Purification and Characterization of Albumin from Frog Skin of <Emphasis Type="Italic">Duttaphrynus melanostictus</Emphasis>

Following determination of trypsin inhibitory activity, a serine protease inhibitor was purified and characterized from frog Duttaphrynus melanostictus serum. It was identified as serum albumin, with molecular weight of 67 kDa (DmA-serum). Different from bovine serum albumin, DmA-serum potently inhibited trypsin with similar K _i values around 1.6 × 10⁻⁷ M. No inhibitory effect on thrombin, chymotrypsin, elastase and subtilisin was observed under the assay conditions. The N-terminal amino acid is EAEPHSRI. Subsequently, a protein with same N-terminal amino acid was purified from skin, termed as DmA-skin. However, DmA-skin is distinct from DmA-serum by binding of a haem b (0.5 mol/mol protein), and with low trypsin inhibitory activity. Frog albumin is distributed in frog skin and exhibited trypsin inhibitory activity, suggesting that it plays important roles in skin physiological functions, like water economy, metabolite exchange and osmoregulation, etc.     

A trypsin inhibitor from <Emphasis Type="Italic">Cassia obtusifolia</Emphasis> seeds: isolation,characterization and activity against <Emphasis Type="Italic">Pieris rapae</Emphasis>

A trypsin inhibitor was isolated from Cassia obtusifolia by ammonium sulfate precipitation, Sepharose 4B-trypsin affinity and Sephadex G-75 chromatography. The inhibitor consisted of a single polypeptide chain with a molecular mass of 19, 812.55 Da. It was stable from pH 2 to 12 for 24 h, whereas it was unstable either above 70°C for 10 min or under reduced conditions. The inhibitor, which inhibited trypsin activity with an apparent Ki of 0.3 μM, had one reactive site involving a lysine residue. The native inhibitor was resistant to pepsin digestion, whereas the heated inhibitor produced 40% degree of susceptibility. The disulfide linkage and lysine residue were important in maintaining its conformation. Partial amino acid sequence of the purified protein showed a high degree of homology with various members of the Kunitz inhibitor family. Moreover, the inhibitor showed significant inhibitory activity against trypsin-like proteases present in the larval midgut on Pieris rapae and could suppress the growth of larvae.     

Substrate specificity characterization of a thermostable keratinase from <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> KS-1

A feather-degrading strain of Pseudomonas aeruginosa KS-1 was used in the present study. Its crude cell-free fermentation broth completely degraded chicken feather within 12 h, in the absence of disulphide reductase activity. Keratinase from its extracellular broth was purified and characterized, assuming that it would be a potential β-keratin-degrading enzyme with prospective applications in degradation of β-plaques of prions. The keratinase was purified by using Q-Sepharose anion exchange chromatography and its molecular weight, as determined by SDS–PAGE analysis, was 45 kDa. It was an alkaline, serine protease with pH and temperature optima of 9 and 60°C, respectively. The enzyme was highly thermostable with a t _1/2 > 2 h at 80°C and had a very high K to C (keratinolytic to caseinolytic) ratio of 2.5. Besides feather keratin, it also hydrolyzed a variety of other complex substrates including fibrin, gelatin and meat protein. Its activity on synthetic substrates revealed that it efficiently cleaves them in the order phenylalanine > lysine > alanine > leucine p-nitroanilides. It also cleaved insulin B chain between Val¹²-Glu¹³, Ala¹⁴-Leu¹⁵, Gly²⁰-Glu²¹ and Arg²²-Gly²³ residues.     

Biochemical characterization of the carotenoid 1,2-hydratases (CrtC) from <Emphasis Type="Italic">Rubrivivax gelatinosus</Emphasis> and <Emphasis Type="Italic">Thiocapsa roseopersicina</Emphasis>

Two carotenoid 1,2-hydratase (CrtC) genes from the photosynthetic bacteria Rubrivivax gelatinosus and Thiocapsa roseopersicina were cloned and expressed in Escherichia coli in an active form and purified by affinity chromatography. The biochemical properties of the recombinant enzymes and their substrate specificities were studied. The purified CrtCs catalyze cofactor independently the conversion of lycopene to 1-HO- and 1,1′-(HO)₂-lycopene. The optimal pH and temperature for hydratase activity was 8.0 and 30°C, respectively. The apparent K _m and V _max values obtained for the hydration of lycopene were 24 μM and 0.31 nmol h⁻¹ mg⁻¹ for RgCrtC and 9.5 μM and 0.15 nmol h⁻¹ mg⁻¹ for TrCrtC, respectively. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis revealed two protein bands of 44 and 38 kDa for TrCrtC, which indicate protein processing. Both hydratases are also able to convert the unnatural substrate geranylgeraniol (C20 substrate), which functionally resembles the natural substrate lycopene.     

