Ascorbic Acid 2-glucoside Research Articles

Effects of Ascorbic Acid on Gingival Melanin Pigmentation In Vitro and In Vivo

Gingival melanin pigmentation may cause esthetic concerns, even if no serious medical problem is present. As an inhibitor of melanin formation, ascorbic acid is often used to treat skin melanin pigmentation. Thus, the present study investigated the effects of ascorbic acid on gingival melanin pigmentation in vitro and in vivo. The effects of ascorbic acid on melanin formation were evaluated in vitro in B16 mouse melanoma cells and three-dimensional human skin models. In addition, a clinical trial was performed to investigate the inhibitory effects of a gel containing ascorbic acid 2-glucoside (AS-G gel) on gingival melanin pigmentation. This study used a double-masked, split-mouth design on 73 subjects with symmetric gingival melanin pigmentation. AS-G gel was applied to one side of the gingiva for 12 weeks, whereas placebo gel was applied to the other side as a control. Luminance (L*)-value, which describes the lightness of gingiva, was determined by spectrophotometry to obtain an objective measure of melanin pigmentation every 4 weeks. Ascorbic acid significantly inhibited tyrosinase activity and melanin formation in B16 mouse melanoma cells (P <0.01 and P <0.05, respectively). The inhibitory effects of ascorbic acid on melanin formation were also significant in three-dimensional human skin models (P <0.01). Moreover, in the clinical trial, a significant relative change in pigmentation was seen after 4 weeks with the application of AS-G gel compared to placebo (L*-value ratio). Ascorbic acid (AS-G) has potential for the treatment of gingival melanin pigmentation.

Promotion of IL-4- and IL-5-dependent differentiation of anti-μ-primed B cells by ascorbic acid 2-glucoside

The stable ascorbic acid derivative 2- O-α- d-glucopyranosyl- l-ascorbic acid (AA-2G) was used to investigate the role of ascorbic acid (AA) in B cell differentiation in vitro. AA-2G is stable in a solution unlike AA but is hydrolyzed by cellular α-glucosidase to release AA. Mouse spleen B cells were primed for 2 days with an anti-μ antibody in the presence of interleukin (IL)-4 and IL-5 and then washed and recultured with AA-2G in the presence of IL-4 and IL-5. AA-2G, but not AA, dose-dependently increased IgM production, the greatest enhancement being 150% at concentrations of more than 0.5 mM. In the absence of IL-4 and IL-5, primed B cells produced a negligible amount of IgM, and AA-2G had no effect. AA-2G-induced IgM production in the presence of IL-4 and IL-5 was inhibited by the α-glucosidase inhibitor castanospermine. Intracellular AA content, depleted during the priming period, increased by adding AA-2G at the start of reculture. Treatment of B cells with AA-2G resulted in an increase in the number of IgM-secreting cells, CD138-positive cells and CD45R/B220-negative cells. The number of viable cells in untreated cultures decreased gradually, but the decrease was significantly attenuated by AA-2G, resulting in about 70% more viable cells in AA-2G-treated cultures. AA-2G caused a slight but reproducible enhancement of DNA synthesis and a slight decrease in the number of cells with a sub-G1 DNA content. These results demonstrated that AA released from AA-2G enhanced cytokine-dependent IgM production in anti-μ-primed B cells and suggest that its effect is caused through promoting the differentiation of B cells to plasma cells and attenuating the gradual decrease in the number of viable cells.

