Maltose Molecules Research Articles

The Catalytic Influence of Polymers and Surfactants on the Rate Constants of Reaction of Maltose with Cerium (IV) in Acidic Aqueous Medium

Kinetics of the reaction of maltose with cerium ammonium sulfate were analyzed spectrophotometrically by observing the decrease of the absorbance of cerium (IV) at 385 nm in the presence and absence of polyethylene glycols (600, 1500, and 4000) and polyvinylpyrrolidone (PVP), in addition to anionic micelles of sodium dodecyl sulfate (SDS), cationic micelles of cetyltrimethylammonium bromide (CTAB) and non-ionic micelles of Tween 20 surfactants. Generally, there is little literature about using the polymers (PEGs and PVP) as catalysts in the oxidation-reduction reactions. Therefore, the major target of this work was to investigate the influence of the nature of polymers and surfactants on the oxidation rates of maltose by cerium (IV) in acidic aqueous media, as well as employing the Piszkiewicz model to explain the catalytic effect. The kinetic runs were derived by adaptation of the pseudo first-order reaction conditions with respect to the cerium (IV). The reaction was found to be first-order with respect to the oxidant and fractional-order to maltose and H2SO4. The reaction rates were enhanced in the presence of polymer and micellar catalysis. Indeed, the surfactants were found to work perfectly close to their critical micelle concentrations (CMC). Electrostatic interaction and H-bonding appear to play an influential role in binding maltose molecules to polymer/surfactant micelles, while oxidant ions remain at the periphery of the Stern layer within the micelle.

Stoichiometric Conversion of Maltose for Biomanufacturing by In Vitro Synthetic Enzymatic Biosystems.

Maltose is a natural α-(1,4)-linked disaccharide with wide applications in food industries and microbial fermentation. However, maltose has scarcely been used for in vitro biosynthesis, possibly because its phosphorylation by maltose phosphorylase (MP) yields β-glucose 1-phosphate (β-G1P) that cannot be utilized by α-phosphoglucomutase (α-PGM) commonly found in in vitro synthetic enzymatic biosystems previously constructed by our group. Herein, we designed an in vitro synthetic enzymatic reaction module comprised of MP, β-phosphoglucomutase (β-PGM), and polyphosphate glucokinase (PPGK) for the stoichiometric conversion of each maltose molecule to two glucose 6-phosphate (G6P) molecules. Based on this synthetic module, we further constructed two in vitro synthetic biosystems to produce bioelectricity and fructose 1,6-diphosphate (FDP), respectively. The 14-enzyme biobattery achieved a Faraday efficiency of 96.4% and a maximal power density of 0.6 mW/cm2, whereas the 5-enzyme in vitro FDP-producing biosystem yielded 187.0 mM FDP from 50 g/L (139 mM) maltose by adopting a fed-batch substrate feeding strategy. Our study not only suggests new application scenarios for maltose but also provides novel strategies for the high-efficient production of bioelectricity and value-added biochemicals.

Role of Mono- and Disaccharide Combination in Cryoprotective Medium for Rooster Semen to Ensure Cryoresistance of Spermatozoa.

The combination of saccharides in the composition of a cryopreservation medium may represent a promising method for the preservation of the reproductive cells of male birds. In the current study, cryoprotective media with a combined composition of mono- and di-saccharides were developed. The degree of penetration of reducing saccharide molecules (maltose—Mal20 medium) and non-reducing disaccharide molecules (trehalose—Treh20 medium) from the cryoprotective medium into the cytosol of rooster spermatozoa was studied. LCM control media without disaccharides were used as the control. The number of maltose molecules penetrating from the outside into the cytosol of the spermatozoon was 1.06 × 104, and the number of trehalose molecules was 3.98 × 104. Using a combination of maltose and fructose, the progressive motility of frozen/thawed semen and the fertility rates of eggs were significantly higher ((p < 0.05) 40.2% and 68.5%, respectively) than when using a combination of trehalose and fructose in a cryoprotective diluent (33.4% and 62.4%, respectively). A higher rate of chromatin integrity at the level of 92.4% was obtained when using Treh20 versus 74.5% Mal20 (p < 0.05). Maltose positively affected the preservation of frozen/thawed sperm in the genital tract of hens. On the seventh day from the last insemination when using Mal20, the fertilization of eggs was 42.6% and only 27.3% when using Treh20. Despite the same molecular weight, maltose and trehalose have different physicochemical and biological properties that determine their function and effectiveness as components of cryoprotective media.

