[Association study between the KCNE family gene polymorphisms of potassium channel gene and the susceptibility of atrial fibrillation]

Objective: To investigate the relationship between KCNE family gene polymorphisms of potassium channel gene and the susceptibility of atrial fibrillation (AF). Methods: In the case-control study, a total of 648 subjects were studied, of which 338 patients with atrial fibrillation were selected from the Department of Cardiovascular Medicine, Putuo Hospital Affiliated to Shanghai University of Traditional Chinese Medicine from January 2019 to December 2019, and 310 healthy people were selected from the physical examination population during the same period. DNA sequencing technology and polymerase chain reaction (PCR) were used to detect the genotype and allele frequency of rs1805127 of KCNE1, rs9984281 of KCNE2, rs9516, rs626930 of KCNE3 and rs12621643 of KCNE4. Results: The ages of subjects in atrial fibrillation group and control group were (69±13) and (73±8) years, respectively (P=0.077). Men subjects accounted for 57.70% (195 men) and 40.00% (124 men) in the two groups, respectively (P=0.092). The distribution frequencies of the allele C at rs1805127 of gene KCNE1, the allele A at rs9984281 of gene KCNE2 and the allele G at rs12621643 of gene KCNE4 were significantly different between groups (P<0.05). After adjustment for sex, smoking, hypertension, cardiac insufficiency and other factors, it was found that the increase in the frequency of the above three loci would increase the risk of atrial fibrillation (rs1805127 OR=7.064, 95%CI:1.559-31.997; rs9984281 OR=4.210, 95%CI:1.118-15.850; rs12621643 OR=2.679, 95%CI:1.025-6.998). Conclusion: The rs1805127 of KCNE1, the rs9984281 of KCNE2,the rs12621643 of KCNE4 were significantly associated with the susceptibility to atrial fibrillation.

[Screening and analysis of prognostic factors of repairing single missing tooth by autotransplantation of teeth]

Objective: To screen and analyze the factors affecting the prognosis of replacing single missing tooth by autograft tooth, so as to provide reference for clinical judgment of surgical prognosis. Methods: A total of 176 patients (188 teeth) underwent autotransplantation of teeth in the Department of Oral & Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University from January 2017 to December 2019, including 85 teeth of males and 103 teeth of females were involved. The age was (33.0±9.8) years (16-65 years). The possible factors affecting the prognosis of replacing single missing tooth by autograft tooth were summarized and grouped, and the clinical and imaging data were recorded and judged. The surgical records and photographic data from the patients' previous medical records were retrospectively analyzed. The survival analysis method was used for statistical analysis to screen out the factors affecting the cumulative survival rate of transplanted teeth. Results: The 5-year cumulative survival rate of 188 transplanted teeth was 88.4%. Univariate Log-Rank analysis showed that age (P<0.001), sex (P=0.008), smoking (P<0.001), position of recipient area (P<0.001), height of alveolar bone in recipient area (P<0.001), time of donor tooth in vitro (P<0.001), use of donor model (P<0.001) and initial stability (P<0.001) were significantly correlated with cumulative survival rate of transplanted teeth. Multivariate Cox proportional hazard regression analysis showed that smoking (β=-2.812, P=0.049), alveolar bone height (β=1.521, P=0.020), donor time (β=-2.001, P=0.019), use of donor model (β=1.666, P=0.034) and initial stability (β=-1.417, P=0.033) were significantly correlated with the cumulative survival rate of transplanted teeth. Conclusions: The prognosis of autogenous tooth transplantation can be predicted by smoking, height of alveolar bone in recipient area, time of donor teeth in vitro, use of donor model and initial stability. Good prognosis of transplanted teeth can be obtained by using donor model during operation, reducing the time of donor teeth in vitro, taking effective methods to restore alveolar bone height, maintaining good initial stability, and good oral health education after operation.

[Clinical observation of three-dimensional printing donor tooth model in peri-operative period of autotransplantation of tooth]

Objective: To prepare a three-dimensional (3D) printing donor tooth model and to observe its application in the peri-operative period. Methods: In part one, 192 cases (2017.9-2019.8) from Department of Oral & Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University ［107 males and 85 females, age (34.2±10.7) years］ which need autotransplantation of teeth (ATT) were collected. Whether the donor teeth can be completely extracted was predicted through clinical and imaging examination (first prediction). The second prediction was supplemented by the three-dimensional printing model of the donor teeth. Each of the prediction was compared with the actual results and the coincidence rate was calculated. In part two, 64 cases (2017.9-2019.8) from Department of Oral & Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University ［28 males, 36 females, age (30.2±8.3) years］ which need ATT were randomly divided into the model group and the donor group. The time of alveolar fossa preparation, time of donor tooth in vitro, times of trial implantation and time of pulptomy and root canal location were recorded respectively. Results: In part one, the coincidence rate between the second prediction and the actual results ［97.4%(187/192)］ was significantly higher than that of the first prediction ［93.2%(179/192)］ (P<0.05). In part two, the preparation time of the alveolar fossa in the maxillary and mandibular were (18.8±4.6) and (22.7±3.4) min, the time of the teeth in vitro were (3.0±0.6) and (2.1±0.6) min, the times of trial implantation were (1.3±0.8) and (1.0±0.9), and the time of pulpotomy and root canal location were (4.3±0.6) and (4.0±0.5) min. All values in the model groups were better than those in the donor group (P<0.05). Conclusions: The 3D printing model is accurate. It can be used in autogenous tooth transplantation to shorten the preparation time of alveolar fossa and time of donor tooth in vitro, and reduce the times of trial implantation of donor teeth, and to help to improve the prediction accuracy of complete extraction of donor teeth and the time of pulpotomy and root canal location.

Biological Toxicity Effects of Soil Pollution Caused by Galvanized Wastewater Based on Vibrio Qinghaiensis sp.-Q67

Objective To establish a rapid diagnosis method for the biological toxicity of soil, accurately and rapidly evaluate the toxicity of contaminated sites and identify the dominant pollutants. Methods Take the soil pollution of a galvanized factory as an example, while the metal concentration level was analyzed and detected, a rapid biological toxicity detection method based on the acute toxicity test of luminescent bacteria （Vibrio qinghaiensis sp.-Q67） was established, and the dominant pollutants were identified by stepwise multiple regression. Results The pollutants came from wastewater and metal plating fragments directly discharged from the manufacturing line of the factory. The concentration of those pollutants was correlated with the acute toxicity of Vibrio qinghaiensis sp.-Q67. The dominant pollutants in the study were zinc （Zn）, aluminum （Al） and copper （Cu）. Conclusion The luminescent bacteria toxicity test method based on Vibrio qinghaiensis sp.-Q67 can conveniently and rapidly assess the degree of toxic damage of polluted soil and identify the dominant pollutants and can be applied to the acute toxicity evaluation of polluted soil.

