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PubMed1999

Cloning, nucleotide sequence and expression of a new L-N-carbamoylase gene from Arthrobacter aurescens DSM 3747 in E. coli.

An L-N-carbamoyl amino acid amidohydrolase (L-N-carbamoylase) from Arthrobacter aurescens DSM 3747 was cloned in E. coli and the nucleotide sequence was determined. After expression of the gene in E. coli the enzyme was purified to homogeneity and characterized. The enzyme was shown to be strictly L-specific and exhibited the highest activity in the hydrolysis of beta-aryl substituted N alpha-carbamoyl-alanines as e.g. N-carbamoyl-tryptophan. Carbamoyl derivatives of beta-alanine and charged aliphatic amino acids were not accepted as substrates. The N-carbamoylase of A. aurescens DSM 3747 differs from all known enzymes with respect to its substrate specificity although amino acid sequence identity scores of 35-38% to other N-carbamoylases have been detected. The enzyme consists of two subunits of 44,000 Da, and has an isoelectric point of 4.3. The optima of temperature and pH were determined to be 50 degrees C and pH 8.5 respectively. At 37 degrees C the enzyme was completely stable for several days.

Amidohydrolases↗
PubMed1999

Purification, characterization, and application of an acid urease from Arthrobacter mobilis.

It has been shown that urea in fermented beverages and foods can serve as a precursor of ethylcarbamate, a potential carcinogen, and acid urease is an effective agent for removing urea in such products. We describe herein the purification and characterization of a novel acid urease from Arthrobacter mobilis SAM 0752 and show its unique application for the removal of urea from fermented beverages using the Japanese rice wine, sake, as an example. The purified acid urease showed an optimum pH for activity at pH 4.2. The enzyme exhibited an apparent K(m) for urea of 3.0 mM and a Vmax of 2370 mumol of urea per mg and min at 37 degrees C and pH 4.2. Gel permeation chromatographic and sodium dodecyl sulfate gel electrophoretic analyses showed that the enzyme has an apparent native molecular weight (M(r)) of 290,000 and consisted of three types of subunit proteins (M(r), 67,000, 16,600, 14,100) denoted by alpha, beta, and gamma. The most probable stoichiometry of the subunits was estimated to be alpha: beta: gamma = 1:1:1, suggesting the enzyme subunit structure of (alpha beta gamma)3. The enzyme also existed as an aggregated form with an M(r) of 580,000. The purified enzyme contained 2 g-atom of nickel per alpha beta gamma unit of the enzyme. Enzyme activity was inhibited by acetohydroxamic acid, HgCl2, and CuCl2. The isoelectric point of the native enzyme was estimated by gel electrofocusing to be 6.8. Urea (50 ppm), which was exogenously added to sake (pH 4.4, 17 +/- 1% (v/v) ethanol), was completely decomposed by incubation with the enzyme (0.09 U ml-1) at 15 degrees C for 13 days. The enzyme was unstable at temperatures higher than 65 degrees C and pHs lower than 4, and was completely inactivated under the conditions of a pasteurization step involved in the traditional sake-making processes. These results indicate that the enzyme is applicable to the elimination of urea in fermented beverages with minimal modification to the conventional process.

Alcoholic Beverages↗
PubMed2003

Branching of o-nitrobenzoate degradation pathway in Arthrobacter protophormiae RKJ100: identification of new intermediates.

We have earlier reported a novel reductive pathway for o-nitrobenzoate (ONB) degradation (at 0.5 mM) in Arthrobacter protophormiae RKJ100, which proceeds via the formation of o-hydroxylaminobenzoate (HABA) and anthranilate (AA). During growth of this organism at 40 times higher concentration (20 mM) of ONB, 3-hydroxyanthranilate (HAA) was identified as an intermediate by thin layer chromatography, gas chromatography and high performance liquid chromatography studies. Crude cell extracts of ONB-grown cells showed HAA 3,4-dioxygenase activity suggesting HAA as a terminal aromatic intermediate of the catabolic energy-yielding pathway as shown before in Pseudomonas fluorescens strain KU-7. HAA is further cleaved to 2-amino-3-carboxymuconic-6-semialdehyde by the action of HAA 3,4-dioxygenase. In this report we propose that ONB degradation occurs via the formation of HABA and the pathway branches at this point to form the two different aromatic intermediates AA and HAA by the action of a reductase and a mutase, respectively.

3-Hydroxyanthranilic Acid↗
PubMed2004

Purification, characterization, and gene cloning of cis,cis-muconate cycloisomerase from benzamide-assimilating Arthrobacter sp. BA-5-17.

cis,cis-Muconate cycloisomerase (MC) was purified to homogeneity from benzamide-assimilating Arthrobacter sp. BA-5-17. The purified enzyme showed high activities for cis,cis-muconate and 3-methyl-cis,cis-muconate, and preferred the 3-substituted derivatives over the derivatives with the same substituent at the 2 position as a substrate. A gene encoding MC of strain BA-5-17 was cloned and named catB. The catB gene was clustered with catR encoding a putative LysR-type regulator, catC encoding a putative muconolactone isomerase, and catA-II encoding the catechol 1,2-dioxygenase isozymes CD-III-1 and III-2. These genes showed the same orientation in transcriptional direction and the organization of cloned genes was catRBCA-II. In the phylogenetic analysis of MCs and chloro-MCs, the BA-5-17 and Streptomyces setonii MCs formed a subfamily, clearly distinguished from those of other MCs.

