New complexes containing the internal alternative NADH dehydrogenase (Ndi1) in mitochondria of Saccharomyces cerevisiae

Mitochondria of Saccharomyces cerevisiae lack the respiratory complex I, but contain three rotenone-insensitive NADH dehydrogenases distributed on both the external (Nde1 and Nde2) and internal (Ndi1) surfaces of the inner mitochondrial membrane. These enzymes catalyse the transfer of electrons from NADH to ubiquinone without the translocation of protons across the membrane. Due to the high resolution of the Blue Native PAGE (BN-PAGE) technique combined with digitonin solubilization, several bands with NADH dehydrogenase activity were observed on the gel. The use of specific S. cerevisiae single and double mutants of the external alternative elements (ΔNDE1, ΔNDE2, ΔNDE1/ΔNDE2) showed that the high and low molecular weight complexes contained the Ndi1. Some of the Ndi1 associations took place with complexes III and IV, suggesting the formation of respirasome-like structures. Complex II interacted with other proteins to form a high molecular weight supercomplex with a molecular mass around 600 kDa. We also found that the majority of the Ndi1 was in a dimeric form, which is in agreement with the recently reported three-dimensional structure of the protein.

Toxins from Physalia physalis (Cnidaria) raise the intracellular Ca(2+) of beta-cells and promote insulin secretion

Physalia physalis is a marine cnidarian from which high molecular weight toxins with hemolytic and neurotoxic effects have been isolated. In the present work, two novel toxins, PpV9.4 and PpV19.3 were purified from P. physalis by bioactive guideline isolation. It involved two steps of column chromatography, gel filtration and RP-HPLC. The molecular weights were 550.7 and 4720.9 Da for PpV9.4 and PpV19.3, respectively. In the light of the Edman sequencing results, the structure of these toxins included the presence of modified amino acids. Both toxins increased the percentage of insulin secreting beta-cells and induced cytosolic Ca2+ elevation. To date, this is the first report of low molecular weight toxins increasing insulin secretion purified from cnidarians, by constituting a new approach to the study of beta-cells physiology.

Water stress induces up-regulation of DOF1 and MIF1 transcription factors and down-regulation of proteins involved in secondary metabolism in amaranth roots (Amaranthus hypochondriacus L.)

Roots are the primary sites of water stress perception in plants. The aim of this work was to study differential expression of proteins and transcripts in amaranth roots (Amaranthus hypochondriacus L.) when the plants were grown under drought stress. Changes in protein abundance within the roots were examined using two-dimensional electrophoresis and LC/ESI-MS/MS, and the differential expression of transcripts was evaluated with suppression subtractive hybridisation (SSH). Induction of drought stress decreased relative water content in leaves and increased solutes such as proline and total soluble sugars in roots. Differentially expressed proteins such as SOD(Cu-Zn) , heat shock proteins, signalling-related and glycine-rich proteins were identified. Up-regulated transcripts were those related to defence, stress, signalling (Ser, Tyr-kinases and phosphatases) and water transport (aquaporins and nodulins). More noteworthy was identification of the transcription factors DOF1, which has been related to several plant-specific biological processes, and MIF1, whose constitutive expression has been related to root growth reduction and dwarfism. The down-regulated genes/proteins identified were related to cell differentiation (WOX5A) and secondary metabolism (caffeic acid O-methyltransferase, isoflavone reductase-like protein and two different S-adenosylmethionine synthetases). Amaranth root response to drought stress appears to involve a coordinated response of osmolyte accumulation, up-regulation of proteins that control damage from reactive oxygen species, up-regulation of a family of heat shock proteins that stabilise other proteins and up-regulation of transcription factors related to plant growth control.

Increased synthesis of α-tocopherol, paramylon and tyrosine by Euglena gracilis under conditions of high biomass production

AIMS

To analyse the production of different metabolites by dark-grown Euglena gracilis under conditions found to render high cell growth.

METHODS AND RESULTS

  The combination of glutamate (5 g l(-1) ), malate (2 g l(-1) ) and ethanol (10 ml l(-1) ) (GM + EtOH); glutamate (7·15 g l(-1) ) and ethanol (10 ml l(-1) ); or malate (8·16 g l(-1) ), glucose (10·6 g l(-1) ) and NH(4) Cl (1·8 g l(-1) ) as carbon and nitrogen sources, promoted an increase of 5·6, 3·7 and 2·6-fold, respectively, in biomass concentration in comparison with glutamate and malate (GM). In turn, the production of α-tocopherol after 120 h identified by LC-MS was 3·7 ± 0·2, 2·4 ± 0·1 and 2 ± 0·1 mg [g dry weight (DW)](-1) , respectively, while in the control medium (GM) it was 0·72 ± 0·1 mg (g DW)(-1) . For paramylon synthesis, the addition of EtOH or glucose induced a higher production. Amino acids were assayed by RP-HPLC; Tyr a tocopherol precursor and Ala an amino acid with antioxidant activity were the amino acids synthesized at higher concentration.

CONCLUSIONS

Dark-grown E. gracilis Z is a suitable source for the generation of the biotechnologically relevant metabolites tyrosine, α-tocopherol and paramylon.