Effect of JJYMD-C, a novel synthetic derivative of gallic acid, on proliferation and phenotype maintenance in rabbit articular chondrocytes in vitro

Tissue engineering encapsulated cells such as chondrocytes in the carrier matrix have been widely used to repair cartilage defects. However, chondrocyte phenotype is easily lost when chondrocytes are expanded in vitro by a process defined as “dedifferentiation”. To ensure successful therapy, an effective pro-chondrogenic agent is necessary to overcome the obstacle of limited cell numbers in the restoration process, and dedifferentiation is a prerequisite. Gallic acid (GA) has been used in the treatment of arthritis, but its biocompatibility is inferior to that of other compounds. In this study, we modified GA by incorporating sulfamonomethoxine sodium and synthesized a sulfonamido-based gallate, JJYMD-C, and evaluated its effect on chondrocyte metabolism. Our results showed that JJYMD-C could effectively increase the levels of the collagen II, Sox9, and aggrecan genes, promote chondrocyte growth, and enhance secretion and synthesis of cartilage extracellular matrix. On the other hand, expression of the collagen I gene was effectively down-regulated, demonstrating inhibition of chondrocyte dedifferentiation by JJYMD-C. Hypertrophy, as a characteristic of chondrocyte ossification, was undetectable in the JJYMD-C groups. We used JJYMD-C at doses of 0.125, 0.25, and 0.5 µg/mL, and the strongest response was observed with 0.25 µg/mL. This study provides a basis for further studies on a novel agent in the treatment of articular cartilage defects.

Current noise in three-terminal hybrid quantum point contacts

We investigate the current noise of three-terminal hybrid structures at arbitrary bias voltages. Our results indicate that the noise can be a useful tool to extract dynamical information in multi-terminal hybrid structures. The zero-frequency noise is sensitive to the coupling with a normal lead. As a result, the characteristic multiple-step structure of the noise Fano factor due to multiple Andreev reflection will be suppressed as we increase this coupling. In addition, the internal dynamics due to processes of Andreev reflection and multiple Andreev reflection raises rich features in the noise spectrum corresponding to the energy differences of various dynamical processes.

Disorder effect on the transport properties of graphene quantum well structures

We study the disorder effect on the transport properties of graphene quantum well structures using a phenomenological statistical model. By adopting the transfer matrix method combined with a Monte Carlo averaging procedure, we observe transitions from ballistic transport to the diffusive limit. It is found that the transmission probability of incident electrons is sensitive to the disorder effect. The significance of the disorder effect depends on the incident angle of the electrons. For normal incidence, the perfect transmission due to the Klein tunneling remains robust against the disorder effect. For tilted incidence, the transmission possibility can be suppressed. In particular, we found that the transmission probability for electrons with a very small angle, i.e. the wavevector along the transport direction is zero in the barrier, can be greatly suppressed. As a result, abrupt dips at these wavevectors emerge in the transmission spectrum.

Ferritin heavy chain-mediated iron homeostasis and subsequent increased reactive oxygen species production are essential for epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) plays a critical role in tumor progression. To obtain a broad view of the molecules involved in EMT, we carried out a comparative proteomic analysis of transforming growth factor-beta1 (TGF-beta1)-induced EMT in AML-12 murine hepatocytes. A total of 36 proteins with significant alterations in abundance were identified. Among these proteins, ferritin heavy chain (FHC), a cellular iron storage protein, was characterized as a novel modulator in TGF-beta1-induced EMT. In response to TGF-beta1, there was a dramatic decrease in the FHC levels, which caused iron release from FHC and, therefore, increased the intracellular labile iron pool (LIP). Abolishing the increase in LIP blocked TGF-beta1-induced EMT. In addition, increased LIP levels promoted the production of reactive oxygen species (ROS), which in turn activated p38 mitogen-activated protein kinase. The elimination of ROS inhibited EMT, whereas H2O2 treatment rescued TGF-beta1-induced EMT in cells in which the LIP increase was abrogated. Overexpression of exogenous FHC attenuated the increases in LIP and ROS production, leading to a suppression of EMT. We also showed that TGF-beta1-mediated down-regulation of FHC occurs via 3' untranslated region-dependent repression of the translation of FHC mRNA. Moreover, we found that FHC down-regulation is an event that occurs between the early and highly invasive advanced stages in esophageal adenocarcinoma and that depletion of LIP or ROS suppresses the migration of tumor cells. Our data show that cellular iron homeostasis regulated by FHC plays a critical role in TGF-beta1-induced EMT.

Comparative proteomic analysis of colon cancer cells in response to oxaliplatin treatment

Colon cancer is one of the most common malignancies in the world. Oxaliplatin, a third-generation platinum compound, is widely used in clinical chemotherapy of colon cancer. Although the mechanisms of the antitumor effect of Oxaliplatin have been investigated in recent years, the proteomic changes that are associated with the cellular response to this compound are poorly understood. In this study, we performed a comparative proteomic analysis to survey the global changes in protein expression levels after Oxaliplatin treatment in three colon cancer cell lines: HT29, SW620, and LoVo. Two-dimensional gel electrophoresis coupled with MALDI-TOF/TOF mass spectrometry revealed 57, 48, and 53 differentially expressed proteins in the three cell lines (HT29, SW620 and LoVo, respectively) after Oxaliplatin treatment. Of these proteins, 21 overlapped among all three cell lines. These overlapping proteins participate in many cellular processes, such as apoptosis, signal transduction, transcription and translation, cell structural organization, and metabolism. Additionally, the expression levels of ezrin (EZRI), heat-shock protein beta-1 (HSPB1), translationally controlled tumor protein (TCTP), and cell division control protein 2 homolog (CDC2) were confirmed by immunoblotting. This is the first direct proteomic analysis of Oxaliplatin-treated colon cancer cells. Several interesting proteins that we found warrant further investigation owing to their potential significant functions in the antitumor effect of Oxaliplatin.