Radiation Protection by 6-Palmitoyl Ascorbic Acid-2-Glucoside: Studies on DNA Damage in vitro, ex vivo, in vivo and Oxidative Stress in vivo

A palmitoyl derivative of ascorbic acid 2-glucoside, 6-palmitoyl ascorbic acid-2-glucoside (PAsAG), which possess good antioxidant properties, is examined for radioprotection in vitro, ex vivo and in vivo models. PAsAG protected plasmid DNA from gamma-radiation induced damages under in vitro conditions. Presence of 1.6 mM PAsAG inhibited the disappearance of ccc (covalently closed circular) form of plasmid pBR322 with a dose modifying factor of 1.5. Comet assay studies on mouse spleen cells exposed to 6 Gy gamma-radiation (ex vivo) in presence and absence of PAsAG revealed that cellular DNA was effectively protected by this compound from radiation induced damages. Oral administration of 80 mg/kg body weight of PAsAG to mice 1 hour prior to 6 Gy whole body gamma-radiation exposure, efficiently protected cellular DNA in tissues such as spleen, bone marrow and blood, from radiation induced damages as indicated by alkaline comet assay. Oxidative stress in tissues such as liver and brain of mice, following whole body exposure to various doses of gamma-radiation (2-8 Gy), monitored as levels of GSH and peroxidation of lipids, were found considerably reduced when PAsAG was orally administered (80 mg/kg body weight) to the mice one hour prior to the radiation exposure. PAsAG administration improved the per cent survival of mice following exposure to 10 Gy whole body gamma-radiation. Thus PAsAG could act as a radioprotector under in vitro, ex vivo and in vivo conditions of ionizing-radiation exposure.

Synthesis and characterization of PEO–PCL–PEO triblock copolymers: Effects of the PCL chain length on the physical property of W 1/O/W 2 multiple emulsions

A series of poly(ethylene glycol)- block-poly( ɛ-caprolactone)- block-poly(ethylene glycol) (PEO–PCL–PEO) triblock copolymers were prepared and then used for the investigation of the effects of the ratio of ɛ-caprolactone to poly(ethylene glycol) (i.e., [CL]/[EO]) on the physical properties of water-in-oil-in-water (W 1/O/W 2) multiple emulsions containing a model reagent, ascorbic acid-2-glucoside (AA2G). In the synthesis, the [CL]/[EO] was varied from 0.11 to 0.31. The molecular weights and compositions of PEO–PCL–PEO were determined by GPC and 1H NMR analyses. Thermal behavior and crystal formation were studied by DSC, XRD, FT-IR, and polarized optical microscopy (POM). Aggregate behavior of PEO–PCL–PEO was confirmed by DLS, UV, and 1H NMR. Morphology and relative stiffness of the W 1/O/W 2 multiple emulsions in the presence of PEO–PCL–PEO were studied by confocal laser scanning microscopy (CLSM) and rheometer. Variation in the [CL]/[EO] significantly affects the crystalline temperature and spherulite morphology of PEO–PCL–PEO. As the [CL]/[EO] increases, the CMCs of PEO–PCL–PEO decreases and the slope of aggregate size reduction against the copolymer concentration becomes steeper except for the lowest [CL]/[EO] value of PEO–PCL–PEO (i.e., P-222). P-222 significantly increases the viscosity of continuous (W 2) phase, which implies the copolymer would exist in the W 2 phase. On the other hand, the triblock copolymers with relatively high [CL]/[EO] ratios mainly contribute to the size reduction of multiple emulsions and the formation of a firm wall structure. The particle size of the multiple emulsion decreases and the elastic modulus increased as [CL]/[EO] increases, confirmed by microscopic and rheometric analyses.

Essential Role of Ascorbic Acid in Neural Differentiation and Development: High Levels of Ascorbic Acid 2-Glucoside Effectively Enhance Nerve Growth Factor-Induced Neurite Formation and Elongation in PC12 Cells

The aim of this study was to investigate the role of ascorbic acid (AsA) in neural differentiation induced by nerve growth factor (NGF) in PC12 cells, a neural precursor cell line. Cells were cultivated in the presence of L-ascorbic acid-2-O-α-D-glucopyranoside (AA-2G) and evaluated for potentiation of neural differentiation induced by a small amount of NGF. AA-2G enhanced the proportion of neurite-bearing cells in a concentration-dependent manner (< 1m M). When c ultivated with relatively high concentrations of AA-2G (1–5 mM), the cells tended to extend neurites further and to form a neuron-like network. The resultant number of neurite-bearing cells was apparently increased by the addition of AA-2G, with a concurrent decrease in the number of total cells in the same culture dish. These results suggest that AsA in the brain not only promotes NGF-induced differentiation of neural precursor cells but also participates in the development of neural network-forming cells.