Type I hypersensitivity elicited by an electrolytic solution containing 5% maltose

Urticaria due to maltose. Electrolytic solutions containing sugar are widely used in clinical settings, and allergic reactions are very rare. We report a case of an allergic reaction elicited by the injection of an electrolytic solution containing 5% maltose. A 44-year-old woman underwent surgery for myoma uteri and a left ovarian chocolate cyst. During anesthesia induction, hives and throat discomfort appeared several minutes after intravenous injection of electrolytic solution containing 5% maltose (Potacol R®, Otsuka), thiamine hydrochloride, and ascorbic acid. Prick tests for these three injection drugs were negative. We therefore performed diagnostic challenges with each of these injection drugs. Thiamine hydrochloride and ascorbic acid produced no reactions. Challenge with Potacol R® (150 mL/h) elicited wheals on her abdomen, arms, and right thigh 60 minutes after the start of the injection (Figure 1A). The cutaneous lesions resolved within 90 minutes. Potacol R® contains 5% maltose, 0.6% sodium chloride, 0.31% sodium lactate, 0.03% potassium chloride, and 0.02% calcium chloride. Prick tests for the individual components were negative, and only an intradermal test for maltose was positive. A total of four healthy subjects showed a negative reaction to maltose intradermal test. Medical gloves were used during the surgery and allergy skin tests, but no allergic reactions appeared except for an intradermal test for maltose. We exclude latex allergy and attribute her urticaria to maltose. Electrolytic solutions containing 5% maltose are widely used infusion fluids. Allergic reactions were rarely reported, and most were type I hypersensitivity.1-3 Wheals developed on the challenge test with this solution in our patient. Intradermal test with maltose was positive, indicating that elicitation of her type I hypersensitivity was attributable to maltose. Maltose, one of the disaccharides, is present in various diets. Carbohydrates, common food ingredients, are converted into maltose and/or other small glucose polymers before passing beyond the duodenum or upper jejunum.4 However, allergy to dietary maltose has not been reported in the literature. As our patient had no history of food allergy, maltose would not induce allergic reactions in the gut mucosa. Her allergic reaction to injected maltose might be related to the sugar metabolism. All maltose molecules are split into glucose, which has no antigenicity, in the intestine before their absorption into the peripheral circulation. Our case indicates that the same component exhibits different antigenic activity depending on the route of administration. The authors have no conflict of interest to declare.

Bacteroides thetaiotaomicron Starch Utilization Promotes Quercetin Degradation and Butyrate Production by Eubacterium ramulus.

Consumption of flavonoids has been associated with protection against cardiovascular and neurodegenerative diseases. Most dietary flavonoids are subjected to bacterial transformations in the gut where they are converted into biologically active metabolites that are more bioavailable and have distinct effects relative to the parent compounds. While some of the pathways involved in the breakdown of flavonoids are emerging, little it is known about the impact of carbon source availability and community dynamics on flavonoid metabolism. This is relevant in the gut where there is a fierce competition for nutrients. In this study, we show that metabolism of one of the most commonly consumed flavonoids, quercetin, by the gut-associated bacterium Eubacterium ramulus is dependent on interspecies cross-feeding interactions when starch is the only energy source available. E. ramulus can degrade quercetin in the presence of glucose but is unable to use starch for growth or quercetin degradation. However, the starch-metabolizing bacterium Bacteroides thetaiotaomicron, which does not metabolize quercetin, stimulates degradation of quercetin and butyrate production by E. ramulus via cross-feeding of glucose and maltose molecules released from starch. These results suggest that dietary substrates and interactions between species modulate the degradation of flavonoids and production of butyrate, thus shaping their bioavailability and bioactivity, and likely impacting their health-promoting effects in humans.

Active site complementation and hexameric arrangement in the GH family 29; a structure-function study of α-l-fucosidase isoenzyme 1 from Paenibacillus thiaminolyticus.