SIGNIFICANCE AND IMPACT OF THE STUDY

By combining different carbon and nitrogen sources and inducing a tolerable stress to the cell by adding ethanol, it was possible to increase the production of biomass, paramylon, α-tocopherol and some amino acids. The concentrations of α-tocopherol achieved in this study are higher than others reported previously for Euglena, plant and algal systems. This work helps to understand the effect of different carbon sources on the synthesis of bio-molecules by E. gracilis and can be used as a basis for future works to improve the production of different metabolites of biotechnological importance by this organism.

The succinate:menaquinone reductase of Bacillus cereus: characterization of the membrane-bound and purified enzyme

Utilization of external succinate by Bacillus cereus and the properties of the purified succinate:menaquinone-7 reductase (SQR) were studied. Bacillus cereus cells showed a poor ability for the uptake of and respiratory utilization of exogenous succinate, thus suggesting that B. cereus lacks a specific succinate uptake system. Indeed, the genes coding for a succinate-fumarate transport system were missing from the genome database of B. cereus. Kinetic studies of membranes indicated that the reduction of menaquinone-7 is the rate-limiting step in succinate respiration. In accordance with its molecular characteristics, the purified SQR of B. cereus belongs to the type-B group of SQR enzymes, consisting of a 65-kDa flavoprotein (SdhA), a 29-kDa iron-sulphur protein (SdhB), and a 19-kDa subunit containing 2 b-type cytochromes (SdhC). In agreement with this, we could identify the 4 conserved histidines in the SdhC subunit predicted by the B. cereus genome database. Succinate reduced half of the cytochrome b content. Redox titrations of SQR-cytochrome b-557 detected 2 components with apparent midpoint potential values at pH 7.6 of 79 and -68 mV, respectively; the components were not spectrally distinguishable by their maximal absorption bands as those of Bacillus subtilis. The physiological properties and genome database analyses of B. cereus are consistent with the cereus group ancestor being an opportunistic pathogen.

Crystallization and identification of the glycosylated moieties of two isoforms of the main allergen Hev b 2 and preliminary X-ray analysis of two polymorphs of isoform II

Latex from Hevea brasiliensis contains several allergenic proteins that are involved in type I allergy. One of them is Hev b 2, which is a beta-1,3-glucanase enzyme that exists in different isoforms with variable glycosylation content. Two glucanase isoforms were isolated from trees of the GV-42 clone by gel filtration, affinity and ion-exchange chromatography. Isoform I had a carbohydrate content of about 20%, with N-linked N-acetyl-glucosamine, N-acetyl-galactosamine, fucose and galactose residues as the main sugars, while isoform II showed 6% carbohydrate content consisting of N-acetyl-glucosamine, fucose, mannose and xylose. Both isoforms were crystallized by the hanging-drop vapour-diffusion method. Isoform I crystals were grown using 0.2 M trisodium citrate dihydrate, 0.1 M Na HEPES pH 7.5 and 20%(v/v) 2-propanol, but these crystals were not appropriate for data collection. Isoform II crystals were obtained under two conditions and X-ray diffraction data were collected from both. In the first condition (0.2 M trisodium citrate, 0.1 M sodium cacodylate pH 6.5, 30% 2-propanol), crystals belonging to the tetragonal space group P4(1) with unit-cell parameters a = b = 150.17, c = 77.41 A were obtained. In the second condition [0.2 M ammonium acetate, 0.1 M trisodium citrate dihydrate pH 5.6, 30%(w/v) polyethylene glycol 4000] the isoform II crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 85.08, b = 89.67, c = 101.80 A, beta = 113.6 degrees. Preliminary analysis suggests that there are four molecules of isoform II in both asymmetric units.

Purification of Taenia solium cysticerci superoxide dismutase and myoglobin copurification

Superoxide dismutase from Taenia solium cysticerci ( Ts SOD) was purified by sequential ion exchange chromatography on quaternary-amino-ethyl-cellulose (QAE) followed by hydrophobic interaction on phenyl sepharose (PS) and chromatofocusing on a polybuffer exchanger 94 (PBE). Ts SOD is a 30 kDa molecular weight dimeric enzyme with 15 kDa monomers. It is partially negative, hydrophilic, with 6.3 isoelectric point and has 2,900 U/mg activity. Bovine erythrocyte SOD antibodies cross react with Ts SOD. This enzyme is 80% inhibited by 10 mM of KCN suggesting that it has a Cu/Zn active site. Furthermore, Ts SOD totally loses its activity at 100 degrees C for 4 min. The first 25 amino acids from the Ts SOD N-terminal are (M K A V X V M R G E E G V K G V V H F T Q A G D A). This sequence is 76% similar to the Schistosoma mansoni Cu/Zn SOD. By chance, myoglobin (Mb) was also found during the purification process. A 16 kDa band was recognized in immunoblotting by horse heart Mb antibodies in QAE, PS and PBE, the last-mentioned being found at pH 7.0. The first 15 amino acids from the amino terminal group (G L S D G E W Q L V L N V W G) in this 16 kDa protein are identical to several other Mbs which have been reported.

