Increased yield of 2-O-α-d-glucopyranosyl-l-ascorbic acid synthesis by α-glucosidase using rational design that regulating the ground state of enzyme and substrate complex

BACKGROUND

α-Glucosidase (AG) is a bifunctional enzyme, it has a capacity to synthesize 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2G) from l-ascorbic acid (L-AA) and low-cost maltose under mild conditions, but it can also hydrolyze AA-2G, which leads to low synthesis efficiency of AA-2G.

MAIN METHODS AND MAJOR RESULTS

This study introduces a rational molecular design strategy to regulate enzymatic reactions based on inhibiting the formation of ground state of enzyme-substrate complex. Y215 was analyzed as the key amino acid site affecting the affinity of AG to AA-2G and L-AA. For the purpose of reducing the hydrolysis efficiency of AA-2G, the mutant Y215W was obtained by analyzing the molecular docking binding energy and hydrogen bond formation between AG and the substrates. Compared with the wild-type, isothermal titration calorimetry (ITC) results showed that the equilibrium dissociation constant (KD ) of the mutant for AA-2G was doubled; the Michaelis constant (Km ) for AA-2G was reduced by 1.15 times; and the yield of synthetic AA-2G was increased by 39%.

CONCLUSIONS AND IMPLICATIONS

Our work also provides a new reference strategy for the molecular modification of multifunctional enzymes and other enzymes in cascade reactions system.

Biphasic alcoholysis coupled with high-speed countercurrent chromatography for high performance on separating phorbol from Croton tiglium Linn extracts

Phorbol is a tetracyclic diterpenoid found in Euphorbia tirucalli, Croton tiglium, and Rehmannia glutinosa, and is nuclear of various phorbol esters. The rapid obtaining of phorbol with high purity highly contributes to its application, such as synthesizing phorbol esters with designable side chains and particular therapeutic efficacy. This study introduced a biphasic alcoholysis method for obtaining phorbol from croton oil by using polarity imparity organic solvents in both phases and established a high-speed countercurrent chromatography method for simultaneous separation and purification of phorbol. The optimized operation conditions of biphasic alcoholysis were a reaction time of 91 min, a temperature of 14°C, and a croton oil-methanol ratio of 1:30 (g:ml). The phorbol during the biphasic alcoholysis was 3.2-fold higher in content than that obtained in conventional monophasic alcoholysis. The optimized high-speed countercurrent chromatography method was using the ethyl acetate/n-butyl alcohol/water at 4.7:0.3:5 (v:v:v) with Na₂ SO₄ at 0.36 g/10 ml as the solvent system, using the mobile phase flow rate of 2 ml/min, the revolution of 800 r/min, under which the retention of the stationary phase was achieved at 72.83%. The crystallized phorbol following high-speed countercurrent chromatography was obtained as high purity of 94%.

[The 40-91 aa sequence of porcine epidemic diarrhea virus ORF3 protein is the key structural domain controlling its location in cytoplasm]

ORF3 protein, the single accessory protein encoded by porcine epidemic diarrhea virus (PEDV), is related to viral pathogenicity. In order to determine the cytoplasmic location signal of PEDV ORF3, we constructed a series of recombinant plasmids carrying full-length or truncated segments of PEDV DR13 ORF3 protein. When the acquired plasmids were transfected into Vero cells, expression and distribution of the EGFP-fused full-length ORF3 protein and its truncated forms in the cells were observed by laser confocal microscopy. The results showed that ORF3 protein or their truncated forms containing 40-91 aa segment including two transmembrane domains were localized in the cytoplasm, whereas ORF3 truncated peptides without the 40-91 aa segment were distributed in the whole cell (in both cytoplasm and nucleus). This suggests that the 40-91 aa is the key structural domain determining cytoplasmic location of PEDV ORF3 protein. The discovery provides reference for further clarifying intracellular transport and biological function of PEDV ORF3 protein.

