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Enzymatic preparation of rare sugars as an alternative to traditional sweeteners is an effective strategy to achieve a low-calorie healthy diet. Ribose-5-phosphate isomerase B (RpiB) is a key enzyme in the non-oxidative branch of the catalytic pentose phosphate pathway. Here, we investigated the potential of Curtobacterium flaccumfaciens ZXL1 (C. flaccumfaciens ZXL1) derived RpiB (CfRpiB) in D-allose preparation. The optimal reaction conditions for recombinant CfRpiB were found experimentally to be pH 7.0, 55 °C, and no metal ions. The kinetic parameters Km, kcat, and catalytic efficiency kcat/Km were 320 mM, 4769 s−1, and 14.9 mM−1 s−1 respectively. The conversion of D-allulose by purified enzyme (1 g L−1 ) to D-allose was 13% within 1 h. In addition, homology modeling and molecular docking were used to predict the active site residues: Asp13, Asp14, Cys72, Gly73, Thr74, Gly77, Asn106, and Lys144. [ABSTRACT FROM AUTHOR]

A novel l-rhamnose isomerase was identified and cloned from an extreme-temperature aquatic habitat metagenome. The deduced amino acid sequence homology suggested the possible source of this metagenomic sequence to be Chloroflexus islandicus. The gene expression was performed in a heterologous host, Escherichia coli, and the recombinant protein l-rhamnose isomerase (L-RIM) was extracted and purified. The catalytic function of L-RIM was characterized for d-allulose to d-allose bioconversion. d-Allose is a sweet, rare sugar molecule with anti-tumour, anti-hypertensive, cryoprotective, and antioxidative properties. The characterization experiments showed L-RIM to be a Co++- or Mn++-dependent metalloenzyme. L-RIM was remarkably active (~ 80%) in a broad spectrum of pH (6.0 to 9.0) and temperature (70 to 80 °C) ranges. Optimal L-RIM activity with d-allulose as the substrate occurred at pH 7.0 and 75 °C. The enzyme was found to be excessively heat stable, displaying a half-life of about 12 days and 5 days at 65 °C and 70 °C, respectively. L-RIM catalysis conducted at slightly acidic pH of 6.0 and 70 °C achieved biosynthesis of about 30 g L−1 from 100 g L−1d-allulose in 3 h. Key points: • The present study explored an extreme temperature metagenome to identify a novel gene that encodes a thermostable l-rhamnose isomerase (L-RIM) • L-RIMexhibits substantial (80% or more) activity in a broad spectrum of pH (6.0 to 9.0) and temperature (70 to 80 °C) ranges • L-RIMis excessively heat stable, displaying a half-life of about 12 days and 5 days at 65 °C and 70 °C, respectively [ABSTRACT FROM AUTHOR]

A putative l-rhamnose isomerase (l-RI) gene from Paenibacillus baekrokdamisoli was expressed as a recombinant enzyme in Escherichia coli BL21(DE3) and characterized as a producer of d-allose from d-allulose. Recombinant l-RI from P. baekrokdamisoli was homogeneously purified on SDS-PAGE with a 46 kDa molecular mass and specific activity of 1.27 U/mg by His-Trap affinity chromatography. The enzyme was estimated to be a tetramer in enzyme active form because its molecular mass was determined to be approximately 190 kDa by Gelfiltration chromatography. In the isomerization reaction between d-allose and d-allulose, recombinant l-RI exhibited the highest activity at pH 8.0 and 60°C in the presence of 0.5 mM Mn2+. The half-lives of the enzyme at 50, 55, 60, 65, 70, and 75°C were 417, 57, 27, 20, 3.3, and 0.2 h, respectively. The Michaelis-Menten constants (Km), turnover numbers (kcat), and catalytic efficiencies (kcat/Km) of the enzyme for d-allose and d-allulose were 33 mM, 13.79 s−1, and 0.4 mM−1s−1 and 45.24 mM, 6.58 s−1, and 0.14 mM−1s−1, respectively. The enzyme showed isomerization activity for aldoses with right-handed configuration of hydroxyl group at the C-2 and C-3 positions, such as l-mannose, l-lyxose, d-gulose, d-allose, and d-ribose. During production of d-allose from d-allulose, the enzyme produced 125 g/L of d-allose from 500 g/L of d-allulose in 3 h with 41.6 g/L/h productivity with 104 U/mL enzyme. We first reported the l-RI from the Paenibacillus genus, and the results suggested that the P. baekrokdamisolil-RI could be applied as a d-allose producer. [ABSTRACT FROM AUTHOR]