Kunitz-type trypsin inhibitor with high stability from <Emphasis Type="Italic">Spinacia oleracea</Emphasis> L. seeds

The trypsin inhibitor SOTI was isolated from Spinacia oleracea L. seeds through ammonium sulfate precipitation, Sepharose 4B-trypsin affinity chromatography, and Sephadex G-75 chromatography. This typical Kunitz inhibitor showed remarkable stability to heat, pH, and denaturant. It retained 80% of its activity against trypsin after boiling for 20 min, and more than 90% activity when treated with 6 M guanidine hydrochloride. The formation of stable SOTI-trypsin complex (K _i = 2.3·10⁻⁶ M) is consistent with significant inhibitory activity of SOTI against trypsin-like proteinases present in the larval midgut of Pieris rapae. Sequences of SOTI fragments showed homology with other inhibitors. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 1, pp. 131–140.     

Desulforubrerythrin from <Emphasis Type="Italic">Campylobacter jejuni</Emphasis>, a novel multidomain protein

A novel multidomain metalloprotein from Campylobacter jejuni was overexpressed in Escherichia coli, purified, and extensively characterized. This protein is isolated as a homotetramer of 24-kDa monomers. According to the amino acid sequence, each monomer was predicted to contain three structural domains: an N-terminal desulforedoxin-like domain, followed by a four-helix bundle domain harboring a non-sulfur μ-oxo diiron center, and a rubredoxin-like domain at the C-terminus. The three predicted iron sites were shown to be present and were studied by a combination of UV–vis, EPR, and resonance Raman spectroscopies, which allowed the determination of the electronic and redox properties of each site. The protein contains two FeCys₄ centers with reduction potentials of +240 mV (desulforedoxin-like center) and +185 mV (rubredoxin-like center). These centers are in the high-spin configuration in the as-isolated ferric form. The protein further accommodates a μ-oxo-bridged diiron site with reduction potentials of +270 and +235 mV for the two sequential redox transitions. The protein is rapidly reoxidized by hydrogen peroxide and has a significant NADH-linked hydrogen peroxide reductase activity of 1.8 μmol H₂O₂ min⁻¹ mg⁻¹. Owing to its building blocks and its homology to the rubrerythrin family, the protein is named desulforubrerythrin. It represents a novel example of the large diversity of the organization of domains exhibited by this enzyme family.     

Purification and biological characterization of a halophilic thermostable protease from <Emphasis Type="Italic">Haloferax lucentensis</Emphasis> VKMM 007

An extremely halophilic archaeon Haloferax lucentensis VKMM 007, isolated from a solar saltern, was found to produce a protease. This extracellular enzyme consisted of a single polypeptide chain of 57.8 kDa as determined by SDS–PAGE and was purified by a combination of ultrafiltration, bacitracin–Sepharose affinity chromatography and Sephadex G-100 gel filtration. The purified protein was stable in a wide range of temperatures (20–70°C), NaCl concentrations (0.85–5.13 M) and pH (5.0–9.0) with maximal activity observed at 60°C, 4.3 M NaCl and pH 8.0. Proteolytic activity was enhanced by Ca²⁺, K⁺, Mg²⁺, Na⁺, and Fe²⁺ ions and the protein was classified as a trypsin-like serine protease. Further assays indicated highest degree of specificity when hemoglobin was used as an enzyme substrate. Most importantly, the proteolytic activity remained stable or only marginally inhibited in the presence of various polar and non-polar solvents, surfactants and reducing agents thus emphasizing the biotechnological potential of this novel halophilic protease.     