Near-infrared reflectance spectroscopy-based fast versicolorin A detection in maize for early aflatoxin warning and safety sorting

Aflatoxins (AFs) are potent carcinogens present in numerous crops. Access to accurate methods for evaluating contamination is a critical factor in aflatoxin risk assessment. Versicolorin A (Ver A), a precursor of aflatoxin B₁ (AFB₁), can be used as an indicator for the presence of AFB₁, even when the AF is not yet detectable. Currently employed Ver A detection methods are expensive, time consuming, and difficult to apply to numerous samples. Herein, Ver A was detected via near-infrared spectroscopy. Both quantitative and two-grade sorting methods were set-up using the extreme gradient boosting algorithm coupled with a support vector machine. This two-tiered method obtained a root-mean-square error of prediction value of 3.57 μg/kg for the quantitative model, and an accuracy rate of 90.32% for the sorting approach. This novel method is rapid, accurate, solvent free, requires no sample pretreatment, and detects Ver A in maize, making it convenient for practical use.

Versicolorin A is a potential indicator of aflatoxin contamination in the granary-stored corn

The objective of this study was to evaluate the feasibility of the predictive monitoring of aflatoxin B₁ (AFB₁) under granary conditions, since mycotoxin contamination of the stored grain represents an important issue. Using the storage test, we investigated the relationship between versicolorin A (Ver A, an intermediate in AFB₁ biosynthesis) levels and the levels of aflatoxigenic fungi, and their relationship with aflatoxin production. All samples, except for one, were found to be contaminated with aflatoxigenic fungi using PCR analyses, while their AFB₁ levels were not detectable before the storage test using an enzyme-linked immunosorbent assay (ELISA) method with an LOD of 2 μg/kg. Aflatoxigenic fungi levels were analysed, as well as Ver A levels prior to the accumulation of AFB₁ (Levels were ≥5 μg/kg; the permissible levels of AFB₁ in corn intended for direct consumption are <5 μg/kg (EC)). Statistical analyses demonstrated that aflatoxin levels after both actual storage and safe storage (AFB₁˂5μg/kg) times are significantly correlated with the Ver A levels and the changes in Ver A levels (ΔVer A). Both high and variable Ver A levels were indicative of the vigorous metabolic activity of aflatoxigenic fungi. In contrast, steady Ver A levels showed that aflatoxin production by the fungi was not active. Monitoring Ver A levels and their changes may allow an earlier detection of harmful aflatoxin contamination in the stored grain. Additionally, the toxicity of Ver A should be further examined. The results of our study indicate that the monitoring of Ver A levels, even when the AFB₁ levels are very low, may increase the safety of grain consumption, especially considering Ver A toxicity.

Extraskeletal Ewing's sarcoma: a report of 18 cases and literature review

BACKGROUND AND OBJECTIVE

Extraskeletal Ewing's sarcoma (EES) is a rare, rapidly growing, round-cell, malignant tumor that can develop in the soft tissues at any location. This study was to analyze the clinical features, diagnosis and treatment of EES.

METHODS

Clinical data of 18 patients with EES, treated at between Cancer Center of Sun Yat-sen University between 1995 and 2007, were analyzed.

RESULTS

Of the 18 patients, 13 were male and 8 were female, aged from 8 months to 60 years. Twelve (66.7%) patients were between 5-25 years of age. Eight (44.4%) patients had tumors originated from low extremities.Sixteen patients had masses at their first visit. Sixteen patients were treated by the combined modality therapy, and 2 patients were treated by the single modality therapy. The 1-, 3- and 5- year actuarial survival rates were 82.4%, 64.2% and 32.1%, respectively. The presence of metastatic disease at the time of diagnosis and the mode of treatment were prognostic factors.

CONCLUSIONS

EES is common in adolescent. It often manifests as a localized mass. The combined modality therapy is recommended for this disease. The presence of metastatic disease at the time of diagnosis and the mode of treatment are prognostic factors.