Identification of candidate prostate cancer biomarkers in prostate needle biopsy specimens using proteomic analysis

Although serum prostate specific antigen (PSA) is a well-established diagnostic tool for prostate cancer (PCa) detection, the definitive diagnosis of PCa is based on the information contained in prostate needle biopsy (PNBX) specimens. To define the proteomic features of PNBX specimens to identify candidate biomarkers for PCa, PNBX specimens from patients with PCa or benign prostatic hyperplasia (BPH) were subjected to comparative proteomic analysis. 2-DE revealed that 52 protein spots exhibited statistically significantly changes among PCa and BPH groups. Interesting spots were identified by MALDI-TOF-MS/MS. The 2 most notable groups of proteins identified included latent androgen receptor coregulators [FLNA(7-15) and FKBP4] and enzymes involved in mitochondrial fatty acid beta-oxidation (DCI and ECHS1). An imbalance in the expression of peroxiredoxin subtypes was noted in PCa specimens. Furthermore, different post-translationally modified isoforms of HSP27 and HSP70.1 were identified. Importantly, changes in FLNA(7-15), FKBP4, and PRDX4 expression were confirmed by immunoblot analyses. Our results suggest that a proteomics-based approach is useful for developing a more complete picture of the protein profile of PNBX specimen. The proteins identified by this approach may be useful molecular targets for PCa diagnostics and therapeutics.

In vitro insulin refolding: Characterization of the intermediates and the putative folding pathway

The in vitro refolding process of the double-chain insulin was studied based on the investigation of in vitro single-chain insulin refolding. Six major folding intermediates, named P1A, P2B, P3A, P4B, P5B, and P6B, were captured during the folding process. The refolding experiments indicate that all of these intermediates are on-pathway. Based on these intermediates and the formation of hypothetic transients, we propose a two-stage folding pathway of insulin. (1) At the early stage of the folding process, the reduced A chain and B chain individually formed the intermediates: two A chain intermediates (P1A and P3A), and four B chain intermediates (P2B, P4B, P5B, and P6B). (2) In the subsequent folding process, transient I was formed from P3A through thiol/disulfide exchange reaction; then, transients II and III, each containing two native disulfides, were formed through the recognition and interaction of transient I with P4B or P6B and the thiol group's oxidation reaction mainly using GSSG as oxidative reagent; finally, transients II and III, through thiol/mixture disulfide exchange reaction, formed the third native disulfide of insulin to complete the folding.

Molecular and biochemical characterization of Ba-EGA, a cellulase secreted by Bacillus sp. AC-1 from Ampullaria crosseans

A novel gene (Ba-ega) of Bacillus sp. AC-1, encoding an endoglucanase (Ba-EGA), was cloned and expressed in Escherichia coli. Ba-ega, containing a 1,980-bp open reading frame (ORF), encoded a protein of 659 amino acids and had a molecular mass of 74.87 kDa. Ba-EGA was a modular enzyme composed of a family-9 glycosyl hydrolase catalytic module (CM9) and a family-3 carbohydrate-binding module (CBM3). To investigate the functions of the CBM3 and CM9, a number of truncated derivatives of Ba-EGA were constructed, and all were active. The catalytic module (rCM9) alone was less stable at high temperature than the recombinant Ba-EGA (rBa-EGA). The temperature stability for the complex of rCM9 and rCBM3 was still lower than rBa-EGA, but higher than rCM9 alone. These observations indicated the existence of a non-covalent interaction between CM9 and CBM3 that might strengthen the stability of CM9. However, this interaction is not strong enough to mimic the protective effect of the CBM in the wild-type enzyme.

The sequence determinant causing different folding behaviors of insulin and insulin-like growth factor-1

Although insulin and insulin-like growth factor-1 (IGF-1) belong to the insulin superfamily and share highly homologous sequences, similar tertiary structure, and a common ancestor molecule, amphioxus insulin-like peptide, they have different folding behaviors: IGF-1 folds into two thermodynamically stable tertiary structures (native and swap forms), while insulin folds into one unique stable structure. To further understand which part of the sequence determines their different folding behavior, based on previous reports from the laboratory, two peptide models, [B9A][1-4]porcine insulin precursor (PIP) and [B10E][1-4]PIP, were constructed. The plasmids encoding the peptides were transformed into yeast cells for expression of the peptides; the results showed that the former peptide was expressed as single component, while the latter was expressed as a mixture of two components (isomer 1 and isomer 2). The expression results together with studies of circular dichoism, disulfide rearrangement, and refolding lead us to deduce that isomer 1 corresponds to the swap form and the isomer 2 corresponds to the native form. We further demonstrate that the sequence 1-4 plus B9 of IGF-1 B-domain can make PIP fold into two structures, while sequence 1-5 of insulin B-chain can make IGF-1 fold into one unique structure. In other words, it is the IGF-1 B-domain sequence that 1-4 allows IGF-1 folding into two thermodynamically stable tertiary structures; this sequence plus its residue B9E can change PIP folding behavior from folding into one unique structure to two thermodynamically stable structures, like that of IGF-1.

Study on substrate specificity at subsites for severe acute respiratory syndrome coronavirus 3CL protease

Abstract Autocleavage assay and peptide‐based cleavage assay were used to study the substrate specificity of 3CL protease from the severe acute respiratory syndrome coronavirus. It was found that the recognition between the enzyme and its substrates involved many positions in the substrate, at least including residues from P4 to P2′. The deletion of either P4 or P2′ residue in the substrate would decrease its cleavage efficiency dramatically. In contrast to the previous suggestion that only small residues in substrate could be accommodated to the S1′ subsite, we have found that bulky residues such as Tyr and Trp were also acceptable. In addition, based on both peptide‐based assay and autocleavage assay, Ile at the P1′ position could not be hydrolyzed, but the mutant L27A could hydrolyze the Ile peptide fragment. It suggested that there was a stereo hindrance between the S1′ subsite and the side chain of Ile in the substrate. All 20 amino acids except Pro could be the residue at the P2′ position in the substrate, but the cleavage efficiencies were clearly different. The specificity information of the enzyme is helpful for potent anti‐virus inhibitor design and useful for other coronavirus studies.

