A novel biosensor for aflatoxin B1 detecting has been reported. The biosensor electrode for AFB1 detecting was assembled by immobilized aflatoxin-oxidoreductase using open-ended multi-walled carbon nanotubes as matrix. Its linear range was between 0.16μM and 3.2μM. And if the specific anti-aflatoxin B1 antibody and aflatoxin oxidoreductase were both immobilized on the electrode with Multi-Walled carbon nanotubes, the detection limit of the modified electrode could be 16 nM with a 10 times improved sensitivity. The aflatoxin enzyme biosensor assembled this way strode one step forward its practical application.

The expression cDNA library of A. tabescens was constructed by SMART technique, which useλTriplEx2 as a vector. The titer and the percentage of the constructed library were about 1.0 × 106pfu/mland 98.3% respectively, and the titer and the capacity of the amplified library were about 3.1 × 108pfu/mland 4.2 × 1010. The library was used to provide expressed sequence tags (ESTs). 147 Expressed SequenceTaqs (ESTs) were gained from 176 clones, which were selected randomly and sequenced at the 5'end. Thesequences were submitted to the EMBL database. Blasting the sequences in the GenBank, 43 of them werefound that they have significant similarity with data in GenBank. EST AJ620046 was has significantsimilarity with the arabinosidase of Bacteroides thetaiotaomicron. Using SMART-RACE a full-length cDNA ofAJ620046 was successfully obtained. In order to initially characterize the biochemical properties ofAJ620046, the ORF of AJ620046 named AF was cloned and expressed in Pichia Pastoris yeast.Recombinant pHIL-S1-AF constructed by inserting AF into pHIL-S1 was transformed into Pichia PastorisGS115. Preliminary experiments indicated that AJ620046 was expressed as a 32 kDa protein in recombinantyeast.

Aim The purpose of this study was to compare the effect of AA、15-HETE、15-KETE and 8(S),15(S)-DiHETE on hypoxic and normoxic rabbit pulmonary arterial rings and to discuss their roles in the formation of PA hypertension.Methods Twelve neonatal rabbits were randomly divided into two groups(n=6):the normoxic group breathing fresh gas(FiO_2 =21%) and the hypoxic group breathing hypoxic gas(FiO_2=10%).After 9 days,they were anesthetized with pentobarbital sodium,and the chest was opened for removal of the heart and lungs en bloc,then PA rings(0.5~1.5 mm in diameter and 3 mm length) were prepared.We used tension studies of PA rings to observe the effect of AA、15-HETE、15-KETE and 8(S),15(S)-DiHETE on hypoxic and normoxic rabbit pulmonary arterial rings.Results ① AA、15-HETE、15-KETE and 8(S),15(S)-DiHETE constricted normoxic rabbit PA rings in a dose-dependent manner,respectively.Constriction of normoxic rabbit PA rings induced by 15-KETE、8(S),15(S)-DiHETE was significant,but that of AA、15-HETE wasn′t significant.② AA、15-HETE、15-KETE and 8(S),15(S)-DiHETE increased hypoxic rabbit PA rings' tension.Constriction of AA、15-HETE on rabbit PA rings in hypoxic group was significantly greater than that of normoxic group(P0.05).③ Constriction of 15-KETE on rabbit PA rings in normoxic group was significantly greater than that of hypoxia group(P

Aim To investigate the effect of 15-ketoeicosatetraenoic acid(15-KETE)and its mechanism through ion channels on rat isolated pulmonary arterial rings by using organ bath technique.Methods Sixteen healthy Wistar rats weighing 220?20 g were divided into two groups(n=8): normoxia group breathing fresh air(FiO_2=21%) and hypoxia group breathing hypoxic air(FiO_2=10%) in a hypoxic box.Pulmonary arteries(PA)were extracted after 9 d and cut into rings(0.5~1.0 mm in diameter and 3 mm in length) for organ bath experiments.Results(1) With increasing concentration from 0 to10~(-6) mol?L~(-1),15-KETE increased PA rings tension gradually in a dosedependent fashion;(2) 4-aminopyridine(2 mmol?L~(-1)),a Kv channel blocker significantly decreased constriction of rat isolated PA rings induced by 15-KETE,and results were similar in two groups;(3) The K_(ATP) channel blocker glyburide(10~(-6)6 mol?L~(-1)) and the BK_(Ca) channel blocker tetraethylammonium(10 mmol?L~(-1)) did not affect constriction of rat isolated PA rings induced by 15-KETE;(4) The BKCa channel blocker nifedipine(10~(-6) mol?L~(-1)) and Ca~(2+)-free Krebs solution significantly decreased constriction of rat isolated PA rings induced by 15-KETE.Conclusion Kv channels play a role in constriction of PA induced by 15-KETE;L-type Ca~(2+) channel blocker and extracellular calcium ion also influence constriction of isolated PA rings induced by 15-KETE.