Molecular characterization of phenylalanine ammonia lyase gene from <Emphasis Type="Italic">Cistanche deserticola</Emphasis>

We cloned the gene, CdPAL1, from Cistanche deserticola callus using RACE PCR with degenerate primers that were designed based on a multiple sequence alignment of known PAL genes from other plant species. The gene shows high homology to other known PAL genes registered in GenBank. The recombinant protein exhibited Michaelis–Menten kinetics with a K _m of 0.1013 mM, V _max of 4.858 μmol min⁻¹, K _cat of 3.36 S⁻¹, and K _cat/K _m is 33,168 M⁻¹ S⁻¹. The enzyme had an optimal pH of 8.5 and an activation energy of 38.92 kJ mol⁻¹ when l-Phenylalanine was used as a substrate; l-tyrosine cannot be used as substrate for this protein. The optimal temperature was 55°C, and the thermal stability results showed that, after a treatment at 70°C for 20 min, the protein retained 87% activity, while a treatment at 75°C for 20 min resulted in a loss of over 85% of the enzyme activity. Treatment with heavy metal ions (Hg²⁺, Pb²⁺, and Zn²⁺) showed remarkable inhibitory effects. Among the intermediates from the lignin (cinnamyl alcohol, cinnamyl aldehyde, coniferyl aldehyde, coniferyl alcohol), phenylpropanoid (cinnamic acid, coumaric acid, caffeic acid, and chlorogenic acid) and phenylethanoid (tyrosol and salidroside) biosynthetic pathways, only cinnamic acid showed strong inhibitory effects against CdPAL1 activity with a K _i of 8 μM. Competitive inhibitor AIP exhibited potent inhibition with K _i = 0.056 μM.     

Production,purification and characterization of a thermostable laccase from a tropical white-rot fungus

A thermostable laccase was isolated from a tropical white-rot fungus Polyporus sp. which produced as high as 69,738 units of laccase l⁻¹ in an optimized medium containing 20 g of malt extract l⁻¹, 2 g of yeast extract l⁻¹, 1.5 mM CuSO₄. The laccase was purified to electrophoretic purity with a final purification of 44.70-fold and a recovery yield of 21.04%. The purified laccase was shown to be a monomeric enzyme with a molecular mass of 60 kDa. The optimum temperature and pH value of the laccase were 75°C and pH 4.0, respectively, for 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS). The Michaelis–Menten constant (K _m ) of the laccase was 18 μM for ABTS substrate. The laccase was stable at pH values between 5.5 and 7.5. About 80% of the initial enzyme activity was retained after incubation of the laccase at 70°C for 2 h, indicating that the laccase was intrinsically highly thermostable and with valuable potential applications. The laccase activity was promoted by 4.0 mM of Mg²⁺, Mn²⁺, Zn²⁺ and Ca²⁺, while inhibited by 4.0 mM of Co²⁺, Al³⁺, Cu²⁺, and Fe²⁺, showing different profiles of metal ion effects.     

Characterization of <Emphasis Type="Italic">Deinococcus radiophilus</Emphasis> thioredoxin reductase active with both NADH and NADPH

Thioredoxin reductase (TrxR, EC 1.6.4.5) of Deinococcus radiophilus was purified by steps of sonication, ammonium sulfate fractionation, 2′5′ ADP Sepharose 4B affinity chromatography, and Sephadex G-100 gel filtration. The purified TrxR, which was active with both NADPH and NADH, gave a 368 U/mg protein of specific activity with 478-fold purification and 18% recovery from the cell-free extract. An isoelectric point of the purified enzymes was ca. 4.5. The molecular weights of the purified TrxR estimated by PAGE and gel filtration were about 63.1 and 72.2 kDa, respectively. The molecular mass of a TrxR subunit is 37 kDa. This suggests that TrxR definitely belongs to low molecular weight TrxR (L-TrxR). The Km and Vmax of TrxR for NADPH are 12.5 μM and 25 μM/min, whereas those for NADH are 30.2 μM and 192 μM/min. The Km and Vmax for 5, 5′-dithio-bis-2-nitrobenzoic acid (DTNB, a substituted substrate for thioredoxin) are 463 μM and 756 μM/min, respectively. The presence of FAD in TrxR was confirmed with the absorbance peaks at 385 and 460 nm. The purified TrxR was quite stable from pH 3 to 9, and was thermo-stable up to 70°C. TrxR activity was drastically reduced (ca. 70%) by Cu²⁺, Zn²⁺, Hg²⁺, and Cd²⁺, but moderately reduced (ca. 50%) by Ag⁺. A significant inhibition of TrxR by N-ethylmaleimide suggests an occurrence of cysteine at its active sites. Amino acid sequences at the N-terminus of purified TrxR are H₂N-Ser-Glu-Gln-Ala-Gln-Met-Tyr-Asp-Val-Ile-Ile-Val-Gly-Gly-Gly-Pro-Ala-Gly-Leu-Thr-Ala-COOH. These sequences show high similarity with TrxRs reported in Archaea, such as Methanosarcina mazei, Archaeoglobus fulgidus etc.     