[The primary study on the detection of sterigmatocystin by biologic enzyme electrode modified with the multiwall carbon nanotubes]

Sterigmatocystin (ST), the secondary metabolite of many kinds of filamentous fungi, is a potent carcinogen structurally related to the aflatoxins (AFT). With similar chemical structure, sterigmatocystion behaves much the homogeneous properties to aflatoxins, both of these mycotoxins exhibit similar biological properties due to their bisfuranoid structure. Since the common, and even heavier pollution, found in foods and feeds-stuff, sterigmatocystion is more harmful than aflatoxins. The reported detection methods of sterigmatocystion included the Thin-layer Chromatography, the High-Performance-Liquid Chromatography, the Enzyme-Linked Immunosorbant Assay and the PCR detection to the toxic gene, however studies about both easy and inexpensive electro-chemical methods have not been found. Our previous studies had discovered that Sterigmatocystin (ST) exist similar sensitivity towards aflatoxin-detoxifizyme (ADTZ), which we had isolated from a fungus, as aflatoxin does. In this work, the preliminary study on electrochemical analysis and determination of ST with triplet electrode enzyme-biosensor system (Ag/AgCl as the reference electrode, Pt and Au as the pair and work electrode, respectively) was carried out. Multiwall-carbon-nanotube (MWNT) had been used to increase the electron transportation on electrode. In the research, the Au electrode was modified by MWNT-immobilized ADTZ, and then the voltammertric behavior of ST was studied by means of cyclic voltammogram analysis and different pulse analysis. Autoprobe CP Research Atomic Force Microscope and TECNAI 10 Transmission Electron Microscope, had been used to detect the MWNT as well as the surface of MWNT-modified ADTZ. The voltammertric behavior of ST was studied by means of cyclic voltammogram analysis and different pulse analysis. The results show that the red-ox peak potential of ST is at the point of -600 mV, the linear detection range is from 8.32 x 10(-5) to 66.56 x 10(-5) mg/mL, the detection limit is at 8.32 x 10(-5) mg/mL, and the response time is 10 seconds. This study provided a good basic work for further research.

[Characterization of immobilized aflatoxin-detoxizyme]

Aflatoxins, found in contaminated food, are potent hepatocarcinogen. The aflatoxin-detoxiczyme (ADTZ) isolated from the edible fungus Armillariella sp., detoxifies aflatoxin B1 (AFB1). This paper reports on the characterization of immobilized ADTZ using a hydrophobic adsorption method. The ADTZ was isolated from cryo-homogenated fungus, previously cultivated at 24 - 28 degrees C for 20 - 30 days, using n-alkyl amino-agar beads. Various adsorption conditions of the enzyme to n-alkyl or n-octyl amino-agar beads were carried out. The effects of enzyme immobilization on different alkyl amino-agar beads, at different pH values (5.5 - 7.5), at different temperature (20 - 40 degrees C) and at different salt concentrations were investigated. The enzyme activity was measured at OD360 by reacting 133.3 ng/mL of AFB1 at 30 degrees C for 30 min with the immobilized ADTZ. The Km value of the immobilized enzyme, determined using Schematic Linewearver-Burk plot, is 3.308 x 10(-3) mol/L, lower than that of free enzyme, which is 2.16 x 10(-6) mol/L. This indicated the affinity of the detoxiczyme to AFB1 decreased after immobilization. The immobilized enzyme activity in oil-phase (n-hexane) was also studied with different concentration of water. After the treatment of the immobilized ADTZ, the toxin no longer causes liver toxicity in the rat toxicity test, no longer causes mutagenicity in Ames test and is no longer toxic in the chicken embryo test. Results also indicated that the pH stability, the thermostability and the freezing stability of ADTZ were improved after the immobilization.

[Humoral and cellular immune responses to retinal S-antigen in uveitis patients]

Humoral and cellular immune responses to purified S-Ag were determined in 73 patients with anterior-, intermediate- and pan-uveitis and in 55 healthy subjects by ELISA and leucocyte migration inhibition test. The positive rates of humoral immune response to S-Ag in patients and controls were comparable; however, the positive rate of cellular immune response to S-Ag in the patients (54.6%) was significantly higher than that in the controls (3.3%), and that in pan-uveitis patients (69.4%) was significantly higher than in patients with anterior uveitis (15.4%), highly suggesting that the cellular immune response to S-Ag was involved in the onset of uveitis, especially when the choroid and retina were affected. The breakdown of anterior chamber associated immune deviation and abnormal expression of intraocular MHC-II antigens may contribute to the development of cellular immune response. More studies are needed.