Chemical investigation of the stems and leaves of Passiflora edulis Sims led to the isolation of a pair of phenylethanoid glycosides (1, 2), two benzyl alcohol glycosides (3, 4), and two cyanogenic glycosides (5, 6). Compounds 1 and 2 were an inseparable mixture in a 1:2 ratio. The structures were identified by spectroscopic analysis and comparison with literature data. Compound 1 was a new phenylethanoid alloside, and compound 2 was found in this plant for the first time. [ABSTRACT FROM AUTHOR]

d-Allose is a rare sugar, can be used as an ingredient in a range of foods and dietary supplements, has alimentary activities, especially excellent anti-cancer effects and used in assisting cancer chemotherapy and radiotherapy, etc. To develop a simple and low-cost process for d-allose production, a one-pot enzymatic process using the substrate of d-fructose, and the recombinant enzymes of d-psicose 3-epimerase (DPE) and l-rhamnose isomerase (l-RhI) was developed. These enzymes were cloned from Ruminococcus sp. and B. subtilis, respectively, successfully expressed in E. coli, extracted and immobilized using anion exchange resin and amino resin, respectively. The mass ratio of d-fructose, d-psicose and d-allose was 6.6:2.4:1.0 when the reaction reached equilibrium after 5 h of reaction. Using the low-cost substrate of d-fructose, the reusable immobilized enzymes and the one-pot reaction, the production process is simplified and the production cost is decreased. In addition, to simplify the enzyme extraction and immobilization processes, new methods for enzyme capture and immobilization were developed especially for DPE immobilization. This is the first report for one-pot d-allose production using immobilized l-RhI and DPE. [ABSTRACT FROM AUTHOR]

Objective: Two fluorine-18-labeled analogues, 3-deoxy-3-[18F]fluoro-D-allose (3-[18F]FDA) and 6-deoxy-6-[18F]fluoro-D-allose (6-[18F]FDA), were synthesized and their potentials of diagnostic property were characterized.Methods: In vitro rat red blood cell (RBC) transport and phosphorylation by yeast hexokinase were evaluated in comparison with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG). The rate of protein binding in pooled human serum was measured by an ultrafiltration method. In vivo metabolite analysis in mice was also performed. Biodistribution, urine excretion, and in vivo renal kinetics in mice were compared with 2-deoxy-2-[18F]fluorosorbitol ([18F]FDS).Results: Rat RBC uptake of 3- and 6-[18F]FDA (7.8 ± 2.5%ID and 10.2 ± 4.8%ID, respectively) was significantly lower than that of [18F]FDG (44.7 ± 8.7%ID). RBC uptake of 3-[18F]FDA was inhibited by D-glucose (30%) and cytochalasin B (40%), indicating the involvement of GLUT1-dependent transport. In contrast, 6-[18F]FDA transport was not inhibited by D-glucose and cytochalasin B. 3- and 6-[18F]FDA were not phosphorylated by yeast hexokinase under the conditions that result in 60% conversion of [18F]FDG into [18F]FDG-6-phosphate within 30 min. Serum protein binding of 3- and 6-[18F]FDA was negligible. Metabolic transformation of both tracers was not detected in plasma and urine at 30 min after injection. The highest tissue uptake of both tracers was observed in kidneys. Heart and brain uptake of both tracers was below blood levels throughout the biodistribution studies (until 120 min after injection). No significant uptake in the bone was observed, indicating the absence of de-fluorination in mice. In vivo PET imaging visualized rapid excretion of the administered 3- and 6-[18F]FDA from the kidneys, with minimal tracer accumulation in other organs. The urine excretion rate of 3-[18F]FDA was much lower than that of 6-[18F]FDA and [18F]FDS.Conclusions: 3- and 6-[18F]FDA might be unsatisfactory for tumor imaging. In contrast, these tracers demonstrated high levels of kidney uptake and excretion, low serum protein binding, and high metabolic stability as preferable properties for renal imaging. Notably, the urine excretion rate and kidney uptake kinetics of 6-[18F]FDA were comparable with those of the potential renal imaging agent [18F]FDS. Further validation studies in animal models are required to confirm the feasibility of 6-[18F]FDA as a functional renal imaging agent. [ABSTRACT FROM AUTHOR]