Isolation and characterization of Glyceraldehyde-3-phosphate dehydrogenase from the common octopus (<Emphasis Type="Italic">Octopus vulgaris </Emphasis>Cuvier, 1797)

The NAD⁺ dependent cytosolic Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) from arms of Octopus vulgaris, Cuvier, 1787, (Octopoda, Cephalopoda) was purified to homogeneity and its kinetic properties investigated. The purification method consisted of ammonium sulfate fractionation followed by Blue Sepharose CL-6B chromatography resulting in a 26-fold increase in specific activity and a final yield of approximately 16%. The apparent molecular weight of the purified native enzyme was 153 kDa. The protein is an homotetramer, composed of identical subunits with an apparent molecular weight of approximately 36 kDa. The Michaelis constants K_m for both NAD⁺ and d-G3P were 66 μM and 320 μM, respectively. The maximal velocity V_max of the purified enzyme was estimated to be 21.8 U/mg. Only one GAPDH isoform (pI 6.6) was obtained by isoelectrofocusing in polyacrylamide slab gels holding ampholyte generated pH gradients. Under the conditions of assay, the optimum activity occurs at pH 7.0 and at temperature of 35°C. Polyclonal antibodies raised in rabbits against the purified GAPDH immunostained a single 36 kDa GAPDH band on crude extract protein preparations blotted onto nitrocellulose.     

Purification,characterization and evaluation of insecticidal potential of trypsin inhibitor from mungbean (<Emphasis Type="Italic">Vigna radiata</Emphasis> L. Wilczek) seeds

Protease inhibitors present in seeds of legumes possess strong inhibitory activity against trypsin and confer resistance against pests. In the present investigation, trypsin inhibitor activity was found in the seed flour extracts of all the eight selected varieties of mungbean under study which was further confirmed by dot blot analysis. All the varieties showed inhibitory activity in vitro against the gut protease of Helicoverpa armigera (HGP). Trypsin inhibitor was purified from mungbean seeds to near homogeneity with 58.1-fold and 22.8% recovery using heat denaturation, NH₄(SO₄)₂ fractionation, ion-exchange chromatography on DEAE-Sephadex A-25 and gel filtration through Sephadex G-75. The molecular mass of the inhibitor was 47 kDa as determined by gel filtration and SDS-PAGE. The inhibitor retained 90% or more activity between pH 4 and 10, however, it was nearly inactive at extreme pH values. The inhibitor was stable up to 80°C but thereafter, the activity decreased gradually retaining nearly 30% of activity when heated at 100°C for 20 min. The inhibitor activity was undetectable at 121°C. Insect bioassay experiment using purified mungbean trypsin inhibitor showed a marked decline in survival (%) of larvae with increase in inhibitor concentration. The larval growth was also extended by the trypsin inhibitor. This study signifies the insecticidal potential of mungbean trypsin inhibitor which might be exploited for raising transgenic plants.     

Purification of the photosynthetic reaction center from <Emphasis Type="Italic">Heliobacterium modesticaldum</Emphasis>

We have developed a purification protocol for photoactive reaction centers (HbRC) from Heliobacterium modesticaldum. HbRCs were purified from solubilized membranes in two sequential chromatographic steps, resulting in the isolation of a fraction containing a single polypeptide, which was identified as PshA by LC–MS/MS of tryptic peptides. All polypeptides reported earlier as unknown proteins (in Heinnickel et al., Biochemistry 45:6756–6764, 2006; Romberger et al., Photosynth Res 104:293–303, 2010) are now identified by mass spectrometry to be the membrane-bound cytochrome c ₅₅₃ and four different ABC-type transporters. The purified PshA homodimer binds the following pigments: 20 bacteriochlorophyll (BChl) g, two BChl g′, two 8¹-OH-Chl a _F, and one 4,4′-diaponeurosporene. It lacks the PshB polypeptide binding the F_A and F_B [4Fe–4S] clusters. It is active in charge separation and exhibits a trapping time of 23 ps, as judged by time-resolved fluorescence studies. The charge recombination rate of the P₈₀₀ ⁺F_X⁻ state is 10–15 ms, as seen before. The purified HbRC core was able to reduce cyanobacterial flavodoxin in the light, exhibiting a K _M of 10 μM and a k _cat of 9.5 s⁻¹ under near-saturating light. There are ~1.6 menaquinones per HbRC in the purified complex. Illumination of frozen HbRC in the presence of dithionite can cause creation of a radical at g = 2.0046, but this is not a semiquinone. Furthermore, we show that high-purity HbRCs are very stable in anoxic conditions and even remain active in the presence of oxygen under low light.     