α-l-Fucosidase isoenzyme 1 from bacterium Paenibacillus thiaminolyticus is a member of the glycoside hydrolase family GH29 capable of cleaving l-fucose from nonreducing termini of oligosaccharides and glycoconjugates. Here we present the first crystal structure of this protein revealing a novel quaternary state within this family. The protein is in a unique hexameric assembly revealing the first observed case of active site complementation by a residue from an adjacent monomer in this family. Mutation of the complementing tryptophan residue caused changes in the catalytic properties including a shift of the pH optimum, a change of affinity to an artificial chromogenic substrate and a decreased reaction rate for a natural substrate. The wild-type enzyme was active on most of the tested naturally occurring oligosaccharides and capable of transglycosylation on a variety of acceptor molecules, including saccharides, alcohols or chromogenic substrates. Mutation of the complementing residue changed neither substrate specificity nor the preference for the type of transglycosylation acceptor molecule; however, the yields of the reactions were lower in both cases. Maltose molecules bound to the enzyme in the crystal structure identified surface carbohydrate-binding sites, possibly participating in binding of larger oligosaccharides.

Reaction chemistry ABC-style

For a time, membrane proteins proved intractable to X-ray crystallography. There were difficulties of overexpression and purification, multiple choices of solubilizing detergent that could only be decided by trial and error, unwillingness to crystallize, and often, poor diffraction from resultant crystals. However, the tide now seems to be turning, and in PNAS, Oldham and Chen (1) present an X-ray crystallography study of the entire WT maltose uptake protein from Escherichia coli, in which four different structures are described at commendable 2.2- to 2.4-A resolution. Maltose uptake protein is a well-characterized model (2) for the large ABC transporter family, members of which occur in all living organisms. ABC transporters, whether exporters or importers, display a common architecture consisting of two transmembrane domains (TMDs) involved directly in transport and two nucleotide binding domains (NBDs) that cooperatively hydrolyze ATP (actually MgATP) to power transport (3). Internationally, numerous researchers study ABC transporters because of their wide involvement in human and plant disease and consequent importance in medicine and agriculture. Maltose uptake protein has subunit structure MalGFK2, with GF forming the TMDs and K2 forming the head to tail NBD dimer, with its two ATP binding sites. Bacterial ABC importers use a binding protein that captures the requisite transport substrate from the periplasm and delivers it to the transporter. In the work by Oldham and Chen (1), maltose binding protein is bound to the MalGFK2 complex in its open state, and the just-delivered maltose molecule is clearly seen in the transport pathway at midmembrane.

Evaluation of Enzymatic Reactors for Large-Scale Panose Production

Panose is a trisaccharide constituted by a maltose molecule bonded to a glucose molecule by an alpha-1,6-glycosidic bond. This trisaccharide has potential to be used in the food industry as a noncariogenic sweetener, as the oral flora does not ferment it. Panose can also be considered prebiotic for stimulating the growth of benefic microorganisms, such as lactobacillus and bifidobacteria, and for inhibiting the growth of undesired microorganisms such as E. coli and Salmonella. In this paper, the production of panose by enzymatic synthesis in a batch and a fed-batch reactor was optimized using a mathematical model developed to simulate the process. Results show that optimum production is obtained in a fed-batch process with an optimum production of 11.23 g/l h of panose, which is 51.5% higher than production with batch reactor.

A Comparative Study of Carboxy Myoglobin in Saccharide−Water Systems by Molecular Dynamics Simulation

Results from room-temperature molecular dynamics simulation on a system containing carboxy-myoglobin, water, and maltose molecules are reported. Protein atomic fluctuations, protein-solvent and solvent-solvent hydrogen bonding have been analyzed and compared to the ones in trehalose-water and sucrose-water systems (Proteins 2005, 59, 291-302). Results help in rationalizing, at a molecular level, the effects of homologues disaccharides on protein structure/dynamics experimentally observed. Furthermore, the effectiveness of disaccharides in bioprotection in terms of peculiar protein-matrix coupling is also discussed.

Kinetic and Structural Analysis of Enzyme Sliding on a Substrate: Multiple Attack in β-Amylase

Beta-amylase (EC 3.2.1.2) is starch-hydrolyzing exo-type enzyme that can catalyze the successive liberation of beta-maltose from the nonreducing ends of alpha-1,4-linked glucopyranosyl polymers. There is a well-known phenomenon called multiple or repetitive attack where the enzyme releases several maltose molecules in a single enzyme-substrate complex. In order to understand it further, we examined the beta-amylase-catalyzed reaction using maltooligosaccharides. The Monte Carlo method was applied for simulation of the beta-amylase-catalyzed reaction including the multiple attack mechanism. Through site-directed mutagenesis, we have successfully prepared a mutant enzyme which may be simulated as a multiple attack action reduced one with retaining significant hydrolytic activity. From the results of X-ray structure analysis of the mutant enzyme, it was clarified that one carboxyl residue plays a very important role in the multiple attack. The multiple attack action needs the force of enzyme sliding on the substrate. In addition, it is important for the multiple attack that the enzyme and substrate have the characteristics of a stable productive substrate-enzyme complex through a hydrogen bond between the nonreducing end of the substrate and the carboxyl residue of the enzyme.