Characterization of a recombinant mu-class glutathione S-transferase from Taenia solium

A Taenia solium larval glutathione S-transferase fraction (SGSTF), composed of two proteins with Mr 25,500 (SGSTM1) and 26,500 (SGSTM2), was purified by GSH-sepharose. Its N-terminal sequence analysis revealed that both proteins are related to mammalian mu-class GST enzymes. A cDNA clone coding for SGSTM1 was isolated and the amino acid sequence analysis showed close identity with two Echinococcus GSTs and also high identity with several mu-class GSTs that have been reported. In addition, SGSTM1 presents a similar structure to mu-class GSTs, including the mu loop. The recombinant SGSTM1 is a dimeric protein with enzymatic properties clearly related to mammalian mu-class GSTs. Western blot studies indicated that SGSTM1 is not antigenically related to SGSTM2 or mammalian GSTs from rabbit, pig and rat livers. Immunization with SGSTF and SGSTM2 was highly effective in reducing cysticerci load in murine cysticercosis. In contrast, no protection was obtained using native SGSTM1 and recombinant SGSTM1 as immunogens.

Exocytosis of a 60 kDa protein (calreticulin) from activated hamster oocytes

The sp50 protein localized at the acrosomal region of guinea pig sperm was suggested to participate in acrosome exocytosis, the acrosome reaction (AR). On the other hand, the cortical reaction (CR), also an exocytotic event, occurs during egg activation. The aim of the present work was to identify sp50 and also to define if sp50 is present in hamster eggs, as well as its location before and after CR. Sp50 was identified as calreticulin (CRT), based on: (a) its NH(2)-terminal amino acid (25 aa) sequence, (b) a cross-recognition of pure sp50 and pure CRT with anti-CRT (from Santa Cruz, anti-CRTsc), and anti-sp50 (anti-sp50/CRT) antibodies, respectively, and (c) that both antibodies revealed a 50 kDa protein in a Brij sperm extract. On the other hand, CRT presence in eggs was positively determined by Western blotting (Wb) using anti-sp50/CRT antibody which recognized a 60 kDa protein in the egg extract, and by indirect immunofluorescence (IIF), CRT was located in the cortical granules (CG). It was defined by a granular pattern and co-localization with mannose, a specific carbohydrate of the CG. Additionally, a decrease in CRT concentration occurred in eggs after their activation and, in parallel, the protein was revealed in the egg's incubation medium. In activated eggs with zona pellucida (ZP), CRT remains as a halo in the perivitelline space and around the polar body. From these results we suggest that: (1) CRT is present in the CG of non-activated hamster eggs, (2) CRT is exocytosed during the CR, in response to egg activation, and (3) CRT might participate in the block to polyspermy, together with other CG components.

Unfolding kinetics of glutathione reductase from cyanobacterium Spirulina maxima

The kinetics of the irreversible unfolding of glutathione reductase (NAD[P]H:GSSG oxidoreductase, EC 1.6.4.2.) from cyanobacterium Spirulina maxima was studied at pH 7.0 and room temperature. Denaturation was induced by guanidinium chloride and the changes in enzyme activity, aggregation state, and tertiary structure were monitored. No full reactivation of enzyme was obtained, even after very short incubation times in the presence of denaturant. Reactivation plots were complex, showing biphasic kinetics. A very fast early event in the denaturation pathway was the dissociation of tetrameric protein into reactivatable native-like dimers, followed by its conversion into a nonreactivatable intermediary, also dimeric. In the final step of the unfolding pathway the latter was dissociated into denatured monomers. Fluorescence measurements revealed that denaturation of S. maxima glutathione reductase is a slow process. Release of the prostethic group FAD was previous to the unfolding of the enzyme. No aggregated species were detected in the unfolding pathway, dismissing the aggregation of denatured polypeptide chains as the origin of irreversibility. Instead, the transition between the two dimeric intermediates is proposed as the cause of irreversibility in the denaturation of S. maxima glutathione reductase. A value of 106.6 +/- 3 kJ mol(-1) was obtained for the activation free energy of unfolding in the absence of denaturant. No evidence for the native monomer in the unfolding pathway was obtained which suggests that the dimeric nature of glutathione reductase is essential for the maintenance of the native subunit conformation.

Recombinant soluble betaglycan is a potent and isoform-selective transforming growth factor-beta neutralizing agent

Betaglycan is an accessory receptor of members of the transforming growth factor-beta (TGF-beta) superfamily, which regulates their actions through ligand-dependent interactions with type II receptors. A natural soluble form of betaglycan is found in serum and extracellular matrices. Soluble betaglycan, prepared as a recombinant protein using the baculoviral expression system, inhibits the actions of TGF-beta. Because of its potential use as an anti-TGF-beta therapeutic agent, we have purified and characterized baculoviral recombinant soluble betaglycan. Baculoviral soluble betaglycan is a homodimer formed by two 110 kDa monomers associated by non-covalent interactions. This protein is devoid of glycosaminoglycan chains, although it contains the serine residues, which, in vertebrate cells, are modified by these carbohydrates. On the other hand, mannose-rich carbohydrates account for approximately 20 kDa of the mass of the monomer. End-terminal sequence analysis of the soluble betaglycan showed that Gly(24) is the first residue of the mature protein. Similarly to the natural soluble betaglycan, baculoviral soluble betaglycan has an equilibrium dissociation constant (K(d)) of 3.5 nM for TGF-beta1. Ligand competition assays indicate that the relative affinities of recombinant soluble betaglycan for the TGF-beta isoforms are TGF-beta2>TGF-beta3>TGF-beta1. The anti-TGF-beta potency of recombinant soluble betaglycan in vitro is 10-fold higher for TGF-beta2 than for TGF-beta1. Compared with a commercial pan-specific anti-TGF-beta neutralizing antibody, recombinant soluble betaglycan is more potent against TGF-beta2 and similar against TGF-beta1. These results indicate that baculoviral soluble betaglycan has the biochemical and functional properties that would make it a suitable agent for the treatment of the diseases in which excess TGF-beta plays a central physiopathological role.