Purification and Characterization of Trypsin-like Enzymes from <Emphasis Type="Italic">Neomysis japonica</Emphasis> Using BApNA as Substrate

Using N-α-benzoyl-l-arginine p-nitroanilide (BApNA) as substrate, trypsin-like enzymes (TLEs) were purified from mysis (Neomysis japonica) following two chromatographic steps, Sephacryl S100 HR gel filtration and Benzamidine-Sepharose 4B affinity. They presented a high stability in the raw material, retaining over 45% of the initial activity after 30 days of storage at pH 8.0, 45 °C. The purified TLEs had relative molecular mass between 32 kDa and 33 kDa. With higher stability and greater activity, they had similar stability and activity profiles (pH 6.0–11.0, 15–65 °C) as bovine trypsin but had a different optimum temperature (35 °C for trypsin and 45 °C for TLEs). Similar to bovine trypsin, the purified TLEs could be activated by Ca²⁺ and Mg²⁺. And the purified TLEs also showed similar inhibitory profiles as bovine trypsin with the exception of chicken egg ovomucoid (CEOM), an effective inhibitor of bovine trypsin but less so for purified TLEs. Having TLEs with physiological efficiency 3.6 times that of bovine trypsin, the use of mysis as a source for commercial production of TLEs is discussed.     

A Novel Phytase appA from <Emphasis Type="Italic">Citrobacter amalonaticus</Emphasis> CGMCC 1696: Gene Cloning and Overexpression in <Emphasis Type="Italic">Pichia pastoris</Emphasis>

A novel phytase gene appA, with upstream and downstream sequences from Citrobacter amalonaticus CGMCC 1696, was cloned by degenerate polymerase chain reaction (PCR), and thermal asymmetric interlaced (TAIL) PCR and was overexpressed in Pichia pastoris. Sequence analysis revealed one open reading frame that consisted of 1311 bp encoding a 436–amino-acid protein, which had a deduced molecular mass of 46.3 kDa. The phytase appA belongs to the histidine acid phosphatase family and exhibits the highest identity (70.1%) with C. braakii phytase. The gene was overexpressed in P. pastoris. The secretion yield of recombinant appA protein was accumulated to approximately 4.2 mg·mL⁻¹, and the enzyme activity level reached 15,000 U·mL⁻¹, which is higher than any previous reports. r-appA was glycosylated, as shown by Endo H treatment. r-appA was purified and characterized. The specific activity of r-appA for sodium phytate was 3548 U·mg⁻¹. The optimum pH and temperature for enzyme activity were 4.5 and 55°C, respectively. r-appA was highly resistant to pepsin or trypsin treatment. This enzyme could be an economic and efficient alternative to the phytases currently used in the feed industry.     

Pr-1, a novel antifungal protein from pumpkin rinds

A novel antifungal protein, M_r = ca. 40 kDa, was isolated from pumpkin rind and designated Pr-1. When purified by anion exchange chromatography and HPLC, it inhibited growth of several fungi including Botrytis cinerea, Fusarium oxysporum, Fusarium solani and Rhizoctonia solani, as well as the yeast, Candida albicans, at 10–20 μM. It did not inhibit growth of Escherichia coli or Staphylococcus aureus even at 200 μM. Laser scanning microscopy of fungal cells exposed to rhodamine-labeled Pr-1 revealed that the protein accumulated and was localized on the cell surface. Uptake of the vital stain, SYTOX Green, was enhanced when fungal conidia were treated with Pr-1 suggesting that the protein has membrane permeabilization activity. Pr-1 was thermostable at 70°C and did not lyse human red blood cells at 128 μM suggesting that the protein may be useful as an antifungal agent with little, if any human cytotoxicity.     