The experiment was conducted by directed evolution strategy (error-prone PCR) to improve the activity of aflatoxin detoxifzyme with the high-throughput horse radish peroxidas and recessive brilliant green (HRP-RBG) screening system. We built up a mutant library to the order of 10(4). Two rounds of EP-PCR and HRP-RBG screening were used to obtain three optimum mutant strains A1773, A1476 and A2863. We found that mutant A1773 had upper temperature tolerance of 70 degrees C and that its enzyme activity was 6.5 times higher than that of the parent strain. Mutant strains A1476 worked well at pH 4.0 and its enzyme activity was 21 times higher than that of the parent strain. Mutant A2863 worked well at pH 4.0 and pH 7.5, and its enzyme activity was 12.6 times higher than that of the parent strain. With DNA sequencing we found that mutant A1773 revealed two amino acid substitutions, Glu127Lys and Gln613Arg. Mutant A1476 revealed four amino acid substitutions: Ser46Pro, Lys221Gln, Ile307Leu and Asn471lle. Mutant A2863 revealed four amino acid substitutions: Gly73Ser, Ile307Leu, Va1596Ala and Gln613Arg. The results provided a useful illustration for the deep understanding of the relationship between the function and structure of aflatoxin detoxifzyme.
Aflatoxin B1 ; antagonists & inhibitors ; chemistry ; Amino Acid Substitution ; Directed Molecular Evolution ; Enzyme Activation ; Enzyme Stability ; Multienzyme Complexes ; genetics ; metabolism ; Mutant Proteins ; genetics ; metabolism ; Point Mutation ; Polymerase Chain Reaction ; methods ; Protein Engineering

We used reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE) techniques to obtain the full-length cDNA of beta-mannanase (EC 3.2.1.78) from Armillariella tabescens EJLY2098 (an edible fungus). Sequence analysis of the 1481 bp full-length cDNA encoding 445 amino acid residues indicated that the gene contained two structural domains, cellulose-binding domains (CBD) and glycoside hydrolase family 5 (GHF5) domains, other than the conserved beta-mannanase domain. Thus, we classified this gene as a member of glycoside hydrolase family 5. Next, we cloned a 1308 bp fragment encoding the beta-mannanase mature peptide (re-atMAN47) into the expression vector pPICZalphaA and expressed it in Pichia pastoris. The yield was 440 mg/L. Enzyme activity reached a maximum of 1.067 IU/mL after 72 h of methanol induction. The re-atMAN47 had an optimal temperature of 60 degrees C and an optimal pH of 5.5. It manifested broad thermostability from 30 degrees C-65 degrees C, and was stable between pH 4.5-7.0. This study represents the first record of a beta-mannanase from Armillariella tabescens EJLY2098 and provides a new source of carbohydrate hydrolysis enzyme with good biosafety, thermostability and wide pH stability. It is a good approach for the industrial needs of feed, food and pharmaceutical manufacturers.
Armillaria ; classification ; enzymology ; genetics ; Cloning, Molecular ; Enzyme Stability ; Pichia ; genetics ; metabolism ; Recombinant Proteins ; biosynthesis ; genetics ; Sequence Analysis, DNA ; beta-Mannosidase ; biosynthesis ; chemistry ; genetics

A sensitive electrochemical biosensor based on Aflatoxin-Oxidase (AFO) was developed for detection of sterigmatocystin (ST). The enzyme was immobilized on chitosan-single-walled carbon nanotubes (CS-SWCNTs) hybrid film, which attached to the poly-o-phenylenediamine (POPD)-modified Au electrode. The fabricated procedures of the biosensor were characterized with atomic force microscopy (AFM), fourier transform-infrared spectroscopy (FT-IR), and electrochemical impedance spectroscopy (EIS). The cyclic voltammetric results of the biosensor indicated that AFO exhibited a surface-controlled and quasi-reversible electrochemical redox behavior with a formal potential of -0.436 V (vs. Ag/AgCl) in 0.1 mol/L PBS (pH 7.0), which resulted from the direct electron transfer between entrapped AFO and the underlying electrode. The enzymatic electrode exhibited an excellent electrocatalytic response to ST. The linear range of ST determination was from 10 ng/mL to 310 ng/mL with correlation coefficient of 0.997, the detection limit was 3 ng/mL (S/N=3), and the response time was less than 10 seconds. The apparent Michaelis-Menten constant (K(M)app) was estimated to be 7.13 micromol/L. The biosensor had the advantages of good repeatability and stability, remaining 85.6% of its original current value after storage at 4 degrees C for a month, and the RSD for 11 replicate determination of 20 ng/mL ST was 3.9%. This AFO/CS-SWCNTs/POPD/Au modified electrode showed high selectivity and sensitivity in real sample analysis, giving values of recovery in the range of 87.6%-105.5%. The proposed method can be applied to the determination of ST in real samples with satisfactory results.
Aflatoxins ; Biosensing Techniques ; methods ; Chitosan ; chemistry ; Electrons ; Nanotubes, Carbon ; Oxidation-Reduction ; Oxidoreductases ; Phenylenediamines ; chemistry ; Sterigmatocystin ; analysis