Edited by Ming‐Hua XU

Purification and characterization of two endo-beta-1,4-glucanases from mollusca, Ampullaria crossean

Two novel endo-beta-1,4-glucanases, EG45 and EG27, were isolated from the gastric juice of mollusca, Ampullaria crossean, by anion exchange, hydrophobic interaction, gel filtration and a second round of anion exchange chromatography. The purified proteins EG45 and EG27 appeared as a single band on sodium dodecylsulfate polyacrylamide gel electrophoresis with a molecular mass of 45 kDa and 27 kDa, respectively. The optimum pH for CMC activity was 5.5 for EG45 and 4.4-4.8 for EG27. The optimum temperature range for EG27 was broad, between 50 degrees and 60 degrees; for EG45 it was 50 degrees. The analysis on the stability of these two endo-beta-1,4-glucanases showed that EG27 was acceptably stable at pH 3.0-11.0 even when the incubation time was prolonged to 24 h at 30 degrees, whereas EG45 remained relatively stable at pH 5.0-8.0. About 85% of the activity of EG27 could be retained upon incubation at 60 degrees for 24 h. However, less than 10% residual activity of EG45 was detected at 50 degrees. Among different kinds of substrates, both enzymes showed a high preference for carboxymethyl cellulose. EG45, in particular, showed a carboxymethyl cellulose hydrolytic activity of 146.5 IU/mg protein. Both enzymes showed low activities to xylan (from oat spelt) and Sigmacell 101, and they were inactive to p-nitrophenyl-beta-D-cellobioside, salicin and starch.

A novel thermoacidophilic endoglucanase, Ba-EGA, from a new cellulose-degrading bacterium, Bacillus sp.AC-1

A newly discovered bacterium, strain AC1, containing cellulase was isolated from the gastric juice of the mollusca, Ampullaria crosseans. Analysis of the 16S rDNA sequence and carbon sources revealed that the bacterium belonged to the genus Bacillus. A novel endoglucanase (Ba-EGA) was purified from culture supernatants of the bacterium growing in CMC-Na (low viscosity) induction medium. The cellulase was purified about 150-fold by ammonium sulfate fractionation, ion exchange, hydrophobic, and gel filtration chromatography, with a specific activity of 35.0 IU/mg. The molecular mass of the enzyme was 67 kDa. N-terminal amino acid sequencing revealed a sequence of SDYNYVEVLQKSILF, which had high homology with endoglucanases from the Bacillus and Clostridium species. The maximal activity of the enzyme with the substrate of CM-cellulose is at pH 4.5-6.5 and 70 degrees C, respectively. The studies on pH and temperature stability showed that the Ba-EGA is stable enough between pH 7.5 and 10.5 at 30 degrees C for 2 h, and more than 80% of the activity still remains when incubation was prolonged to 1 h at 50 degrees C. The activity of the enzyme was significantly inhibited by Fe(2+), Cu(2+) (5.0 mM of each), and sodium dodecyl sulfate (SDS) (0.5%) and obviously activated by Tween 20 and Triton X-100 (0.25% each). Binding studies revealed that the Ba-EGA had cellulose-binding domain.

Proteomic analysis of differential protein expression in a human hepatoma revertant cell line by using an improved two-dimensional electrophoresis procedure combined with matrix assisted laser desorption/ionization-time of flight-mass spectrometry

The proteomic profiles of a human hepatoma revertant, CL1, and its original cell line, SMMC7721, were compared by using an improved two-dimensional electrophoresis (2-DE) procedure, with multi-IPGstrips gels (length <or= 13 cm) run simultaneously on one sodium dodecyl sulfate (SDS) gel (shortened MSOG method). Nineteen proteins, showing significant difference in expression (P < 0.01), were selected and identified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and database search. In the revertant CL1 cells, compared to human hepatoma SMMC7721 cells, upregulated expression levels of some proteins related to tumor suppression, like maspin, were found, whereas some proteins related to tumor growth, like cathepsin D, were downregulated. These facts suggest that the phenotypic reversion of the CL1 cells was at least partially due to changes at the translational level of the proteins which favored the reconstruction of the normal phenotype of the cell.

A novel auto-cleavage assay for studying mutational effects on the active site of severe acute respiratory syndrome coronavirus 3C-like protease

The 3C-like protease (3CL^pro) of severe acute respiratory syndrome (SARS) has been proposed as an attractive target for drug design. His⁴¹ and Cys¹⁴⁵ were essential for the active site as the principal catalytic residues. In this study, we mutated the two sites, expressed four resulting mutants in Escherichia coli and characterized. All mutants showed undetectable activity in trans-cleavage assay. In addition, we introduced a 31-mer peptide containing an auto-cleavage site to the N-terminal of the proteases and found the peptide could be cleaved efficiently by 3CLsc itself, but, among the four mutants, only the mutant Cys¹⁴⁵ → Ser showed residual activity as detected by the auto-cleavage assay. The data supported the proposition unequivocally that SARS-CoV 3CL^pro was a member of serine proteases involving His⁴¹ and Cys¹⁴⁵ residues at the active site. The auto-cleavage assay also provided a sensitive and reliable compensation to the traditional trans-cleavage assay.

The role of propeptide in the refolding of human group IB phospholipase A2

Human group IB phospholipase A2 (IB-PLA2) and its zymogen (proIB-PLA2) were purified from E.coli. Refolding was carried out by diluting the denatured forms of both IB-PLA2 and proIB-PLA2 with renaturation buffer in which the disulfide bonds were completely reduced. The refolding yield of proIB-PLA2 was increased by about 50% over that of the mature enzyme. The refolding of IB-PLA2 usually produced aggregates under normal conditions, as determined by light scattering. In addition, the unfolding experiments showed that the mature enzyme was more stable than the proenzyme toward denaturants in the presence of DTT. Results suggested that the N-terminal sequence rather than its conformation of human proIB-PLA2 played an important role in the refolding process.

pH-dependent stability of EGX, a multi-functional cellulase from mollusca, Ampullaria crossean

The cellulase activity and stability of EGX, a multi-functional cellulase previously purified from the mollusca Ampullaria crossean, was systematically studied under different pH. The pH induced con-formation and stability change of EGX have been investigated by using the intrinsic fluorescence, ANS fluorescence and CD spectrum. It has been found that the conformation and activity of this cellulase were strongly dependent on the pH. EGX was stable for both the enzyme activity and the conformation from pH 5.6 to pH 7.4. As shown by intrinsic and ANS fluorescence, no red shift of emission maximum occurred and a negligible intensity change was observed at pH 5.6-7.4. The activity of EGX remained about 80% in pH 5.6-7.4 and obviously decreased out of side the pH range. Urea-induced changes in EGX at pH 5.4 and pH 8.0 were measured by intrinsic fluorescence and CD spectrum. At pH 5.4, a significantly red shift of emission maximum occurred when the concentration of urea was 5 M compared to the concentration was 3 M at pH 8.0. The alpha-helix at pH 5.4 was 40.51% in the absence of urea and 31.04% in the presence of 4 M urea. At pH 8.0 the alpha-helix was 7.23% in the presence of 4 M urea. The data indicated that EGX was much susceptible to urea-induced unfolding at pH 8.0 and much stable at pH 5.4. The greater pH dependent stability of EGX may allow the enzyme to adequately catalyze the hydrolysis of cellulosic materials under natural or industrial extreme conditions.