Gene cloning and expression of a new acidic family 7 endo-β-1,3-1,4-glucanase from the acidophilic fungus Bispora sp. MEY-1

Most reported microbial β-1,3-1,4-glucanases belong to the glycoside hydrolase family 16. Here, we report a new acidic family 7 endo-β-1,3-1,4-glucanase (Bgl7A) from the acidophilic fungus Bispora sp. MEY-1. The cDNA of Bgl7A was isolated and over-expressed in Pichia pastoris, with a yield of about 1,000 U ml^–1 in a 3.7-l fermentor. The purified recombinant Bgl7A had three activity peaks at pH 1.5, 3.5, and 5.0 (maximum), respectively, and a temperature optimum at 60°C. The enzyme was stable at pH 1.0–8.0 and highly resistant to both pepsin and trypsin. Belonging to the group of non-specific endoglucanase, Bgl7A can hydrolyze not only β-glucan and cellulose but also laminarin and oat spelt xylan. The specific activity of Bgl7A against barley β-glucan and lichenan (4,040 and 2,740 U mg^–1) was higher than toward carboxymethyl cellulose sodium (395 U mg^–1), which was different from other family 7 endo-β-glucanases.     

Effect of trace metals on ethanol production from synthesis gas by the ethanologenic acetogen, <Emphasis Type="Italic">Clostridium</Emphasis><Emphasis Type="Italic">ragsdalei</Emphasis>

The effect of trace metal ions (Co²⁺, Cu²⁺, Fe²⁺, Mn²⁺, Mo⁶⁺, Ni²⁺, Zn²⁺, SeO₄ ⁻ and WO₄ ⁻) on growth and ethanol production by an ethanologenic acetogen, Clostridium ragsdalei was investigated in CO:CO₂-grown cells. A standard acetogen medium (ATCC medium no. 1754) was manipulated by varying the concentrations of trace metals in the media. Increasing the individual concentrations of Ni²⁺, Zn²⁺, SeO₄ ⁻ and WO₄ ⁻ from 0.84, 6.96, 1.06, and 0.68 μM in the standard trace metals solution to 8.4, 34.8, 5.3, and 6.8 μM, respectively, increased ethanol production from 35.73 mM under standard metals concentration to 176.5, 187.8, 54.4, and 72.3 mM, respectively. Nickel was necessary for growth of C. ragsdalei. Growth rate (μ) of C. ragsdalei improved from 0.34 to 0.49 (day⁻¹), and carbon monoxide dehydrogenase (CODH) and hydrogenase (H₂ase)-specific activities improved from 38.45 and 0.35 to 48.5 and 1.66 U/mg protein, respectively, at optimum concentration of Ni²⁺. At optimum concentrations of WO₄ ⁻ and SeO₄ ⁻, formate dehydrogenase (FDH) activity improved from 32.3 to 42.6 and 45.4 U/mg protein, respectively. Ethanol production and the activity of FDH reduced from 35 mM and 32.3 U/mg protein to 1.14 mM and 8.79 U/mg protein, respectively, upon elimination of WO₄ ⁻ from the medium. Although increased concentration of Zn²⁺ enhanced growth and ethanol production, the activities of CODH, FDH, H₂ase and alcohol dehydrogenase (ADH) were not affected by varying the Zn²⁺ concentration. Omitting Fe²⁺ from the medium decreased ethanol production from 35.7 to 6.30 mM and decreased activities of CODH, FDH, H₂ase and ADH from 38.5, 32.3, 0.35, and 0.68 U/mg protein to 9.07, 7.01, 0.10, and 0.24 U/mg protein, respectively. Ethanol production improved from 35 to 54 mM when Cu²⁺ was removed from the medium. The optimization of trace metals concentration in the fermentation medium improved enzyme activities (CODH, FDH, and H₂ase), growth and ethanol production by C. ragsdalei.     

Isolation and preliminary characterization of a respiratory nitrate reductase from hydrocarbon-degrading bacterium <Emphasis Type="Italic">Gordonia alkanivorans</Emphasis> S7

Gordonia alkanivorans S7 is an efficient degrader of fuel oil hydrocarbons that can simultaneously utilize oxygen and nitrate as electron acceptors. The respiratory nitrate reductase (Nar) from this organism has been isolated using ion exchange chromatography and gel filtration, and then preliminarily characterized. PAGE, SDS-PAGE and gel filtration chromatography revealed that Nar consisted of three subunits of 103, 53 and 25 kDa. The enzyme was optimally active at pH 7.9 and 40°C. K _m values for NO₃ ⁻ (110 μM) and for ClO₃ ⁻ (138 μM) were determined for a reduced viologen as an electron donor. The purified Nar did not use NADH as the electron donor to reduce nitrate or chlorate. Azide was a strong inhibitor of its activity. Our results imply that enzyme isolated from G. alkanivorans S7 is a respiratory membrane-bound nitrate reductase. This is the first report of purification of a nitrate reductase from Gordonia species.