Pet toxin from enteroaggregative Escherichia coli produces cellular damage associated with fodrin disruption

Pet toxin is a serine protease from enteroaggregative Escherichia coli which has been described as causing enterotoxic and cytotoxic effects. In this paper we show that Pet produces spectrin and fodrin (nonerythroid spectrin) disruption. Using purified erythrocyte membranes treated with Pet toxin, we observed degradation of alpha- and beta-spectrin chains; this effect was dose and time dependent, and a 120-kDa protein fraction was observed as a breakdown product. Spectrin degradation and production of the 120-kDa subproduct were confirmed using specific antibodies against the alpha- and beta-spectrin chains. The same degradation effect was observed in alpha-fodrin from epithelial HEp-2 cells, both in purified cell membranes and in cultured cells which had been held in suspension for 36 h; these effects were confirmed using antifodrin rabbit antibodies. The spectrin and fodrin degradation caused by Pet is related to the Pet serine protease motif. Fluorescence and light microscopy of HEp-2 Pet-treated cells showed morphological alterations, which were associated with irregular distribution of fodrin in situ. Spectrin and fodrin degradation by Pet toxin were inhibited by anti-Pet antibodies and by phenylmethylsulfonyl fluoride. A site-directed Pet mutant, which had been shown to abolish the enterotoxic and cytotoxic effects of Pet, was unable to degrade spectrin in erythrocyte membranes or purified spectrin or fodrin in epithelial cell assays. This is a new system of cellular damage identified in bacterial toxins which includes the internalization of the protease, induction of some unknown intermediate signaling steps, and finally the fodrin degradation to destroy the cell.

On the role of the N-terminal group in the allosteric function of glucosamine-6-phosphate deaminase from Escherichia coli

Glucosamine-6-phosphate deaminase (EC 3.5.99.6) from Escherichia coli is an allosteric enzyme of the K-type, activated by N-acetylglucosamine 6-phosphate. It is a homohexamer and has six allosteric sites located in clefts between the subunits. The amino acid side-chains in the allosteric site involved in phosphate binding are Arg158, Lys160 and Ser151 from one subunit and the N-terminal amino group from the facing polypeptide chain. To study the functional role of the terminal amino group, we utilized a specific non-enzymic transamination reaction, and we further reduced the product with borohydride, to obtain the corresponding enzyme with a terminal hydroxy group. Several experimental controls were performed to assess the procedure, including reconditioning of the enzyme samples by refolding chromatography. Allosteric activation by N-acetylglucosamine 6-phosphate became of the K-V mixed type in the transaminated protein. Its kinetic study suggests that the allosteric equilibrium for this modified enzyme is displaced to the R state, with the consequent loss of co-operativity. The deaminase with a terminal hydroxy acid, obtained by reducing the transaminated enzyme, showed significant recovery of the catalytic activity and its allosteric activation pattern became similar to that found for the unmodified enzyme. It had lost, however, the pH-dependence of homotropic co-operativity shown by the unmodified deaminase in the pH range 6-8. These results show that the terminal amino group plays a part in the co-operativity of the enzyme and, more importantly, indicate that the loss of this co- operativity at low pH is due to the hydronation of this amino group.

Aggregation, dissociation and unfolding of glucose dehydrogenase during urea denaturation

The effect of urea on glucose dehydrogenase from Bacillus megaterium has been studied by following changes in enzymatic activity, conformation and state of aggregation. It was found that the denaturation process involves several transitions. At very low urea concentrations (below 0.5 M), where the enzyme is fully active and tetrameric, there is a conformational change as monitored by an increase in intensity of the tryptophan fluorescence and a maximum exposure of organized hydrophobic surfaces as reported by the fluorescence of 4,4'-dianilino-1,1'-binaphthyl-5.5'-disulfonic acid. At slightly higher urea concentrations (0.75-2 M), a major conformational transition occurs, as monitored by circular dichroism and fluorescence measurements, in which the enzyme activity is completely lost and is concomitant with the formation of interacting intermediates that lead to a highly aggregated state. Increasing urea concentrations cause a complete dissociation to lead first a partially and eventually the complete unfolded monomer. These phenomena are fully reversible by dilution of denaturant. It is concluded that after urea denaturation, the folding/assembly pathway of glucose dehydrogenase occurs with the formation of intermediate species in which transient higher aggregates appear to be involved.

Crystallization and preliminary crystallographic analysis of N-acetylglucosamine 6-phosphate deacetylase from Escherichia coli

N-Acetylglucosamine 6-phosphate deacetylase (E.C. 3.5.1.25), an enzyme from Escherichia coli involved in aminosugar catabolism, has been crystallized by the vapour-diffusion technique using phosphate as precipitant. X-ray diffraction experiments show the crystals to belong to the orthorhombic crystal system, with space group P2(1)2(1)2. The unit-cell parameters are a = 82.09 (2), b = 114.50 (1), c = 80.17 (1) A. The crystals diffract to a maximum resolution of 1.8 A and an initial data set was collected to 2.0 A.

