TSHR with TSH and anti-TSHR autoantibodies.     

Structure and mechanism of L-fucose isomerase from Escherichia coli

The three-dimensional structure of L-fucose isomerase from Escherichia coli has been determined by X-ray crystallography at 2.5 A resolution. This ketol isomerase converts the aldose L-fucose into the corresponding ketose L-fuculose using Mn2+ as a cofactor. Being a hexamer with 64,976 Da per subunit, L-fucose isomerase is the largest structurally known ketol isomerase. The enzyme shows neither sequence nor structural similarity with other ketol isomerases. The hexamer obeys D3 symmetry and forms the crystallographic asymmetric unit. The strict and favorably oriented local symmetry allowed for a computational phase extension from 7.3 A to 2.5 A resolution. The structure was solved with an L-fucitol molecule bound to the catalytic center such that the hydroxyl groups at positions 1 and 2 are ligands of the manganese ion. Most likely, L-fucitol mimics a bound L-fucose molecule in its open chain form. The protein environment suggests strongly that the reaction belongs to the ene-diol type.     

Selective binding of fucose-recognizing lectin on the cone photoreceptor outer segments

The distribution of fucose-containing glycoconjugates in the photoreceptor cell layer of rat and human retinas was examined by lectin histochemistry using Aleuria aurantia lectin (AAL), which recognizes L-fucose alpha 1, 6 residue. In the rate retina, AAL diffusely bound to the apical outer segments and to the basal inner segments, whereas it bound to the entire outer segments of other photoreceptors, which were considered to be cones due to their proportion. In the human retina, AAL bound diffusely to the basal inner segments and to the retinal pigment epithelia, but it bound selectively to the outer segments of the cones. The present findings revealed that the glycoconjugates, whose sugar chains contain L-fucose alpha 1, 6 residue on their termini, are present in the cone outer segments.