Amino Acid Sequence↗
PubMed2000

Purification of recombinant hydantoinase and L-N-carbamoylase from Arthrobacter aurescens expressed in Escherichia coli: comparison of wild-type and genetically modified proteins.

Two enzymes, hydantoinase (HyuH) and L-N-carbamoylase (HyuC), are required for the biocatalytic production of natural and unnatural, optically pure L-amino acids starting from D,L-5-monosubstituted hydantoins using the so called 'hydantoinase-method'. For the preparation of immobilized enzymes, which omit several drawbacks of whole cell biocatalysts, purified or at least enriched HyuH and HyuC have to be provided. In order to simplify existing purification protocols several genetically modified derivatives of HyuH and HyuC from Arthrobacter aurescens DSM 3747 have been cloned and expressed in E. coli. A fusion protein consisting of maltose-binding protein (MalE) and HyuH resulted in an enhanced solubility of the hydantoinase, which easily forms inclusion bodies. On the other hand the fusion protein could easily be purified with high yield (76%) by just one chromatographic step (amylose resin) and the complex purification protocol of the wild-type enzyme could therefore be simplified and shortened significantly. Interestingly, the specific activity of the MalE-HyuH fusion protein was as high as the wild-type enzyme despite that the molecular mass was doubled. A second modification of HyuH carrying a histidine-tag was efficiently bound to a metal affinity matrix but inactivated completely during elution from the column at either low pH or in the presence of imidazole. In the case of HyuC, an aspartate-tag has been added to the biocatalyst to allow an integrated purification-immobilization procedure since this enzyme is immobilized efficiently only via its carboxylic groups. The diminished isoelectric point of the Asp-tagged HyuC resulted in a simplified purification procedure. Compared to the wild-type enzyme expressed in E. coli HyuC-Asp6 was shifted off the elution range of the contaminating proteins and higher purification factors were obtained even in the capturing step. In contrast to HyuH, it was possible to purify a L-N-carbamoylase carrying a histidine-tag to apparent homogeneity using immobilized metal affinity chromatography. Therefore, the existing three step purification protocol was reduced to one chromatographic step and the yield of this relatively unstable protein enhanced remarkably.

Amidohydrolases↗
PubMed1998

Arthrobacter, Brachybacterium and Planococcus isolates identified from antarctic sea ice brine. Description of Planococcus mcmeekinii, sp. nov.

Three facultative psychrophilic Gram-positive bacterial strains were isolated from brine samples from the sea ice community in Antarctica. All strains were coccoid to rod-shaped and exhibited broad salinity and temperature ranges for growth. The three strains were subjected to 16S rDNA sequencing and subsequent phylogenetic analysis. All possess unique 16S rDNA sequences indicating they are new, previously unreported organisms. Phylogenetic analyses coupled with phenotypic characterization indicated that one of the strains is most closely related to the low mol% G + C genus Planococcus for which a new species, P. mcmeekinii, is proposed. The two other strains are members of the high mol% G + C Gram-positive bacteria and most closely related to the genera Arthrobacter and Brachybacterium. This study reports the first phylogenetic evidence that Gram-positive bacteria reside in the marine sea ice brine.

Actinomycetales↗
PubMed1998

Purification and characterization of four catechol 1,2-dioxygenase isozymes from the benzamide-assimilating bacterium Arthrobacter species BA-5-17.

When Arthrobacter sp. BA-5-17 was grown on benzamide, the bacterium synthesized four different catechol 1,2-dioxygenase (CD, EC 1.13.11.1) isozymes (CD-I, II, III-1, and III-2). We purified each CD to homogeneity by a series of column chromatography. The molecular masses of the four CDs were between 68 and 72 kDa. The enzymes were made up of two identical subunits each with the molecular mass of 33 kDa. CD-I and II were indistinguishable in enzymatic properties tested. Most properties of CD-III-1 were similar to those of CD-III-2. However, CD-III-1 had a marked adsorption peak at 325 nm, which disappeared in CD-III-2 as well as in CD-I and II. CD-III-1 and III-2 were much more resistant to heating and inhibitors than CD-I and II.

Amino Acid Sequence↗
PubMed2001

Purification and characterisation of an ester hydrolase from a strain of Arthrobacter species: its application in asymmetrisation of 2-benzyl-1,3-propanediol acylates.