Characterization of calreticulin as a protein interacting with protein kinase C

A protein kinase C (PKC)-binding protein was purified to homogeneity from the Triton-insoluble fraction from rat hepatocytes homogenates. The protein was identified as the mature calreticulin chain by N-terminal amino acid sequencing and by its immunoreactivity with anti-calreticulin antibody raised against the C-terminal KDEL (single-letter code) sequence. The calculated molecular mass was 46. 6 kDa but the protein migrates in SDS/PAGE as a doublet with apparent molecular masses of 60 and 55 kDa. Studies in vitro with purified calreticulin with the use of an overlay assay approach demonstrated that it binds to activated PKC isoenzymes expressed in rat hepatocytes. Phosphorylation of purified calreticulin with a PKC isoenzyme-specific immune complex kinase assay showed that it is also a very good substrate for all PKC isoforms in vitro. The treatment of intact cells with phorbol ester or with adrenaline (epinephrine) plus propranolol increased calreticulin phosphorylation, which was blocked by the pretreatment of cells with the PKC-specific inhibitor Ro 31-8220. The analysis of calreticulin immunoprecipitates from control or treated cells indicated that PKCalpha, PKCbeta, PKCtheta;, PKCzeta and PKCmu, but not PKCdelta or PKCepsilon, co-immunoprecipitated with calreticulin. Taken together, our results indicate that PKC interacts in vivo with calreticulin and suggest that they can operate in common signalling pathways.

Characterization of GP39-42 and GP24 antigens from Taenia solium cysticerci and of their antigenic GP10 subunit

Diagnosis of neurocysticercosis is performed by Western blotting with an enriched fraction of glycoproteins (LLGP). GP39-42 and GP24 are immunodominant antigens. These antigens were electroeluted and characterized by biochemical methods. When GP39-42 or GP24 were reduced, a band of 10 kDa (named GP10) appeared; this band was also analyzed. The most abundant amino acids in the three GPs were lysine, phenylalanine, asparagine, glycine, and leucine. The amino terminal portion was sequenced, and the following order was obtained for the three GPs: EKNKPKNVAXSTKKGYEYVXEF. The glycan portion was 8.4%, 18.2%, and 18.3% in GP39-42, GP24, and GP10, respectively. The three GPs contained mannose, N-acetyl-D-glucosamine, and galactose. GP39-42 and GP24 seem to be oligomeric forms of GP10. When reduced LLGP was reacted with samples obtained from patients with neurocysticercosis or pigs with cysticercosis, a band corresponding to GP10 was always observed. Furthermore, hyperimmune serum from rabbits immunized with GP39-42 or with GP24 recognized GP10 as well as GP39-42 and GP24. The data obtained in this paper suggest that GP10 might be a useful tool for diagnosis.

Rapid purification and properties of betaine aldehyde dehydrogenase from Pseudomonas aeruginosa

Betaine aldehyde dehydrogenase (BADH) (EC 1.2.1.8) catalyzes the last, irreversible step in the synthesis of the osmoprotectant glycine betaine from choline. In Pseudomonas aeruginosa this reaction is also an obligatory step in the assimilation of carbon and nitrogen when bacteria are growing in choline or choline precursors. We present here a method for the rapid purification to homogeneity of this enzyme by the use of ion-exchange and affinity chromatographies on 2',5'-ADP-Sepharose, which results in a high yield of pure enzyme with a specific activity at 30 degreesC and pH 7.4 of 74.5 U/mg of protein. Analytical ultracentrifugation, gel filtration, chemical cross-linking, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggest that BADH from P. aeruginosa is a homodimer with 61-kDa subunits. The amino acid composition and the N-terminal sequence of 21 amino acid residues showed significant similarity with those of the enzymes from Xanthomonas translucens and Escherichia coli. Neither BADH activity nor BADH protein was found in cell extracts from bacteria grown in the absence of choline. In contrast to other BADHs studied to date, the Pseudomonas enzyme cannot use positively charged aldehydes other than betaine aldehyde as substrates. The oxidation reaction has an activation energy of 39.8 kJ mol-1. The pH dependence of the velocity indicated an optimum at pH 8.0 to 8.5 and the existence of two ionizable groups with macroscopic pK values of 7.0 +/- 0.1 and 9. 7 +/- 0.1 involved in catalysis and/or binding of substrates. The enzyme is inactivated at 40 degreesC, but activity is regained when the heated enzyme is cooled to 30 degreesC or lower. At the optimum pH of 8.0, the enzyme is inactivated by dilution, but it is stable at pH 6.5 even at very low concentrations. Also, P. aeruginosa BADH activity is rapidly lost on removal of K+. In all cases studied, inactivation involves a biphasic process, which was dependent on the enzyme concentration only in the case of inactivation by dilution. NADP+ considerably protected the enzyme against these inactivating conditions.