[A method for delineation of domains in proteins based on refolding free energy--application to continuous and discontinuous domains]

Domain is a protein architecture in a subunit. It might be defined as a basic unit for structure, function, folding, evolution and design. Different combinations of domains lead to the formation of various tertiary structures with various functions for proteins. The delineation of domains for a protein is important both conceptually and practically, which remains up to date a challenging and unsolved problem. Based on the above definition, a method was previously proposed based on refolding free energy to define continuous domains in proteins. By constructing a residue-residue contact matrix, using correspondence analysis, and then selecting optimal partition function of a protein according to refolding free energy and some empirical scoring functions, a new computer program, PDOM, was developed, which was applicable to both continuous and discontinuous domains. When compared with the manual partition results reported by crystallographers, PDOM has achieved an accuracy of 76% on a test data set including 55 protein structures frequently used. The differences in 13 proteins between PDOM, literature as well as SCOP have been discussed extensively.

Isolation of a multi-functional endogenous cellulase gene from mollusc, Ampullaria crossean

The cellulase genes of some animals, most coding for endo-beta-1,4-glucanases, were found and cloned. There has been no reports about genes encoding exo-beta-1,4-glucanase or endo- -1,4-xylanase from animal. Here we cloned the cDNA of a cellulase designated as EGX from mollusc, Ampullaria crossean, and expressed it in Pichia pastoris for the first time. The cellulase EGX is a multi-functional beta cellulase with the activities of exo-beta-1,4-glucanase, endo-beta-1,4-glucanase and endo-beta-1,4-xylanase. The opening reading frame of EGX cDNA is 1185 bp and encodes 395 amino acids. The EGX gene can also be amplificated from the genomic DNA by PCR, which verified the endogenous origin of this gene. This EGX gene was the first multi-functional cellulase gene that was directly isolated from animals.

A monovalent anion affected multi-functional cellulase EGX from the mollusca, Ampullaria crossean

A cellulose hydrolytic enzyme was isolated from the stomach juice of Ampullaria crossean, a kind of herbivorous mollusca. The enzyme was purified 45.3-fold to homogenety by ammonium sulfate precipitation, DEAE-Sephadex A-50 column, Bio-gel P-100 gel filtration column, and phenyl-Sepharose CL-4B column chromatography. The enzyme was designated as cellulase EGX. The purified enzyme is a multi-functional enzyme with the activities of exo-beta-1,4-glucanase (14.84 U/mg for p-nitrophenyl beta-D-cellobioside), endo-beta-1,4-glucanase (40.3 U/mg for carboxymethyl cellulose), and endo-beta-1,4-xylanase (196 U/mg for soluble xylan from birchwood). The monovalent anions such as F(-), Cl(-), Br(-), I(-), and NO(3)(-) are essential for its exo-beta-1,4-glucanase activity but have no effect on the activity for xylan, while I(-) higher than 5mM would inhibit the exo-beta-1,4-glucanase activity. The monovalent anions Cl(-) and Br(-) activate its endo-beta-1,4-glucanase activity. Binding of Cl(-) enhances the thermostability of EGX, but does not affect its fluorescence emission spectrum. The molecular mass of EGX is 41.5 kDa, as determined by SDS-PAGE. The pI value is about pH 7.35. The xylan hydrolytic activity of EGX reaches to the maximum between pH 4.8 and 6.0 and the pNPC hydrolytic activity reaches the maximum between pH 4.8 and 5.6, while that for CMC hydrolytic activity is between pH 4.4 and 4.8. Preliminary results showed that the enzyme was secreted by the mollusca itself.

Unfolding and inactivation of Ampullarium crossean beta-glucosidase during denaturation by guanidine hydrochloride

Changes of activity and conformation of Ampullarium crossean beta-glucosidase in different concentrations of guanidine hydrochloride (GuHCl) have been studied by measuring the fluorescence spectra and its relative activity after denaturation. The fluorescence intensity of the enzyme decreased distinctly with increasing guanidine concentrations, the emission peaks appeared red shifted (from 338.4 to 350.8 nm), whereas a new fluorescence emission peak appeared near 310 nm. Changes in the conformation and catalytic activity of the enzyme were compared. A corresponding rapid decrease in catalytic activity of the enzyme was also observed. The extent of inactivation was greater than that of conformational changes, indicating that the active site of the enzyme is more flexible than the whole enzyme molecule. k(+0)>k(+0)' also showed that the enzyme was protected by substrate to a certain extent during guanidine denaturation.

Fluorescence Red-edge-excitation Effects of Human Serum Albumin

We have studied the fluorescence red-edge-excitation effects of human serum albumin. Our results indicate that the red-edge-excitation effects of human serum albumin depend on the pH, temperature and concentration of the denaturant. The different red-edge-excitation effects are produced by a redistribution of the energy levels both in the ground and the exited states of the chromphore aroused by changes of external conditions. Studying red-edge-excitation effects of HAS, we have observed that under of acidic pH and high temperature the two denatured states of HAS have different conformations, and at pH 7.4 with increasing temperature there was a conformation transition process similar to that of acid denaturation.

Purification and Kinetic Studies of Yeast Alcohol Dehydrogenase I

An efficient procedure for the purification of yeast alcohol dehydrogenase I (ADHI) was developed. By using Blue-Sepharose 4B affinity chromatography, ADHI from yeast (S. cerevisiae) was purified 200-fold with an overall yield of 47% to homogeneity as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis and starch gel electrophoresis. Results of studies on the product and dead-end inhibition kinetics were in agreement with and ordered Bi Bi mechanism as proposed by Wratten and Cleland. Dioxane was found to be a competitive inhibitor of this enzyme. The complexity of the reaction mechanism of this enzyme is discussed.