Inhibition of free radical-induced erythrocyte hemolysis by 2- O-substituted ascorbic acid derivatives

Inhibitory effects of 2- O-substituted ascorbic acid derivatives, ascorbic acid 2-glucoside (AA-2G), ascorbic acid 2-phosphate (AA-2P), and ascorbic acid 2-sulfate (AA-2S), on 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced oxidative hemolysis of sheep erythrocytes were studied and were compared with those of ascorbic acid (AA) and other antioxidants. The order of the inhibition efficiency was AA-2S≥Trolox=uric acid≥AA-2P≥AA-2G=AA>glutathione. Although the reactivity of the AA derivatives against AAPH-derived peroxyl radical (ROO ) was much lower than that of AA, the derivatives exerted equal or more potent protective effects on AAPH-induced hemolysis and membrane protein oxidation. In addition, the AA derivatives were found to react per se with ROO , not via AA as an intermediate. These findings suggest that secondary reactions between the AA derivative radical and ROO play a part in hemolysis inhibition. Delayed addition of the AA derivatives after AAPH-induced oxidation of erythrocytes had already proceeded showed weaker inhibition of hemolysis compared to that of AA. These results suggest that the AA derivatives per se act as biologically effective antioxidants under moderate oxidative stress and that AA-2G and AA-2P may be able to act under severe oxidative stress after enzymatic conversion to AA in vivo.

Transglucosylation of ascorbic acid to ascorbic acid 2-glucoside by a recombinant sucrose phosphorylase from Bifidobacterium longum

A novel transglycosylation reaction from sucrose to L-ascorbic acid by a recombinant sucrose phosphorylase from Bifidobacterium longum was used to produce a stable L-ascorbic acid derivative. The major product was detected by HPLC, and confirmed to be 2-O-alpha-D-glucopyranosyl-L-ascorbic acid by LC-MS/MS analysis.

Application of ascorbic acid 2-glucoside as a solubilizing agent for clarithromycin: Solubilization and nanoparticle formation

Clarithromycin (CAM) was co-ground with l-ascorbic acid 2-glucoside (AA-2G), a newly developed food additive, to improve the solubility characteristics. The complete solubilizing effect of AA-2G was observed for the ground mixture with 1:1 molar ratio. When ground mixtures of CAM and AA-2G (2:1) were dispersed into water, not only the solubilization of CAM was observed but also nanoparticle formation with a mean particle diameter of 280 nm. The CAM particles obtained in this manner were stable in suspension for at least 7 days. Zeta potential analysis showed that positive charges on the particle surface may be contributing to the stability of the suspension. 1H NMR spectrum of CAM dissolved in a phosphate buffer (pH 5.5) showed a signal derived from the N, N-dimethylamino group at 2.73 ppm, while that of an equimolar ground mixture of CAM with AA-2G in D 2O (pH 5.5) showed clearly two signals at 2.65 and 2.77 ppm derived from the splitting of the two methyl groups. The 13C NMR spectrum of the equimolar ground mixture dissolved in D 2O exhibited two signals derived from N, N-dimethyl carbons of desosamine group at 37.2 and 42.3 ppm, whereas unprocessed CAM showed no resonance signal arising from those carbons. Moreover, the carbon resonance at 163 and 173 ppm arising from the ketone group in the CAM lactone ring shifted downfield to 177 and 180 ppm after the co-grinding with AA-2G. The formation of nanoparticles was only observed when CAM was co-ground with AA-2G in the molar ratio of 2:1, which might be attributable to a grinding-induced interaction in the solid-state via the ketone group in lactone ring of CAM.