Thermal denaturation of glutathione reductase from cyanobacterium Spirulina maxima

The thermal unfolding of glutathione reductase (NAD[P]H:GSSG oxidoreductase EC 1.6.4.2.) from cyanobacterium Spirulina maxima was monitored by differential scanning calorimetry and circular dichroism at neutral pH. Covalent cross-linking of enzyme at different temperatures revealed dimer as the species undergoing the thermal transition. A single endotherm was observed, but its thermodynamic parameters showed dependence on the scan rate. In the transition zone, aggregation of the dimeric species was observed. Analysis of the enzyme heated at 80 degrees C revealed that the resultant species retained a high content of secondary structure. The addition of low concentrations of guanidinium hydrochloride resulted in a full cooperative thermal transition. A model in which the dimeric protein undergoes a partial unfolding in a kinetically controlled fashion is proposed, such that the experimental value of delta H(cal) results from the simultaneous occurrence of endothermic and exothermic events.

Human placental estradiol 17 beta-dehydrogenase: structural and catalytic changes during urea denaturation

The denaturation behavior of human placental estradiol 17 beta-dehydrogenase (EC 1.1.1.62) in urea was studied by following changes in enzyme activity, conformation and oligomeric state. Results showed that the native --> unfolded transition follows a complex pattern, in which changes in both secondary and tertiary structure are simultaneous with changes in the aggregation state of enzyme. At relatively low urea (< 3 M), a major conformational transition, as monitored by CD and fluorescence measurements, is concomitant with an expanded state of the enzyme that coincides with its inactivation and the formation of polymeric species. Protein structural changes were also monitored by using the hydrophobic probe 1-anilinonaphthalene-8-sulfonic acid. The combined data suggest the existence of a molten globule state of dimeric enzyme promoted by low urea concentrations. Dilution of urea at this stage results in a full recovery of the enzymatic activity as well as of the native dimeric structure. Between 3 and 5 M urea estradiol 17 beta-dehydrogenase exists as a mixture of high molecular mass species which may be resolved by electrophoresis. In this range of urea concentration, only minor conformational changes were detected, although inactivation becomes to be irreversible. Above 5 M urea a second conformational transition takes place. Electrophoretic analysis of cross-linked samples revealed this stage results in the complete dissociation of enzyme toward unfolded monomer. It is concluded that the inactivation and unfolding of estradiol 17 beta-dehydrogenase during denaturation by urea occurs with the formation of intermediate species with different stability in which a molten globule-like state appears to be involved. The irreversibility of the process above urea 3 M is explained as the inability of aggregated enzyme to dissociate into native dimers.

Detergent solubilization of 3 beta-hydroxysteroid dehydrogenase from dog pancreas

Functional 3 beta-hydroxysteroid dehydrogenase coupled with isomerase (3 beta-HSD) was extracted from dog pancreatic mitochondria by treatment with the zwitterionic detergent CHAPSO. Increasing concentrations of this detergent led to a progressive and simultaneous solubilization of the pregnene (C-21) and androstene (C-19) dehydrogenase activities. Optimal solubilization of both C-21 and C-19 3 beta-HSD activities was achieved at a detergent/protein ratio of 0.6 (w/w). One hundred thirty percent of the initial particulate enzyme activities were recovered in the 105,000 g supernatant fluid with a 2.5-fold increase in the enzymatic specific activities. The C-21/C-19 activity ratios were 1.3 for mitochondria and 1.39 for the solubilized preparation. The apparent Km values for steroid substrates were unchanged after solubilization. Treatment of the mitochondrial suspension with sodium deoxycholate, CTAB, Lubrol XW, Brij 58, Emulgen 913 and Triton X-100 markedly decreased the 3 beta-HSD activities as a function of the detergent concentration and failed in to achieve solubilization.

Human placental 17 beta-hydroxysteroid dehydrogenase: secondary structure and circular dichroism demonstration of conformational changes upon NADP binding

The secondary structure of human placental 17 beta-hydroxysteroid dehydrogenase in the absence and presence of NADP has been studied by circular dichroism spectroscopy. The conformational analysis of the NADP-containing enzyme shows that is an alpha/beta protein with 60% of regular secondary structure (38% of alpha helix, 22% of beta-strand structures), 20% of beta-turn and 20% of non-repetitive structure. These results were in good agreement with the information obtained using statistical and homology methods based on amino-acid sequence. On the other hand, 25% alpha-helix, 55% beta-strand, and 20% non-repetitive structure were estimated by circular dichroism for the cofactor-free enzyme. Addition of varying concentrations of NADP to the cofactor free enzyme is accompanied by circular dichroism spectral changes. From the variation in the magnitude of the positive band at 193 nm with increasing NADP concentration, a dissociation constant of 34 nM was obtained.

Denaturing behavior of glutathione reductase from cyanobacterium Spirulina maxima in guanidine hydrochloride

The influence of guanidine hydrochloride (Gdn-HCl) on glutathione reductase from Spirulina maxima has been studied by measuring the changes in enzymatic activity, protein fluorescence, circular dichroism, thiol groups accessibility, and gel filtration chromatography. It was found that the denaturation process involves several intermediate states. At low, Gdn-HCl concentrations (Cm = 0.4 M), reductase activity was fully lost. However, below 3 M Gdn-HCl, this inhibition was freely reversible upon removal of the denaturing agent. Gel filtration experiments revealed that this reversible inhibition was not due to dissociation of the tetrameric enzyme. Structural studies strongly suggest that the conformation of this intermediate state is similar to that of native enzyme. A model in which a local region of the polypeptide chain assumes an extended conformation (D. T. Haynie, and E. Freire, Proteins 16,115-140) is proposed for the reversibly inactivated enzyme. Between 3 and 4 M Gdn-HCl (Cm = 3.5), the enzyme activity was irreversibly lost, this inhibition being concomitant with the loss of ellipticity, changes in both wavelength and intensity at the maximum of fluorescence emission, and dissociation of the enzyme into unfolded monomers; these results reveal that gross changes in the protein conformation occur under these conditions. At 4 M Gdn-HCl an equilibrium exists between the denatured forms of dimer and monomer, which is completely shifted toward the unfolded monomers at 5 M Gdn-HCl. Irreversibility in the Gdn-HCl-induced denaturation of S. maxima glutathione reductase was not due to aggregation of the unfolded enzyme.