The Preparation of the Antigen Conformation-related Monoclonal Antibodies against Maltose-Binding Protein

Making use of the high expression efficiency of maltose-binding protein (MBP) in E. coli, the soluble and the inclusion body forms of MBP were purified to homogeneity by affinity chromatography and by denaturation, refolding and gel filtration respectively. After immunized Balb/C mice with two forms of MBP respectively, 5 clones for each antigen form were found to secrete monoclonal antibodies. The binding experiments showed that two antibodies obtained by the immunization with the refolded form of MBP had high affinity to the denatured MBP.

Snake Muscle Creatine Kinase cDNA Molecular Cloning, Expression and Comparison with Evolutionarily Related Enzymes

Snake muscle cDNA library was constructed, and an allelic cDNA coding for M-type creatine kinase was cloned through screening library with antibody. A complete open reading frame(1 140 bp) codes for 380 amino acids which shows high homology with known creatine kinase isoenzyme. After cloning into expression vector pET11a, the snake muscle creatine kinase(SM-CK) was over-expressed in Escherchia coli. Kinetical studies showed that purified recombinant SM-CK exhibited behavior similar to the tissue form. Evolutionary tree of M-type creatine kinase was then constructed, and it was determined that this allelic cDNA of snake muscle creatine kinase belonged to M-type situated between in mammals and birds. These findings, along with the following SM-CK gene regulation studies, may shed light on the role of creatine kinase in energy generation during hibernation as well as the molecular basis of myogenesis during ontogeny.

Delineation of Continuous Domains in Proteins by Differences of Free Energy

Domain is a protein architecture under proteins' tertiary structure,which can be identified in most of proteins. Different combinations of domains lead to the formation of diverse tertiary structures with diverse function for proteins. The delineation of domains for a protein is important not only conceptually but also practically. Unfortunately, up to now there is not an ideal means to achieve that. This paper proposes a method for domain delineation based on the maximum refolding free energy. The criteria are more or less objective. By using this method, 50 proteins are analyzed. The boundaries for most proteins agree with the data reported in literature. There are a few examples that seem more reasonable, although they are not identical with those in literature.

Structural and redox properties of the leaderless DsbE (CcmG) protein: both active-site cysteines of the reduced form are involved in its function in the Escherichia coli periplasm

The thiol/disulfide oxidoreductases play important roles in ensuring the correct formation of disulfide bonds, of which the DsbE protein, also called CcmG, is the one implicated in electron transfer for cytochrome c maturation in the periplasm of Escherichia coli. The soluble, N-terminally truncated DsbE was overexpressed and purified to homogeneity. Here we report the structural and redox properties of the leaderless form (DsbEL-). During the redox reaction, the protein undergoes a structural transformation resulting in a more stable reduced form, but this form shows very low reactivity in thiol/ disulfide exchange of cysteine residues and low activity in accelerating the reduction of insulin. The standard redox potential (E'0) for the active thiol/ disulfide was determined to be -0.186 V; only one of the two cysteines (Cys80) was suggested to be the active residue in the redox reaction. From the aspect of biochemical properties, DsbE can be regarded as a weak reductant in the Escherichia coli periplasm. This implies that the function of DsbE in cytochrome c maturation can be ascribed to its active-site cysteines and the structure of the reduced form.

Crystallization and preliminary crystallographic data of fructose-1,6-bisphosphatase from human muscle

The enzyme human muscle fructose-1,6-bisphosphatase, which plays a critical role in gluconeogenesis, has been crystallized in the presence of 2-propanol, polyethylene glycol and magnesium chloride at pH 7.5. The space group was determined to be P4(2)2(1)2, with unit-cell parameters a = b = 73.57, c = 146.50 A, alpha = beta = lambda = 90 degrees and one subunit in the asymmetric unit. A 99.6% complete data set to 2.04 A has been collected at the National Synchrotron Light Source.

Probing local conformational changes during equilibrium unfolding of firefly luciferase: fluorescence and circular dichroism studies of single tryptophan mutants

Firefly luciferase is a monomeric protein composed of two globular domains. There is a wide cleft between the two domains. The N-terminal domain can be further divided into A-, B-, and C-subdomains. Previous studies showed that in vitro unfolding of firefly luciferase induced by guanidinium chloride can be described as a four-state equilibrium with two inactive intermediates (Herbst, R., et al. (1997) J. Biol. Chem. 272, 7099-7105). In order to monitor spectroscopically the conformational changes that occur in the different domains and subdomains during the multi-state unfolding process, we constructed a series of single-tryptophan mutants. These mutants were purified and characterized and shown to retain essentially all of the structural properties of the wild-type luciferase. Under equilibrium conditions, the unfolding of each mutant protein were studied by means of fluorescence and circular dichroism. The results show that different conformational changes occur in specific regions, suggesting a sequential unfolding process for firefly luciferase. Under 2.5 M GdmCl, whereas the N-domain unfolds partially holding half of the secondary structure content, the C-domain unfolds almost completely. In the equilibrium intermediate I(2), the secondary structure might stem mostly from the A- and B- subdomains.

Association and activation of fructose 1,6-bisphosphase during unfolding and refolding: spectroscopic and enzymatic studies

Fructose 1,6-biphosphase is a well-characterized oligomer enzyme, and many effectors allosterically control its activity. In this report, we compared the activity, allosteric properties, and conformational changes in its denaturant-induced unfolding processes. In addition, a trpytophan residue has been introduced into the interface between the C1 and C2 subunits to investigate conformational changes during unfolding. Results show that the denaturation curves of WT FruP2ase detected by various methods do not agree, and the dissociation occurs first with a monomeric form existing around 0.4 M GdmCl as shown by gel filtration. The dissociation of all mutants is accompanied by changes in fluorescence intensity. The results suggest that the unfolding of FruP2ase is a complicated, multiphase process. The activation of FruP2ase by GdmCl at low concentrations can be interpreted as a consequence of the effect of monovalent cation. In the refolding experiments, it is found that Mg2+ is not only essential for enzyme activity, but also can assist the enzyme in refolding and association by preventing the formation of aggregates.