Enantioseparation and Quantitative Analysis of Citalopram by Capillary Electrophoresis with Maltose as the Chiral Selector and Its Separation Mechanism

Chiral separation of citalopram(CIT) was performed by capillary zone electrophoresis (CZE) using maltose as the chiral additive. The effect of the concentration of electrophoretic running buffer, its pH, concentration of maltose, and the applied running voltage were investigated. The optimized conditions were obtained with 20 kV as the running voltage, and a running buffer of 40 % (w/w) maltose in 8.0 × 10 −2 M phosphate (pH 5.0). Good resolution of citalopram enantiomers was achieved and the R s were 2.3 under optimal conditions. The quantitative analysis of citalopram was performed. The linear range of concentration of R-(–)-CIT to their peak areas was 0.05–4.00 mg ml −1. The LOD of the two enantiomers were 4.53 × 10 −2 mg/ml and 4.73 × 10 −2 mg ml −1, respectively. The regression coefficient was more than 0.9978. The interaction between CIT and maltose was studied by fluorescence spectra method and the mechanism of the enantioseparation was also researched. It was proved that the chiral recognition ability of maltose is related to the concentration of maltose. Maltose molecules begin to aggregate to form hydrophobic cavities, when the concentration of maltose exceeds a critical concentration. The enantioselectivity is attributed to the stereo recognition of the cavities formed by aggregating maltose molecules.

Monoclinic crystal form of Aspergillus niger alpha-amylase in complex with maltose at 1.8 angstroms resolution.

Aspergillus niger alpha-amylase catalyses the hydrolysis of alpha-1,4-glucosidic bonds in starch. It shows 100% sequence identity to the A. oryzae homologue (also called TAKA-amylase), three crystal structures of which have been published to date. Two of them belong to the orthorhombic space group P2(1)2(1)2(1) with one molecule per asymmetric unit and one belongs to the monoclinic space group P2(1) with three molecules per asymmetric unit. Here, the purification, crystallization and structure determination of A. niger alpha-amylase crystallized in the monoclinic space group P2(1) with two molecules per asymmetric unit in complex with maltose at 1.8 angstroms resolution is reported. Furthermore, a novel 1.6 angstroms resolution orthorhombic crystal form (space group P2(1)2(1)2) of the native enzyme is presented. Four maltose molecules are observed in the maltose-alpha-amylase complex. Three of these occupy active-site subsites -2 and -1, +1 and +2 and the hitherto unobserved subsites +4 (Asp233, Gly234) and +5 (Asp235). The fourth maltose molecule binds at the distant binding sites d1 (Tyr382) and d2 (Trp385), also previously unobserved. Furthermore, it is shown that the active-site groove permits different binding modes of sugar units at subsites +1 and +2. This flexibility of the active-site cleft close to the catalytic centre might be needed for a productive binding of substrate chains and/or release of products.

Optimization of panose production by enzymatic synthesis using neural networks

Panose is a trisaccharide constituted by a maltose molecule bonded to a glucose molecule by an α-1,6-glycosidic bond. This trisaccharide has the potential to be used in the food industry as a non-cariogenic sweetener and is considered a pre-biotic carbohydrate. Despite the industrial potential applications of panose, a large-scale process for its production is still not available. In this paper, the production of panose by enzymatic synthesis in a batch and a fed-batch reactor was optimized by means of the use of neural network. The optimization of panose has shown that the maximum productivity is obtained when the process is conducted in fed-batch with initial sucrose concentration S 0 = 100 mmol/L, a maltose to sucrose ratio of 5.58 and a feed flow rate of 3000 L/h, yielding 35.3 g/L h of panose, which is 74% higher than the yield that can be obtained through the batch process.