Effect of inorganic phosphate on the self-associating properties of glutathione reductase from Spirulina maxima

In the presence of millimolar concentrations of inorganic phosphate, native Spirulina maxima glutathione reductase (NAD[P]H:GSSG oxidoreductase EC 1.6.4.2.) changes its aggregation state. The oligomeric structure of the enzyme was notably dependent upon phosphate molarity, ranging from a dimer-tetramer equilibrium at relatively low phosphate concentrations into a tetramer-octamer equilibrium at moderate or high phosphate concentrations. In spite of the changes in quaternary structure, the tetramer remains as the most stable and abundant species. Sodium chloride solutions were not able to produce a similar effect, thus discarding an unspecific ionic strength effect.

Purification and characterization of glutathione reductase from Rhodospirillum rubrum

Glutathione reductase (NAD(P)H:GSSG oxidoreductase EC 1.6.4.2.) was purified 1160-fold to homogeneity from the nonsulfurous purple bacteria Rhodospirillum rubrum (wild type). Specific activity of the pure preparation was 102 U/mg. The enzyme displayed a typical flavoprotein absorption spectrum with maxima at 274,365, and 459 nm and an absorbance ratio A280/A459 of 7.6. The amino acid analysis revealed an unusually high content of glycine and arginine residues. Titration of the enzyme with 5,5'-dithiobis(2-nitrobenzoic acid) showed a total of two free thiol groups per subunit, one of which is made accessible only under denaturing conditions. An isoelectric point of 5.2 was found for the native enzyme. Km values, determined at pH 7.5, were 6.1 and 90 microM for NADPH and GSSG, respectively. NADH was about 2% as active as NADPH as an electron donor. The enzyme's second choice in disulfide substrate was the mixed disulfide of coenzyme A and glutathione, for which the specific activity and Km values were 5.1 U/mg and 3.4 mM, respectively. A native molecular weight of 118,000 was found, while denaturing electrophoresis gave a value of 54,400 per subunit, thus suggesting that R. rubrum glutathione reductase exists as a dimeric protein. Other physicochemical constants of the enzyme, such as Stokes radius (4.2 nm) and sedimentation coefficient (5.71 S), were also consistent with a particle of 110,000.

Stability and activity of 20 beta-hydroxysteroid dehydrogenase in microemulsion of non-ionic detergents

We report here the formation of a microemulsion with non-ionic detergents and cyclohexane. The activity and stability of 20 beta-hydroxysteroid dehydrogenase solubilized in all water systems and in microemulsions of Nonidet P-40: Triton X-35/water/cyclohexane was investigated. In the microemulsion the activity depended on the molecular ratio of water to surfactant (Wo); maximal activity was obtained at Wo of 8.4. The stability in the microemulsion was higher at Wo = 11.75 i.e. the enzyme, retained about 50% of activity after eight days.

Delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity in canine pancreas

Activity of delta 5-3 beta-hydroxysteroid dehydrogenase coupled with steroid-delta 5-4-isomerase was demonstrated for the first time in the pancreas. The enzyme complex was assayed by measuring the conversion of pregnenolone to progesterone as well as of dehydroepiandrosterone to androstenedione and found to be localized primarily in the mitochondrial fraction of dog pancreas homogenates. The delta 5-3 beta-hydroxysteroid dehydrogenase used either NAD+ or NADP+ as co-substrates, although maximal activity was observed with NAD+. In phosphate buffer, pH 7.0 and 37 degrees C, the apparent Km values of the dehydrogenase were 6.54 +/- 0.7 microM for pregnenolone and 9.61 +/- 0.8 microM for NAD+. The apparent Vmax was determined as 0.82 +/- 0.02 nmol min-1 mg-1. Under the same conditions the Km values for dehydroepiandrosterone and NAD+ were 3.3 +/- 0.2 microM and 9.63 +/- 1.6 microM, respectively, and the apparent Vmax was 0.62 +/- 0.01 nmol min-1 mg-1.

Dimer-tetramer equilibrium of glutathione reductase from the cyanobacterium Spirulina maxima

Glutathione reductase [NAD(P)H:GSSG oxidoreductase; EC 1.6.4.2] from cyanobacterium Spirulina maxima exists as an equilibrium system between a dimer (S20,W = 5.96) and a tetramer (S20,W = 8.49) which has a very slow interconversion rate at neutral pH. Our results showed that the apparent dissociation constant (kd) was 4.61 X 10(-7) M. The proportion of both forms at pH 7.0 did not alter at either 4 or 25 degrees C. However, electrophoretic analysis at various pH values showed that at 25 degrees C a gradual transition takes place between oligomers with an apparent pKa of 7.55. When dimers aggregate to form tetramers, the reaction involves the uptake of eight protons (K = 1.58 X 10(-64) M9). At pH 7.7, the equilibrium shifts completely from dimers-tetramers to dimers when temperature is increased, which would suggest that the dissociation is an endothermic process. Thermodynamic parameters obtained from the temperature study show that the dissociation of glutathione reductase is characterized by positive entropy and enthalpy changes. Neither NADPH nor GSSG have any effect on the dimer-tetramer equilibrium. Measurements of reductase activity indicate that the tetramer is almost certainly active, whereas the dimer is either less active or inactive.