Flow Injection Analysis of Ascorbyl Glucoside in Cosmetics by a Disposable Printed‐Circuit Board Waste Modified Electrode

AbstractAscorbyl glucoside, i.e., ascorbic acid 2‐glucoside (AA‐2G), is anew type of stable vitamin C derived compound used in many cosmetic skin‐lightening formulations, but rarely studied in the literature. In this study, a screen printed electrode modified with copper‐enriched printed circuit‐board waste (designated as CuPCB/SPE) was applied to study the electrochemical characteristics of AA‐2G. Cyclic voltammogram of the CuPCB/SPE showed an electrocatalytic oxidative feature at ˜0.6 V vs. Ag/AgCl in 0.15 M NaOH solution. Flow injection analysis coupled with the CuPCB/SPE was further developed for sensitive AA‐2G determination. The calibration plot was linear in the window of 2.5–160 ppm with slope and regression coefficient of 0.0169 μA/ppm and 0.9971, respectively. The detection limit (S/N = 3) was 0.247 ppm. Real sample analysis was demonstrated for different skin‐lightening cosmetic products with appreciable results.

Characterization of the Radical-Scavenging Reaction of 2-O-Substituted Ascorbic Acid Derivatives, AA-2G, AA-2P, and AA-2S: A Kinetic and Stoichiometric Study

The aim of this study was to characterize the antioxidant activity of three ascorbic acid (AA) derivatives O-substituted at the C-2 position of AA: ascorbic acid 2-glucoside (AA-2G), ascorbic acid 2-phosphate (AA-2P), and ascorbic acid 2-sulfate (AA-2S). The radical-scavenging activities of these AA derivatives and some common low molecular-weight antioxidants such as uric acid or glutathione against 1,1-diphenyl-picrylhydrazyl (DPPH) radical, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS+), or galvinoxyl radical were kinetically and stoichiometrically evaluated under pH-controlled conditions. Those AA derivatives slowly and continuously reacted with DPPH radical and ABTS+, but not with galvinoxyl radical. They effectively reacted with DPPH radical under acidic conditions and with ABTS+ under neutral conditions. In contrast, AA immediately quenched all species of radicals tested at all pH values investigated. The reactivity of Trolox, a water-soluble vitamin E analogue, was comparable to that of AA in terms of kinetics and stoichiometrics. Uric acid and glutathione exhibited long-lasting radical-scavenging activity against these radicals under certain pH conditions. The radical-scavenging profiles of AA derivatives were closer to those of uric acid and glutathione rather than to that of AA. The number of radicals scavenged by one molecule of AA derivatives, uric acid, or glutathione was equal to or greater than that by AA or Trolox under the appropriate conditions. These data suggest the potential usage of AA derivatives as radical scavengers.

Suppressive effects of ascorbate derivatives on ultraviolet-B-induced injury in HaCaT human keratinocytes.

The aging of skin, including sunburning, is caused by ultraviolet (UV) irradiation. Here, we examined the inhibitory effect of ascorbic acid (AsA) and its derivatives AsA 2-phosphate (AA-2P) and AsA 2-glucoside (AA-2G) on UV-B- induced cytotoxicity in HaCaT keratinocytes. Results show that cell viability significantly decreased when exposed to UV-B at 0.1-0.4 J/cm2 in a dose-dependent manner. In this study, AsA could not inhibit cytotoxicity, but AA-2P and AA-2G was able to cancel the harmful effect of UV-B when treated at high levels of 0.5-5 mM. These results indicate that the masking of the C-2 OH group may be an effective modification for AsA to inhibit UV-B-induced cytotoxicity in human keratinocytes.

Annexin V assay-proven anti-apoptotic effect of ascorbic acid 2-glucoside after cold ischemia/reperfusion injury in rat liver transplantation.