The Roles of Glu186 and Glu380 in the Catalytic Reaction of Soybean β-Amylase

It has previously been suggested that the glutamic acid residues Glu186 and Glu380 of soybean β-amylase play critical roles as a general acid and a general base catalyst, respectively. In order to confirm the roles of Glu186 and Glu380, each residue was mutated to a glutamine residue and the crystal structures of the substrate (E186Q/maltopentaose) and product (E380Q/maltose) complexes were determined at resolutions of 1.6 Å and 1.9 Å, respectively. Both mutant enzymes exhibited 16,000- and 37,000-fold decreased activity relative to that of the wild-type enzyme. The crystal structure of the E186Q/maltopentaose complex revealed an unambiguous five-glucose unit at subsites −2 to +3. Two maltose molecules bind on subsites −2 to −1 and +2 to +3 in the E380Q/maltose complex, whereas they bind in tandem to −2 to −1 and +1 to +2 in the wild-type/maltose complex. The conformation of the glucose residue at subsite −1 was identified as a stable 4C 1 α-anomer in the E380Q/maltose complex, whereas a distorted ring conformation was observed in the wild-type/maltose complex. The side-chain movement of Gln380 to the position of a putative attacking water molecule seen in the wild-type enzyme caused the inactivation of the E380Q mutant and an altered binding pattern of maltose molecules. These results confirm the critical roles played by Glu186 in the donation of a proton to the glycosidic oxygen of the substrate, and by Glu380 in the activation of an attacking water molecule. The observed difference between the backbones of E186Q/maltopentaose and E380Q/maltose in terms of Thr342 suggests that the side-chain of Thr342 may stabilize the deprotonated form of Glu186 after the cleavage of the glycosidic bond.

Crystal structure of a catalytic site mutant of beta-amylase from Bacillus cereus var. mycoides cocrystallized with maltopentaose.

The X-ray crystal structure of a catalytic site mutant of beta-amylase, E172A (Glu172 --> Ala), from Bacillus cereus var. mycoides complexed with a substrate, maltopentaose (G5), and the wild-type enzyme complexed with maltose were determined at 2.1 and 2.0 A resolution, respectively. Clear and continuous density corresponding to G5 was observed in the active site of E172A, and thus, the substrate, G5, was not hydrolyzed. All glucose residues adopted a relaxed (4)C(1) conformation, and the conformation of the maltose unit for Glc2 and Glc3 was much different from those of other maltose units, where each glucose residue of G5 is named Glc1-Glc5 (Glc1 is at the nonreducing end). A water molecule was observed 3.3 A from the C1 atom of Glc2, and 3.0 A apart from the OE1 atom of Glu367 which acts as a general base. In the wild-type enzyme-maltose complex, two maltose molecules bind at subsites -2 and -1 and at subsites +1 and +2 in tandem. The conformation of the maltose molecules was similar to that of the condensation product of soybean beta-amylase, but differed from that of G5 in E172A. When the substrate flips between Glc2 and Glc3, the conformational energy of the maltose unit was calculated to be 20 kcal/mol higher than that of the cis conformation by MM3. We suggest that beta-amylase destabilizes the bond that is to be broken in the ES complex, decreasing the activation energy, DeltaG(++), which is the difference in free energy between this state and the transition state.

Catalytic activities of intracellular dimeric neopullulanase on cyclodextrin, acarbose and maltose.

Multi-substrate specificity of neopullulanase towards cyclodextrin, acarbose and maltose was investigated using a clone originating from Bacillus stearothermophilus IMA6503. The enzyme purified from Escherichia coli harbouring the corresponding nplA gene hydrolysed beta-cyclodextrin (beta-CD) to maltose and glucose. It exhibited substrate preference for beta-CD, starch and pullulan in the proportions of 10.4:1.2:1. The enzyme not only hydrolysed acarbose, an alpha-amylase inhibitor, to a pseudotrisaccharide (PTS) and glucose, but also transferred PTS to glucose, forming isoacarbose. Moreover, it hydrolysed maltose to glucose and transferred the glucose to another maltose molecule to form panose when maltose was present at a low concentration (0.5%) in the reaction solution. The enzyme catalysed condensation between two maltose molecules and subsequent hydrolysis of the resulting 6(2)-O-alpha-maltosyl-maltose to glucose and panose, when maltose concentration was increased to 20%. Neopullulanase was likely to be present in monomer-dimer equilibrium with a molar ratio of 1:9 in 50 mM sodium acetate buffer (pH 6.0). The association-dissociation equilibrium of neopullulanase was shifted to monomerization by KCl. When the content of monomer increased in the reaction mixture, the specific activity towards soluble starch increased to 150%, while that towards beta-CD decreased to 80%. Therefore, multi-substrate specificity of neopullulanase was likely to be modulated by the shift of monomer-dimer association equilibrium.