17 beta-hydroxysteroid dehydrogenase activity in canine pancreas

The mitochondrial fraction of the dog pancreas showed NAD(H)-dependent enzyme activity of 17 beta-hydroxysteroid dehydrogenase. The enzyme catalyzes oxidoreduction between androstenedione and testosterone. The apparent Km value of the enzyme for androstenedione was 9.5 +/- 0.9 microM, the apparent Vmax was determined as 0.4 nmol mg-1 min-1, and the optimal pH was 6.5. In phosphate buffer, pH 7.0, maximal rate of androstenedione reduction was observed at 37 degrees C. The oxidation of testosterone by the enzyme proceeded at the same rate as the reduction of the androstenedione at a pH of 6.8-7.0. The apparent Km value and the optimal pH of the enzyme for testosterone were 3.5 +/- 0.5 microM and 7.5, respectively.

Periodate-oxidized NADP+ is a powerful inhibitor of human placental estradiol-17 beta dehydrogenase

Periodate-oxidized NADP+ inhibits the NAD+-linked activity of human placental estradiol-17 beta dehydrogenase (EC 1.1.1.62). The inhibition appears to be competitive with respect to NAD+ and can be reversed by dialysis or gel filtration. The apparent inhibitor constant for the periodate-oxidized analogue is 0.047 microM. The presence in the incubation mixture of NAD+ protects the enzyme against inhibition. No inhibitory effects of the coenzyme analogue are observed on the NADP+-linked activity of the enzyme.

Purification, properties, and oligomeric structure of glutathione reductase from the cyanobacterium Spirulina maxima

Glutathione reductase [NAD(P)H:GSSG oxidoreductase EC 1.6.4.2] from cyanobacterium Spirulina maxima was purified 1300-fold to homogeneity by a simple three-step procedure involving ammonium sulfate fractionation, ion exchange chromatography on DEAE-cellulose, and affinity chromatography on 2',5'-ADP-Sepharose 4B. Optimum pH was 7.0 and enzymatic activity was notably increased when the phosphate ion concentration was increased. The enzyme gave an absorption spectrum that was typical for a flavoprotein in that it had three peaks with maximal absorbance at 271, 370, and 460 nm and a E1%271 of 23.3 Km values were 120 +/- 12 microM and 3.5 +/- 0.9 microM for GSSG and NADPH, respectively. Mixed disulfide of CoA and GSH was also reduced by the enzyme under assay conditions, but the enzyme had a very low affinity (Km 3.3 mM) for this substrate. The enzyme was specific for NADPH. The isoelectric point of the native enzyme at 4 degrees C was 4.35 and the amino acid composition was very similar to that previously reported from other sources. The molecular weight of a subunit under denaturing conditions was 47,000 +/- 1200. Analyses of pure enzyme by a variety of techniques for molecular weight determination revealed that, at pH 7.0, the enzyme existed predominantly as a tetrameric species in equilibrium with a minor dimer fraction. Dissociation into dimers was achieved at alkaline pH (9.5) or in 6 M urea. However, the equilibrium at neutral pH was not altered by NADPH or by disulfide reducing reagents. The Mr and S20,w of the oligomeric enzyme were estimated to be 177,000 +/- 14,000 and 8.49 +/- 0.5; for the dimer, 99,800 +/- 7000 and 5.96 +/- 0.4, respectively. Low concentrations of urea increased the enzymatic activity, but this increase was not due to changes in the proportions of both forms.

A single step procedure for purification of estradiol 17 beta-dehydrogenase from human placenta

A new and simple procedure for purification to homogeneity of the soluble estradiol 17 beta-dehydrogenase [E C.1.1.1.62] from human placenta has been developed. The purification is achieved in a single step by affinity-absorption of Cibachrome Blue F3G-A coupled to Sepharose and selective elution with NADP+. Homogeneous estradiol 17 beta-dehydrogenase has a specific activity of 7.2 units/mg. and has been purified 2400-fold with a 93% recovery.

Dehydroepiandrosterone is a substrate for estradiol 17 beta-dehydrogenase from human placenta

The enzyme estradiol 17 beta-dehydrogenase (17 beta-ED) [E.C.1.1.1.62] from human placenta was purified to homogeneity by the initial steps of a published procedure, followed by an affinity chromatography step in Reactive Blue 2-Sepharose, eluting with NADP. The pure enzyme is not specific for estrogenic substrates, it also catalyzes the oxidation-reduction of several androgens and progesterone (i.e. dehydroepiandrosterone, androstenedione, 5 alpha-dihydrotestosterone, and 20 alpha-dihydroprogesterone). The comparison of the kinetic parameters for these substrates, shows that dehydroepiandrosterone could be a physiological ligand of the enzyme, and consequently involved in the control of its function in estrogen metabolism.