Design of intracavitary microwave applicators for the treatment of uterine cervix carcinoma

A 915 MHz intracavitary applicator was designed to heat tumours in the cervical and upper vaginal regions. The applicator has a 3.5-turn helical coil wound around the distal 19 mm of a dielectric rod 43 mm long and 30 mm in diameter. For treating uterine cancer, a 2450 MHz, 4 mm diameter helical applicator was made by replacing 6 cm of the outer conductor of a coaxial cable with six turns of copper wire soldered to the outer conductor. The heating patterns were determined thermographically in a muscle phantom. The maximum heating rates were 0.42 and 0.83 degrees C/W-min, respectively, for the 915 and 2450 MHz applicators. Intracavitary temperature distributions in the upper vagina, cervix and uterus were measured at the surface of the applicators with thermocouples. The average temperature was 46.0 +/- 2.1 degrees C (S.D.) at mid-tumour and 44.5 +/- 0.8 degrees C at the tumour periphery. The maximum temperature, up to 51.5 degrees C, was measured at the surface of the cervical applicator. The majority of the patients (28/30) tolerated the investigational treatment without burns or pain. Rectal temperatures were also monitored. The location of the hot-spot (40.7 degrees C) in the rectum, 5-7 cm above the anus, corresponded to the tip of the cervical applicator (47.1 degrees C).

[A study of Kirby-Bauer method of antimicrobial sensitivity test and resistant plasmid assay with 486 strains of Shigella isolated clinically]

486 cases of bacillary dysentery admitted to an army hospital during the peak season (July to September) from 1986 to 1988 were studied. The pathogens in 452 cases were tested for antimicrobial sensitivity with 14 kinds of antibiotics by using Kirby-Bauer method recommended by WHO. The results showed that the number of antibiotics to which the dysentery bacteria became resistant had increased. In 1986 the number was 9, while in 1987 and 1988 it increased to 12 and 13 respectively. Among the resistant strains of bacteria, 331 had been assayed for resistant plasmids. 88.8% was positive with more than three resistant plasmids. The result of antimicrobial sensitivity test coincided well with that of resistant plasmid assay.

[Antibodies against alpha, beta, and gamma crystallins in human serum]

Serum antibodies against alpha, beta, and gamma crystallins in 79 normal subjects and 38 patients with senile cataract were determined by ELISA, with the result that the presence of the antibodies was related to age, not to sex, and the rate of presence in patients with senile cataract did not differ from that of controls. The relationship between the presence of the antibodies and senile cataract was discussed.

Specific antitumor immunologic reactivity in patients with retinoblastoma

Retinoblastoma antigen (RbAg) and retinal tissue antigen (RAg) were made from allogeneic retinoblastoma tissues and normal retinal tissue using the 3M KCl method. We have examined leukocyte migration inhibition test (LMIT) and enzyme-linked immunosorbent assay (ELISA) to RbAg and RAg in normal controls and the patients with retinoblastoma, including two spontaneously regressed cases. In LMIT, six out of the 11 patients tested against RhAg showed positive reactivity, in which 4 cases reacted only with RbAg, but not with RAg. All nine control subjects had negative reactivity to the two antigens. In ELISA, 40% of the retinoblastoma patients and 5.56% in normal controls showed positive reaction against RbAg. It was suggested that not only retinal antigens but also retinoblastoma specific antigens present in human retinoblastoma cells. The results also suggested that patients with retinoblastoma and those with spontaneous regression of Rb had both cell-mediated immunologic reactivity and humoral immune response toward retinoblastoma antigen in vitro. These immune responses to RbAg may be responsible for spontaneous regression of retinoblastoma.

Humoral and cellular immune responses to lens protein in patients with congenital cataract

In order to understand the immune responses to lens protein in patients with congenital cataract, the passive hemagglutination assay for humoral immunity and the leukocyte migration test for cellular immunity to lens protein were performed on 43 patients with congenital cataract and 30 healthy persons served as control. The results showed that there was no significant difference in the incidence of humoral immune responses to lens protein between patients with congenital cataract and the controls (P greater than 0.05), but the incidence of cellular immune responses to lens protein in patients with congenital cataract was higher than that of the controls (P less than 0.005). The results of this study suggested that during the development of congenital cataract, lens protein leaked into the aqueous humour and entered the systemic circulation, sensitizing lymphocytes and producing cellular mediated immune responses. Further investigation is necessary to determine whether there is any relationship between the immune responses to lens protein and the formation of congenital cataract.