Controversy exists over whether the predominant cell death of hepatocytes is due to apoptosis or necrosis after ischemia/reperfusion injury. In this study we investigated the predominant cell death of hepatocytes after cold ischemia/reperfusion injury using the Annexin V-based assay, and evaluated the anti-apoptotic effect of ascorbic acid 2-glucoside (AA-2G) added to the University of Wisconsin solution (UW solution) in rat liver transplantation. The retrieved liver was preserved in 4 UW solution for 24 h, and then transplanted orthotopically to the syngeneic Wistar recipient. The animals were divided into 2 groups, a control group (n=10), in which liver grafts were preserved in UW solution (4), and an AA-2G group (n=10), in which liver grafts were preserved in UW solution (4) with AA-2G (100 ug/ml). The serum AST level 4 h after reperfusion in the control group was significantly suppressed in the AA-2G group, and the bile production of the liver graft in the AA-2G group was well recovered. The mean survival time in the AA-2G group was significantly improved compared with that in the control group. Annexin-V and Propidium iodide staining 4 h after reperfusion showed a significantly higher percentage of viable hepatocytes in the AA-2G group compared with the control group (93.4 +/- 2.0 vs. 80.3 +- 2.1%, P<0.05). In the control group, the main cell death of hepatocytes was apoptosis (early apoptosis: 10.0 +- 4.7%, late apoptosis: 6.4 +/- 1.7%). The addition of AA-2G to the UW solution significantly inhibited both early and late apoptotic cell death 4 h after reperfusion (early apoptosis: 0.98 +/- 0.88%, late apoptosis: 2.2 +/- 1.1%). The expression of caspase 9 in the immunostaining of the liver graft was suppressed in the AA-2G group compared with in the control group. Our study using the Annexin V-based assay provided evidence that the predominant cell death of hepatocytes was apoptosis after 24 h cold ischemia/reperfusion injury in rat liver transplantation. The addition of AA-2G to the UW solution attenuated 24 h cold ischemia/reperfusion injury by inhibiting the apoptosis of hepatocytes.

Maintenance of cold-preserved porcine hepatocyte function with UW solution and ascorbic acid-2 glucoside.

Normal human hepatocytes are an ideal source of liver-targeted cell therapies, such as hepatocyte transplantation and bioartificial livers, but availability of human donor livers for liver cell isolation is severely limited. To effectively utilize scarce donor organs for cell therapies, it is of extreme importance to establish an efficient isolation technique and an effective cold preservation solution for transportation of isolated cells. A lateral segment of the liver was surgically resected from pigs weighing 10 kg and a four-step collagenase and dispase digestion was conducted. Isolated hepatocytes were subjected to 8-h cold storage on ice. The following preservation solutions were tested: 1) University of Wisconsin (UW) solution, 2) UW with 100 microg/ml of ascorbic acid-2 glucoside (AA2G), 3) 100% fetal bovine serum (FBS), and 4) Dulbecco's modified Eagle's medium (DMEM) supplemented with 100% FBS. The mean viability of porcine hepatocytes was 95.5 +/- 2.5% when isolated in three independent experiments. Viability, plating efficiency, membrane stability, and ammonia metabolic capacity of cold-preserved hepatocytes were significantly better maintained by the use of UW solution. When AA2G (100 microg/ml) was combined with UW solution, such parameters were further improved. It was explained by inhibition of caspase-3 activation and retention of ATP at high levels of hepatocytes preserved with UW solution containing AA2G. The present work demonstrates that a combination of UW solution with AA2G (100 microg/ml) would be a useful cold preservation means for the development of cell therapies.

Radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl of ascorbic acid 2-glucoside (AA-2G) and 6-acyl-AA-2G.