Magnet used for protein crystallization: novel attempts to improve the crystal quality

The accuracy of the structures of biological macromolecules determined by X-ray crystallography is of fundamental importance, both for the understanding of life processes and for medical applications. The resolution of the structure is thus critical, and is largely determined by the quality of single crystals. Here we report the results of applying a magnetic field and a magnetization force during growth of the snake muscle fructose-1,6-bisphosphatase and human estrogenic 17beta-hydroxysteroid dehydrogenase crystals. For both enzyme proteins, the quality of the crystals improved with repeated assay, and their data sets were collected at significantly higher resolutions. These results coincide with a mechanism involving the reduction of convection, due to both the hydrodynamics within a magnet and the partially reduced gravity induced by a magnetization force. The density difference between the crystal and solution becomes less significant, and the sedimentation speed of the crystals is also reduced in the presence of the magnetization force.

Molecular cloning, expression and purification of muscle fructose-1,6-bisphosphatase from Zaocys dhumnades: the role of the N-terminal sequence in AMP activation at alkaline pH

An open reading frame (ORF) of snake muscle fructose-1,6-bisphosphatase (Fru-1,6-P2ase) was obtained by the RT-PCR method with degenerate primers, followed by RACE-PCR. The cDNA of Fru-1,6-P2ase, encoding 340 amino acids, is highly homologous to that of mammalian species, especially human muscle, with a few exceptions. Kinetic parameters of the purified recombinant enzyme, including inhibition behavior by AMP, were identical to that of the tissue form. Replacement of the N-terminal sequence of this enzyme by the corresponding region of rat liver Fru-1,6-P2ase shows that the activity was fully retained in the chimeric enzyme. The inhibition constant (Ki) of AMP at pH 7.5, however, increases sharply from 0.85 microM (wild-type) to 1.2 mM (chimeric enzyme). AMP binding is mainly located in the N-terminal region, and the allosteric inhibition was shown not to be merely determined by the backbone of this region. The fact that the chimeric enzyme could be activated at alkaline pH by AMP indicated that the AMP activation requires the global structure beyond the area.

Study of the redox properties of metallothionein in vitro by reacting with DsbA protein

Mammalian metallothionein (MT) contains 20 cysteine residues involved in the two metal clusters without a disulfide bond. The redox reaction of the Cys thiols was proposed to be associated with the metal distribution of MT. The E. coli DsbA protein is extremely active in facilitating thiol/disulfide exchange both in vivo and in vitro. To further investigate the redox properties of MT, reaction between MT and DsbA was carried out in vitro by fluorescence detection. Equilibrium characterization indicates that the reaction is stoichiometric (1:1) under certain conditions. Kinetic study gives a rate constant of the redox reaction of 4.42 x 10(5) sec(-1) M(-1), which is 10(3)-fold larger than that of glutathione reacting with DsbA. Metal-free MT (apo-MT) shows a higher equilibrium reduction potential than MT, but exhibits an indistinguishable kinetic rate. Oxidation of MT by DsbA leads to metal release from the clusters. The characteristic fluorescence increase during reduction of DsbA may provide a sensitive probe for exploring the redox properties of some reductants of biological interest. The result also implies that oxidation of Cys thiols may influence the metal release or delivery from MT.

Crystallization and preliminary crystallographic analysis of the snake muscle fructose 1,6-bisphosphatase

The snake muscle fructose 1,6-bisphosphatase, a typical allosteric enzyme which plays important roles in gluconeogenesis, was crystallized in the presence of polyethylene glycol 3350 and magnesium chloride at pH 8.5. The crystals diffract to 2.3 A on a rotating-anode X-ray source. The space group was determined to be either P3121 or its enantiomorph P3221, with unit-cell parameters a = b = 83.7, c = 202.41 A, alpha = beta = 90 and gamma = 120 degrees. There are two subunits in the asymmetric unit. Preliminary molecular-replacement studies indicate that the first enantiomorph is the correct one.

A sesquiterpene lactone glucoside from Ixeris denticulata f. pinnatipartita

An extract from the entire Ixeris denticulata f. pinnatipartita plant afforded the guaianolide sesquiterpene lactone glucoside, 8 beta,15-dihydroxy-1(10),3,11(13)-guaiatrien-12,6-olide-15-O- glucopyranoside, along with the known flavonoids luteolin-7-O-glucoside and luteolin-7-O-glucuronide-6'-methyl ester; their structures were determined by spectroscopic methods. Ixerin Y inhibited the growth of human breast cancer MCF7 and MDA468 cell lines.

AMP activation of snake muscle fructose 1,6-bisphosphatase at alkaline pH

AMP, an allosteric inhibitor at neutral pH, activates snakes muscle fructose 1,6-bisphosphatase at pH 9.2. The activation is virtually unique for the snake muscle enzyme: activation was not observed for the enzymes from either human and rabbit liver or porcine kidney. The activation is Mg(2+)-dependent but was not observed until the concentration of Mg2+ reaches 1 mM. It is known that subtilisin, trypsin, or lysosomal proteases hydrolyse the N-terminal loop of fructose-1,6-bisphosphatase in the vicinity of amino acid residue 60 generating a form of the enzyme with a pH optimum at 9.2. In the presence of AMP, the pH profile of the native snake muscle enzyme resembles that of the alkaline form and modification of the highly reactive sulfhydryl group abolishes AMP activation. The fact that AMP has a dual function at different pH levels suggests that pH might be an important factor in regulating the activity of the enzyme upon binding of AMP at the allosteric site. Indeed, the mode of AMP binding to the allosteric site may differ at neutral and alkaline pH levels. A residue that ionizes with a pKa of 8.9 might be involved in this process.