l-Rhamnose isomerase (L-RI, EC 5.3.1.14), catalyzing the isomerization between l-rhamnose and l-rhamnulose, plays an important role in microbial l-rhamnose metabolism and thus occurs in a wide range of microorganisms. It attracts more and more attention because of its broad substrate specificity and its great potential in enzymatic production of various rare sugars. In this article, the enzymatic properties of various reported L-RIs were compared in detail, and their applications in the production of l-rhamnulose and various rare sugars including d-allose, d-gulose, l-lyxose, l-mannose, l-talose, and l-galactose were also reviewed. [ABSTRACT FROM AUTHOR]

Now a days sugar free food are very much popular because of their less calorie content. So food industry uses various artificial sweeteners which are low in calorie content instead of high calorie sugar. U.S. Food and Drug Administration has approved aspartame, acesulfame-k, neotame, cyclamate and alitame for use as per acceptable daily intake (ADI) value. But till date, breakdown products of these sweeteners have controversial health and metabolic effects. On the other hand, rare sugars are monosaccharides and have no known health effects because it does not metabolize in our body, but shows same sweet taste and bulk property as sugar. Rare sugars have no such ADI value and are mainly produced by using bioreactor and so inspite of high demand, rare sugars cannot be produced in the desired quantities. [ABSTRACT FROM AUTHOR]

We previously reported that a rare sugar d-allose, which is the d-glucose epimer at C3, inhibits the gibberellin-dependent responses such as elongation of the second leaf sheath and induction of α-amylase in embryo-less half seeds in rice (Fukumoto et al. ). d-Allose suppresses expressions of gibberellin-responsive genes downstream of SLR1 protein in the gibberellin-signaling through hexokinase (HXK)-dependent pathway. In this study, we discovered that d-allose induced expression of ABA-related genes including OsNCED1- 3 and OsABA8ox1- 3 in rice. Interestingly, d-allose also up-regulated expression of OsABF1, encoding a conserved bZIP transcription factor in ABA signaling, in rice. The d-allose-induced expression of OsABF1 was diminished by a hexokinase inhibitor, d-mannoheptulose (MNH). Consistently, d-allose also inhibited Arabidopsis growth, but failed to trigger growth retardation in the glucose- insensitive2 ( gin2) mutant, which is a loss-of-function mutant of the glucose sensor AtHXK1. d-Allose activated AtABI5 expression in transgenic gin2 over-expressing wild-type AtHXK1 but not in gin2 over-expressing the catalytic mutant AtHXK1, indicating that the d-allose phosphorylation by HXK to d-allose 6-phosphate (A6P) is the first step for the up-regulation of AtABI5 gene expression as well as d-allose-induced growth inhibition. Moreover, overexpression of OsABF1 showed increased sensitivity to d-allose in rice. These findings indicated that the phosphorylation of d-allose at C6 by hexokinase is essential and OsABF1 is involved in the signal transduction for d-allose-induced growth inhibition. [ABSTRACT FROM AUTHOR]

The gene coding for ribose-5-phosphate isomerase (Rpi) from Thermotoga lettingae TMO was cloned and expressed in E. coli. The recombinant enzyme was purified by Ni-affinity chromatography. It converted d-psicose to d-allose maximally at 75 °C and pH 8.0 with a 32 % conversion yield. The k, turnover number ( k), and catalytic efficiency ( k k) for substrate d-psicose were 64 mM, 6.98 min and 0.11 mM min respectively. [ABSTRACT FROM AUTHOR]