The radical scavenging activity of the stable derivatives, which are O-substituted at the C-2 position of ascorbic acid (AA), against 1,1-diphenyl-2-picrylhydrazyl (DPPH) was evaluated in buffer under different pH conditions, and compared with those of AA and alpha-tocopherol. AA was shown to have 50% radical scavenging ability (EC50) at a concentration of 2.2 x 10(-5) M against 0.1 mM DPPH in 60% ethanol. Ascorbyl 6-palmitate, a lipophilic AA derivative which has a free endiol group and is therefore unstable, also showed potent radical scavenging activity with EC50 of 2.9 x 10(-5) M. A typical lipophilic antioxidant, alpha-tocopherol gave a similar EC50 value as that of AA. In contrast, ascorbyl 2,6-dipalmitate, AA 2-phosphate and AA 2-sulfate exhibited negligible scavenging activity. On the other hand, 2-O-alpha-D-glucopyranosyl-L-ascorbic acid (AA-2G) and a series of 6-O-acyl-2-O-alpha-D-glucopyranosyl-L-ascorbic acids (6-Acyl-AA-2G) themselves exhibited the radical scavenging activity of EC50: 6.1 x 10(-5) M and 4.4 x 10(-5)-5.9 x 10(-5) M, respectively, although their activities were lower than that of AA. Among 6-Acyl-AA-2G derivatives, the EC50 values tended to decrease with increasing length of their acyl carbon group. Increasing pH of the buffer resulted in decrease in the scavenging activity of all compounds tested as expected. We speculate that the difference in the radical scavenging activity of derivatives O-substituted at the C-2 position of AA may be ascribed to the linkage type of the substituent group to the endiol-lactone resonance system and the degree of dissociation of the C-3 proton.

Anti-transforming nature of ascorbic acid and its derivatives examined by two-stage cell transformation using BALB/c 3T3 cells

The anti-transforming effects of sodium ascorbate and its stable derivatives were examined in the two-stage transformation assay. When BALB/c 3T3 cells were treated with 0.2 μg/ml 20-methylcholanthrene as an initiator, and 100 ng/ml 12- O-tetradecanoylphorbol-13-acetate as a promoter, the addition at the promotion stage of l-ascorbic acid-2-phosphate ester magnesium (APM) was most marked in the inhibition of transformation. The inhibitory effects of sodium ascorbate and ascorbic acid-2-glucoside (AG) were comparable, but weaker than those of APM; l (+)-ascorbic acid-2-sulfate ester disodium 2H 2O showed little effect. When phorbol 12, 13-didecanoate or tumor necrosis factor α (TNF-α) were used as promoters, APM also effectively suppressed transformation.

Ascorbic acid 2-glucoside prevents sinusoidal endothelial cell apoptosis in supercooled preserved grafts in rat liver transplantation

Ascorbic acid 2-glucoside prevents sinusoidal endothelial cell apoptosis in supercooled preserved grafts in rat liver transplantation

Requirement of Cytokines for Augmentation of the Antigen-Specific Antibody Responses by Ascorbate in Cultured Murine T-Cell-Depleted Splenocytes

To gain a better understanding of the possible mechanisms by which a stable form of ascorbate, ascorbic acid 2-glucoside (AA-2G), as an ascorbate source, augments antibody responses, we examined whether AA-2G enhances the anti-sheep-red-blood-cell (SRBC) plaque-forming cell (PFC) responses elicited with distinct interleukins that provide signals for B-cell proliferation and differentiation in cultured murine T-cell-depleted splenocytes. The anti-SRBC PFC responses were markedly reduced by T-cell depletion; and additions of the concanavalin A-stimulated murine splenocytes supernatant (CAS) or interleukin (IL)-1β, IL-2, IL-5, IL-4 or IL-6 to the culture limitedly restored the immune responses. AA-2G synergistically stimulated the anti-SRBC PFC responses in the presence of IL-1β-, IL-2, IL-5 or CAS, IL-1β among these cytokines being most highly affected. However, it failed to enhance the PFC responses elicited by IL-4 or IL-6. Repeated additions of ascorbic acid (AsA) during experimental periods could also produced the enhancing effect, but a single addition of the vitamin did not, because of its instability in the medium. It was shown that exposure to IL-1β, IL-2 or IL-5 must be done at early times after antigen stimulation of the cells to support their optimal responses and that AsA exerted its effect on day 2 and day 3 after the start of culture. These results suggest that AsA may up-regulate the in vitro IgM antibody responses in a cytokine-dependent manner.