We has studied the feasibility of preventing protein from denature during covalent immobilization by "conformation memory", which was achieved by freeze-drying under enzyme active conformation and cross-linked with carrier under micro-aqueous media (MAM). Horseradish peroxidase (HRP) and chitosan beads have been used as the model enzyme and carrier. The MAM consisted of 99% dioxane and 1% water. We compared the immobilized HRP under MAM with that under traditional aqueous solvent, found that the optimum temperature of both was raised to 60 degrees C, and the optimum pH was 6.5. However, the MAM-immobilized HRP had shown less activity loss during usage and six times higher activity than that immobilized under aqueous solvent. After 30 min incubation at 70 degrees C, the MAM-immobilized HRP remained 75.42% activity while the aqueous-media-immobilized enzyme only 15.4%. The MAM-immobilized HRP has shown a better operation stability with 77.69% residue activity after 5 times of repeat operation while the aqueous-media-immobilized enzyme only 16.67%. In addition, the MAM-immobilized HRP had also shown more advantages when used in phenol removal. We constructed enzyme electrodes (CS-HRP-SWCNTs/Au) to further display the different properties of the two immobilized HRP. MAM-immobilized HRP-electrode has shown two times stronger response signal to H2O2 than that immobilized under aqueous media, which indicated a better enzyme activity of MAM-immobilized HRP. Our research demonstrated that the conformation memory, to some extent, did contribute to preventing protein from denaturing when use HRP as a model, and it is feasible to immobilize enzyme by covalent cross-linking method under micro-aqueous media.
Chitosan ; chemistry ; Enzyme Stability ; Enzymes, Immobilized ; metabolism ; Freeze Drying ; Horseradish Peroxidase ; chemistry ; metabolism ; Protein Conformation ; Solvents

Firstly, We used error-prone PCR to induce mutations on Armillariella tabescens MAN47 beta-mannanase gene, Secondly, we cloned the mutated fragments into secreted expression vector pYCalpha, Then the recombinant plasmids were transformed into Saccharomyces cerevisiae BJ5465 after amplified and extracted in DH5alpha cells. Through three cycles of error-prone PCR we built a mutant database, Then we screened one optimum (named M262) from about 104 mutants. The evoluted MAN47 beta-mannanase displayed both higher thermal stability and activity than wide type. The evoluted enzyme M262 retained high activity after treatment at 80 degrees C for 30 min, whereas, the wild type nearly lost activity under this condition. Meanwhile, the activity of M262 can reach to 25 U/mL, which is 4.3 times as wide type under optimum temperature. In addition, pH stability and pH range of evoluted enzyme M262 were both improved compared with wild-type enzyme. The optimum pH was estimated to be similar to that of wild-type enzyme. The sequence comparison illustrated that there were three nucleotide substitutions (T343A/C827T/T1139C) which carried corresponding amino acid changes (Ser115Thr/Thr276Met/Val380Ala). According to homologous modeling by SWISS-MODEL Repository, three mutated amino acids located at the sixth amino acid of the fourth beta-sheet, the first amino acid of the sixth alpha-helix, the turn between the tenth and eleventh beta-sheet, respectively.
Armillaria ; classification ; enzymology ; genetics ; Directed Molecular Evolution ; Enzyme Stability ; Escherichia coli ; enzymology ; genetics ; Hot Temperature ; Mutant Proteins ; genetics ; metabolism ; Point Mutation ; Polymerase Chain Reaction ; methods ; Protein Engineering ; Recombinant Proteins ; genetics ; metabolism ; Saccharomyces cerevisiae ; enzymology ; genetics ; beta-Mannosidase ; chemistry ; genetics ; metabolism

Activity losing during the covalent immobilization of enzyme is a serious problem. Here we studied organic phase immobilization by using glucose oxidase (GOD) as a model. After lyophilized at optimum pH, GOD is covalently immobilized onto glutaraldhyde-activated chitosan microsphere carrier under the condition of water, 1, 4-dioxane, ether and ethanol separately. The special activities, enzyme characterization and kinetic parameters are determined. Results show that all of the organic phase immobilized GODs have higher special activities and larger K(cat) than that of aqueous phase. Under the conditions of 0.1% of glutaraldehyde, 1.6% moisture content with 80 mg of GOD added to per gram of carrier, 2.9-fold of the special activity and 3-fold of the effective activity recovery ratio were obtained, and 3-fold of the residue activity was demonstrated after 7 runs when compares 1, 4-dioxane phase immobilized GOD with water phase immobilized one. In addition, kinetic study shows that 1,4-dioxane immobilized GOD (Km(app) = 5.63 mmol/L, V(max) = 1.70 micromol/(min x mg GOD), K(cat) = 0.304 s(-1) was superior to water immobilized GOD (Km(app) = 7.33 mmol/L, V(max) = 1.02 micromol/(min x mg GOD), K(cat) = 0.221 s(-1)). All above indicated GOD immobilized in proper organic media presented a better activity with improved catalytic performance. Organic phase immobilization might be one of the ways to overcome the conformational denature of enzyme protein during covalent modification.
Chitosan ; chemistry ; Dioxanes ; chemistry ; Enzymes, Immobilized ; chemistry ; Freeze Drying ; Glucose Oxidase ; chemistry ; Kinetics ; Microspheres