Substrate induced reactivation of spinach ribulose-1,5-bisphosphate carboxylase/oxygenase denatured by low concentrations of guanidine hydrochloride

The unfolding and refolding behavior of the hexadecameric ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from spinach in solutions of guanidine hydrochloride (GdnHCl) was studied. By a number of criteria (enzyme activity, protein fluorescence, circular dichroism), the enzyme was judged to be almost completely unfolded in 6 M GdnHCl. The changes in enzyme activity occur at lower concentrations of GdnHCl than those required to bring about changes in circular dichroism (CD) and fluorescence, as has been found for other enzymes. Spinach Rubisco is completely inactive in 0.5 M GdnHCl with no apparent changes observed in the overall structure of the enzyme as monitored by CD and intrinsic fluorescence. The result of the size-exclusion chromatography indicates that the inactive enzyme still exists in the hexadecameric state. On dilution of the GdnHCl, reactivation of the inactive enzyme by low concentrations of GdnHCl occurred. The regain of activity was time-dependent and obeyed first-order kinetics, and the substrate, ribulose-1,5-biphosphate, can stimulate this reactivation process. The result suggests that the inactivation of the Rubisco in dilute GdnHCl is caused by the conformational changes at the active site instead of the inhibition of guanidine hydrochloride or the dissociation of the oligomeric enzyme molecules.

Inactivation kinetics of the reduced spinach chloroplast fructose-1,6-bisphosphatase by subtilisin

The course of inactivation of the reduced spinach chloroplast fructose-1,6-bisphosphatase by digestion with subtilisin has been followed by the progress curve method [Tsou, C. L. (1988) Adv. Enzymol. 61, 381-436] and found to follow first-order kinetics. On the basis of the hydrolysis of the substrate, fructose 1,6-bisphosphate, at different concentrations during proteolysis by subtilisin, the first-order inactivation rate constants for the free enzyme and the enzyme-substrate complex can both be determined. The ratio between the inactivation rate constants for the free enzyme and the enzyme-substrate complex indicates strong protection against subtilisin proteolysis by the substrate. It is proposed that the above ratio can be used as a quantitative measure of substrate protection for enzyme inactivation generally. As it has been found that the site of proteolysis is located in a loop region near the N-terminus and well away from the active site, the substrate protection indicates a conformation change of the enzyme away from the substrate binding site.

Investigations on the protective action of Condonopsis pilosula (Dangshen) extract on experimentally-induced gastric ulcer in rats

The action of Codonopsis pilosula extract in 5 animal models of gastric ulcer was investigated. It was found that the extract had higher efficacy on gastric ulcer induced by stress, acetic acid and sodium hydroxide and little significant effect on ulcers induced by pyloroligature and indomethacin. The C. pilosula extract was also capable of reducing gastric acid pepsin secretion. It is possible that inhibition of gastrointestinal movement and propulsion is one of the mechanisms underlying the antiulcer action of C. pilosula extract.

Immunomodulatory effect of a polysaccharide-enriched preparation of Codonopsis pilosula roots

1. A polysaccharide-enriched fraction (CPPS) was prepared from Codonopsis pilosula root extract utilizing a procedure that entailed extraction with aqueous buffer and precipitation with ethanol. 2. After administration of CPPS in drinking water to C57BL/6 mice at a dosage of 10 mg/L for 4 weeks, the splenocytes exhibited lowered mitogenic responses to Concanavalin A (ConA) and lipopolysaccharide (LPS). The in vitro production of reactive nitrogen intermediates was inhibited. 3. However, when oral administration of CPPS was prolonged to 8 weeks, there was a potentiation of ConA-stimulated and LPS-stimulated mitogenic responses. 4. When tested under in vitro conditions, CPPS augmented the mitogenic response of splenocytes to ConA. However, there was no effect on the pinocytic activity of mouse macrophages, nor was there any proliferative activity on mouse melanoma B16 cells.

Examination of coumarins, flavonoids and polysaccharopeptide for antibacterial activity

1. Coumarins, flavonoids and polysaccharopeptide were tested for antibacterial activity. 2. The bacteria used for this study included clinical isolates of Staphylococcus aureus, Shigella flexneri, Salmonella typhi, Escherichia coli and Pseudomonas aeruginosa. 3. Most of the coumarins tested failed to inhibit the bacteria at 25 mg/l. Edultin at 128 mg/l inhibited 4 of the 8 P. aeruginosa strains and 1 of the S. aureus strains tested. O-acetylcolumbianetin and imperatorin did not inhibit any isolate, even at 128 mg/l. 4. When tested at the dose of 128 mg/l, the flavonoids (rutin, naringin and baicalin) inhibited 25% or less of P. aeruginosa and only baicalin was active against S. aureus. 5. Arbutin and 4-(beta-D-glucopyranosyloxyl)-benzaldehyde inhibited 3 of the 8 P. aeruginosa strains when tested at 128 mg/l. 6. Polysaccharopeptide from the fungus Coriolus versicolor failed to inhibit any P. aeruginosa or S. aureus strain at 128 mg/l.

Steroidal glycosides from the subterranean parts of Liriope spicata var. prolifera

In a continuation of phytochemical studies on the underground organs of Liriope spicata var. prolifera, four new steroidal glycosides, lirioproliosides A-D, along with two known compounds, 25(S)-ruscogenin 1-O-[alpha-L-rhamnopyranosyl(1-->2)[beta-D-xylopyranosyl (1-->3)]-beta-D-fucopyranoside and ophiopogonin A, were identified. The structures of lirioproliosides A-D were established by a combination of spectroscopic and chemical methods as 25(S)-ruscogenin 1-O-[alpha-L-rhamnopyranosyl(1-->2)][beta-D-xylopyranosyl (1-->3)]-beta-D-fucopyranoside-3-O-alpha-L-rhamnopyranoside, 25(S)-ruscogenin 1-O-[3-O-acetyl-alpha-L-rhamnopyranosyl(1-->2)]-beta-D-fucopyranoside, 25(S)-ruscogenin (1-O-[2-O-acetyl-alpha-L-rhamnopyranosyl (1-->2)]-beta-D-fucopyranoside and ruscogenin (1-O-[2-O-acetyl-alpha-L-rhamnopyranosyl(1-->2)]-beta-D-fucopyranoside, respectively. Among these steroidal glycosides, ophiopogonin A and lirioprolioside B, and lirioproliosides C and D, were isolated as epimeric pairs.

Redox modifications of spinach chloroplast fructose-1, 6-bisphosphatase

Complete activation of chloroplast fructose-1, 6-bisphosphatase by dithiothreitol involves the reduction of its four disulfide bonds as revealed by thiol titration and activity measurement. Both before and after reduction, the enzyme is inhibited by the thiol-specific reagent 5,5'-dithiobis(2-nitro-benzoic acid) with complete inactivation upon modifications of the four accessible thiols. However, oxidative modification of the enzyme facillitates the reduction of the four mentioned disulfide bonds as the process of activation by DTT is accelerated.