Enhancement by ascorbic acid 2-glucoside or repeated additions of ascorbate of mitogen-induced IgM and IgG productions by human peripheral blood lymphocytes.

In this study, the effect of ascorbic acid 2-glucoside (AA-2G), a stable derivative of ascorbic acid (AsA), or repeated additions of ascorbate on antibody productions by human peripheral blood lymphocytes (PBLs) was examined, and the physiological function of AsA was evaluated. When human PBLs were stimulated with Staphylococcus aureus Cowan I or pokeweed mitogen, AA-2G remarkably increased the numbers of IgM- and IgG-secreting cells which were detected by enzyme-linked immunospot assay. Although a single addition of ascorbate was without effect, the effect of AA-2G was remarkably inhibited by the addition of castanospermine, an alpha-glucosidase inhibitor; and moreover, repeated additions of AsA to the culture medium during the culture period enhanced the response to the same level as did a single addition of AA-2G. These results indicate that AsA has the ability to stimulate the immunoglobulin productions by AA-2G. The phytohemagglutinin-induced proliferative response of PBLs was also stimulated by AA-2G. The intracellular AsA content in PBLs cultured with AA-2G was maintained at relatively high levels during the culture period, whereas the content with a single dose of AsA reached nearly zero by the end of the experiment. These in vitro findings suggest that AA-2G and AsA function as potent immunostimulators of antibody production in humans and that the intracellular AsA content is a key parameter for establishing the immune response of PBLs.

Formation of a Stable Ascorbic Acid 2-Glucoside by Specific Transglucosylation with Rice Seedα-Glucosidase

The enzymatic transglucosylation to synthesize a chemically stable form of l-ascorbic acid (AA) was further investigated by using commercially available enzymes. Among various glycosidases examined, only rice seed α-glucosidase could produce a nonreducing and stable glucoside of AA, which was identified as 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2G). The enzyme showed the same regioselective transglucosylase activity as rat intestinal α-glucosidase that had been demonstrated by us to be effective in this reaction, although these two enzymes had different pH optima for maltose hydrolysis. The substrate specificity of rice α-glucosidase for AA-2G formation was considerably different from that of rat α-glucosidase. However, both α-glucosidases had high specificity for the α-1,4-glucosidic linkage but not α-1,6, suggesting that they can catalyze a preferential transglucosylation to the 2-position but not to the 6-position of AA. Thus, these results allows us to produce a sufficient amount of AA-2G with ric...

Formation of a stable ascorbic acid 2-glucoside by specific transglucosylation with rice seed .ALPHA.-glucosidase.

The enzymatic transglucosylation to synthesize a chemically stable form of l-ascorbic acid (AA) was further investigated by using commercially available enzymes. Among various glycosidases examined, only rice seed α-glucosidase could produce a nonreducing and stable glucoside of AA, which was identified as 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2G). The enzyme showed the same regioselective transglucosylase activity as rat intestinal α-glucosidase that had been demonstrated by us to be effective in this reaction, although these two enzymes had different pH optima for maltose hydrolysis. The substrate specificity of rice α-glucosidase for AA-2G formation was considerably different from that of rat α-glucosidase. However, both α-glucosidases had high specificity for the α-1,4-glucosidic linkage but not α-1,6, suggesting that they can catalyze a preferential transglucosylation to the 2-position but not to the 6-position of AA. Thus, these results allows us to produce a sufficient amount of AA-2G with ric...