One of the rare sugars, d-allose, which is the epimer of d-glucose at C3, has an inhibitory effect on rice growth, but the molecular mechanisms of the growth inhibition by d-allose were unknown. The growth inhibition caused by d-allose was prevented by treatment with hexokinase inhibitors, d-mannoheptulose and N-acetyl- d-glucosamine. Furthermore, the Arabidopsis glucose-insensitive2 ( gin2) mutant, which is a loss-of-function mutant of the glucose sensor AtHXK1, showed a d-allose-insensitive phenotype. d-Allose strongly inhibited the gibberellin-dependent responses such as elongation of the second leaf sheath and induction of α-amylase in embryo-less half rice seeds. The growth of the slender rice1 ( slr1) mutant, which exhibits a constitutive gibberellin-responsive phenotype, was also inhibited by d-allose, and the growth inhibition of the slr1 mutant by d-allose was also prevented by d-mannoheptulose treatment. The expressions of gibberellin-responsive genes were down-regulated by d-allose treatment, and the down-regulations of gibberellin-responsive genes were also prevented by d-mannoheptulose treatment. These findings reveal that d-allose inhibits the gibberellin-signaling through a hexokinase-dependent pathway. [ABSTRACT FROM AUTHOR]

d-Allose has attracted a great deal of attention in recent years due to its many pharmaceutical activities, which include anti-cancer, anti-tumor, anti-inflammatory, anti-oxidative, anti-hypertensive, cryoprotective, and immunosuppressant activities. d-Allose has been produced from d-psicose using d-allose-producing enzymes, including l-rhamnose isomerase, ribose-5-phosphate isomerase, and galactose-6-phosphate isomerase. In this article, the properties, applications, and metabolism of d-allose are described, and the biochemical properties of d-allose-producing enzymes and their d-allose production are reviewed and compared. Moreover, several methods for effective d-allose production are suggested herein. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the protective effects of d-allose, a rare sugar, on pressure-induced ischemia during vitrectomy in the rabbit eye. Methods: The rabbits underwent pars plana vitrectomy, and continuous intraocular irrigation at a perfusion pressure of 140 mmHg was performed for 45 min. Intraocular pressure was regulated by adjusting the height of a bottle of balanced saline solution containing d-allose. Morphometric studies were performed to study the effects of d-allose on the histological changes induced by ischemia in the rabbit retina. Electroretinograms (ERGs) were taken before and 1 and 7 days after vitrectomy. Nitroblue tetrazolium was used as an index of superoxide anion (O) generation. Data were analyzed by use of the unpaired Student's t test. Results: Seven days after ischemia, significant reductions in both number of ganglion cells and the thickness of the inner plexiform layer were observed. d-Allose significantly inhibited ischemic injury of the inner retina ( P < 0.05). On postoperative day 7, amplitudes of ERG b-waves were significantly lower in the control group than in the d-allose group ( P < 0.05). d-Allose suppressed the production of O. Conclusions: Intraocular irrigation with d-allose during vitrectomy may protect the retina against ischemia-induced damage. [ABSTRACT FROM AUTHOR]

Ribose-5-phosphate isomerase from Clostridium thermocellum converted d-psicose to d-allose, which may be useful as a pharmaceutical compound, with no by-product. The 12 active-site residues, which were obtained by molecular modeling on the basis of the solved three-dimensional structure of the enzyme, were substituted individually with Ala. Among the 12 Ala-substituted mutants, only the R132A mutant exhibited an increase in d-psicose isomerization activity. The R132E mutant showed the highest activity when the residue at position 132 was substituted with Ala, Gln, Ile, Lys, Glu, or Asp. The maximal activity of the wild-type and R132E mutant enzymes for d-psicose was observed at pH 7.5 and 80°C. The half-lives of the wild-type enzyme at 60°C, 65°C, 70°C, 75°C, and 80°C were 11, 7.0, 4.2, 1.5, and 0.6 h, respectively, whereas those of the R132E mutant enzymes were 13, 8.2, 5.1, 3.1, and 0.9 h, respectively. The specific activity and catalytic efficiency ( k/ K) of the R132E mutant for d-psicose were 1.4- and 1.5-fold higher than those of the wild-type enzyme, respectively. When the same amount of enzyme was used, the conversion yield of d-psicose to d-allose was 32% for the R132E mutant enzyme and 25% for the wild-type enzyme after 80 min. [ABSTRACT FROM AUTHOR]