The role of intra- and intermolecular hydrogen bonds in the formation of β-cyclodextrin head-to-head and head-to-tail dimers. The results of ab initio and semiempirical quantum-chemical calculations

The conformation of a free β-cyclodextrin molecule optimized by the MNDO/PM3 quantum-chemical calculations has C7 symmetry. The “right” orientation of the interglucose hydrogen bonds in β-cyclodextrin, in which the 2-OH groups act as the proton donors and the O atoms of the nearby 3"-OH groups function as the proton acceptors, is advantageous for thermodynamic reasons. The ring of seven H bonds thus formed stabilizes the symmetrical form of β-cyclodextrin. The β-cyclodextrin head-to-head dimer has D7 symmetry and consists of molecules whose 2-OH groups partcipate as proton donors in the formation of fourteen complementary intermolecular hydrogen bonds. The energy of H bonds in the β-cyclodextrin monomer and dimer was estimated to be 1.0--1.4 kcal mol–1. Of the two possible β-cyclodextrin dimers, the “head-to-tail” dimer is more thermodynamically stable. The thermodynamic preference of the right orientation of the inter-glucose H bonds in β-cyclodextrin was confirmed by the MP2/6-31G(d,p)//6-31G(d,p) abinitio calculations for maltose (α-glucodioside). The maltose molecule with inter-glucose H bonds of the type 2-OH→O(3")-H is more stable than the structure with the H-(2)O←H-O(3") orientation of H bonds with a difference of ∼2.7 kcal mol–1. According to the MNDO/PM3 method, the maltose structure with the right H bond orientation is more stable by ∼3.1 kcal mol–1.

Dielectric properties of glucose and maltose solutions

We report molecular dynamics (MD) simulations of aqueous solutions of glucose and maltose. For each sugar, two concentrations were studied. The static and frequency-dependent dielectric properties of the solutions were calculated from MD trajectories of at least 5 ns length and compared to those of pure water. The contributions from the solute, the solvent, and the solute–solvent cross term were analyzed. In addition, for the more dilute glucose and maltose solutions a Voronoi analysis was carried out to distinguish between contributions from the first water shell and from unbound bulk water. The results of the glucose simulations were compared to available experimental data. While the static dielectric constant of the four solutions was found to be very similar to that of pure water, a number of differences could be discerned in the dielectric spectra. These findings for the overall frequency-dependent dielectric susceptibilities were rationalized by a dielectric component analysis. The importance of contributions from cross terms and from the solute depended on solute type (glucose or maltose) and concentration. In particular, we observed a linear correlation between the contribution of the solute–solvent cross term and the total number of hydroxyl groups of the solute (i.e., the number of solute molecules times the number of hydroxyl groups in a glucose or maltose molecule, respectively). The dielectric properties of water in the solutions could be rationalized as the superposition of two contributions, one originating from the bulklike free waters, the other from the waters in the first hydration shell of the saccharides.

Structure of raw starch-digesting Bacillus cereus beta-amylase complexed with maltose.

The crystals of beta-amylase from Bacillus cereus belong to space group P21 with the following cell dimensions: a = 57.70 A, b = 92.87 A, c = 65.93 A, and beta =101.95 degrees. The structures of free and maltose-bound beta-amylases were determined by X-ray crystallography at 2.1 and 2.5 A with R-factors of 0.170 and 0.164, respectively. The final model of the maltose-bound form comprises 516 amino acid residues, four maltose molecules, 275 water molecules, one Ca2+, one acetate, and one sulfate ion. The enzyme consists of a core (beta/alpha)8-barrel domain (residues 5-434) and a C-terminal starch-binding domain (residues 435-613). Besides the active site in the core where two maltose molecules are bound in tandem, two novel maltose-binding sites were found in the core L4 region and in the C-terminal domain. The structure of the core domain is similar to that of soybean beta-amylase except for the L4 maltose-binding site, whereas the C-terminal domain has the same secondary structure as domain E of cyclodextrin glucosyltransferase. These two maltose-binding sites are 32-36 A apart from the active site. These results indicate that the ability of B. cereus beta-amylase to digest raw starch can be attributed to the additional two maltose-binding sites.

Carbohydrate-Arene Interactions Direct Conformational Equilibrium of a Flexible Glycophane in Water.

Water, the flexibility of the maltose molecule, and sugar/arene interactions are responsible for the equilibrium between a folded (I) and nonfolded (II) conformation in a glycophane (III is an intermediate). Glycophanes are cyclodextrin-cyclophane hybrids, which are of interest as models of receptors.