Development of effective agents for treatment of hormone-refractory prostate cancer (HRPC) has become a national medical priority. d-Allose is a monosaccharide (C-3 epimer of glucose) distributed rarely in nature; because of its scarcity and cost, the biological effect has hardly been studied. In the present study, we demonstrated the inhibitory action of d-allose on proliferation of human HRPC cell lines, DU145 and PC-3 in a dose- and time-dependent manner, while human normal prostate epithelial (NPE) cell line, PrEC showed no remarkable effect. In vitro treatment of d-allose resulted in the alteration of Bcl-2/Bax ratio in favor of apoptosis (programmed cell death, PCD) in both the HRPC cell lines, which was associated with the lowering of mitochondrial transmembrane potential (Δψm) and the release of cytochrome C (cyt C), the cleavage of caspase 3 and poly (ADP-ribose) polymerase (PARP), and the elevation of calcium concentration in cytosol ([Ca2+]c). d-Allose also induced G1 phase arrest of the cell cycle in DU145 cell line. This study for the first time suggested the antiproliferative effect of d-allose through induction of PCD in HRPC cell lines, which could be due to the modulation of mitochondria mediated intrinsic apoptotic pathway. [ABSTRACT FROM AUTHOR]

The rpiB gene, encoding ribose-5-phosphate isomerase (RpiB) from Clostridium thermocellum, was cloned and expressed in Escherichia coli. RpiB converted d-psicose into d-allose but it did not convert d-xylose, l-rhamnose, d-altrose or d-galactose. The production of d-allose by RpiB was maximal at pH 7.5 and 65°C for 30 min. The half-lives of the enzyme at 50°C and 65°C were 96 h and 4.7 h, respectively. Under stable conditions of pH 7.5 and 50°C, 165 g d-allose l− 1 was produced without by-products from 500 g d-psicose l−1 after 6 h. [ABSTRACT FROM AUTHOR]

d-Allose, a rare sugar, is one of the potent inhibitors of ischemia/reperfusion injury of the rat liver. To investigate the potency of this powerful agent we examined its effect against ischemia/reperfusion injury and compared it to that of allopurinol and superoxide dismutase. Male Lewis rats were given water ad libitum preoperatively for 12 h and anesthetized by isoflurane inhalation anesthesia. Drugs were administered through a polyethylene catheter inserted into the portal vein for 2 h ( d-allose), 10 min (allopurinol), or 5 min (superoxide dismutase) before ischemia, and the livers were then subjected to 70% ischemia, induced by crossclamping the vessels to the lateral and median lobes of the liver for 90 min. Rats were divided into four groups: group 1, pretreated with vehicle (normal saline); group 2, treated with d-allose; group 3, treated with allopurinol; and group 4, treated with superoxide dismutase. The effects of the drugs were evaluated by liver hemodynamics, neutrophil count, myeloperoxidase, liver enzymes, and histological studies. d-Allose improved liver hemodynamics ( P < 0.001) and postischemic animal survival ( P < 0.05) significantly compared with the control group and nonsignificantly compared with the allopurinol and superoxide dismutase groups. Myeloperoxidase activity in the postischemic liver tissue was decreased significantly ( P < 0.05) by d-allose compared with all other treatment and control groups. Neutrophil count was also significantly ( P < 0.05) decreased in the d-allose group compared with than that in the control group, as well as the superoxide dismutase group. Only d-allose produced a statistically significant decrease in the level of liver enzymes, compared with levels in the control group. The moderately protective effect of d-allose, which caused no clinical side effects, is encouraging. d-Allose had the best protective effect against neutrophil-related postischemic injury of the liver tissue, followed by allopurinol and superoxide dismutase. However, a more extensive study is needed to ensure the effects as well as the mechanisms of the effect of this rare sugar. [ABSTRACT FROM AUTHOR]