An ester hydrolase (ABL) has been isolated from a strain of Arthrobacter species (RRLJ-1/95) maintained in the culture collection of this laboratory. The purified enzyme has a specific activity of 1700 U/mg protein and is found to be composed of a single subunit (Mr 32,000), exhibiting both lipase and esterase activities shown by hydrolysis of triglycerides and p-nitrophenyl acetate respectively. Potential application of the enzyme concerns the asymmetrisation of prochiral 2-benzyl-1,3-propanediol esters besides enantioselective hydrolysis of alkyl esters of unsubstituted and substituted 1-phenyl ethanols.

Arthrobacter↗
PubMed1989

13C, 15N, and 31P NMR studies on 6-hydroxy-L-nicotine oxidase from Arthrobacter oxidans.

The interaction between the apoprotein of 6-hydroxy-L-nicotine oxidase from Arthrobacter oxidans and the prosthetic group FAD has been investigated by 13C, 15N, and 31P NMR techniques. The FAD prosthetic group was selectively enriched in 13C and 15N isotopes by adding isotopically labeled riboflavin derivatives to the growth medium of riboflavin-requiring mutant cells. In the oxidized state the chemical shift of the C(7) and C(8) atoms indicates that the xylene moiety of the isoalloxazine ring is embedded in a hydrophobic environment. The polarization of the isoalloxazine ring as a whole is, however, much more comparable to that of free flavin in a polar and protic environment than to free flavin in an apolar environment. The polarization of the ring system can be ascribed to strong hydrogen bonds between the apoprotein and the two carbonyl groups. The binding of the competitive inhibitor, 6-hydroxy-D-nicotine, influences the resonances of the C(4a) and the N(5) atoms strongly. It is suggested that these shifts are due to a strong hydrogen-bonding interaction between the N(5) atom and the inhibitor. On reduction all resonances, except those of the C(10a) and the N(1) atoms, shift upfield, indicating the increased electron density in the ring system. In the dithionite-reduced enzyme, the ring system is bent at the N(5) position. Due to the bending of the N(5) atom and the sp2 hybridized N(10) atom, electron density from the N(10) atom is reallocated at the C(4) carbonyl group. In contrast, in the substrate-reduced enzyme the N(5) atom is almost completely sp2 hybridized, yielding a rather planar isoalloxazine ring.(ABSTRACT TRUNCATED AT 250 WORDS)

Arthrobacter↗
PubMed1976

Arthrobacter luteus restriction endonuclease recognition sequence and its cleavage map of SV40 DNA.

The nucleotide sequence at the cleavage site of the restriction endonuclease isolated from Arthrobacter luteus (Alu) has been determined. The endonuclease cleaves at the center of a palindromic tetranucleotide sequence to give even-ended duplex DNA fragments phosphorylated at the 5'-end. The endonuclease cleaves SV40 form I DNA into 32 fragments. The order and sizes of these fragments have been determined to provide an Alu cleavage map of the SV40 genome.

Arthrobacter↗
PubMed2002

Mechanistic aspects of the covalent flavoprotein dimethylglycine oxidase of Arthrobacter globiformis studied by stopped-flow spectrophotometry.

Dimethylglycine oxidase (DMGO) is a covalent flavoenzyme from Arthrobacter globiformis that catalyzes the oxidative demethylation of dimethylglycine to yield sarcosine, formaldehyde, and hydrogen peroxide. Stopped-flow and steady-state kinetic studies have been used to study the reductive and oxidative half-reactions using dimethylglycine and O2 as substrates. The reductive half-reaction is triphasic. The rate of the fast phase is dependent on substrate concentration, involves flavin reduction, and has a limiting rate constant of 244 s(-1). This phase also displays a kinetic isotope effect of 2.9. Completion of the first kinetic phase generates an intermediate with broad spectral signature between 350 and 500 nm, which is attributed to a reduced enzyme-iminium charge-transfer species, similar to the purple intermediate that accumulates in reactions of D-amino acid oxidase (DAAO) with alanine. The second phase (16 s(-1)) is independent of substrate concentration and is attributed to iminium hydrolysis/deprotonation. The third phase (2 s(-1)) is attributed to product release, the rate of which is less than the steady-state turnover rate (10.6 s(-1)). Flavin oxidation of dithionite- and dimethylglycine-reduced enzyme by O2 occurs in a single phase, and the rate shows a linear dependence on oxygen concentration, giving bimolecular rate constants of 342 and 201 mM(-1) x s(-1), respectively. Enzyme-monitored turnover experiments indicate that decay of the reduced enzyme-iminium intermediate is rate-limiting, consistent with rate constants determined from single turnover studies. A minimal kinetic mechanism is presented, which establishes a close relationship to the mechanism of action of DAAO. The covalent flavin in dimethylglycine oxidase is identified as an alphaN1-histidyl48-FAD, and equilibrium titration studies establish a single redox center that displays typical flavoprotein 'oxidase' characteristics.

Arthrobacter↗
PubMed2003

Structural characterization and mapping of the covalently linked FAD cofactor in choline oxidase from Arthrobacter globiformis.

The flavoenzyme choline oxidase catalyzes the oxidation of choline and betaine aldehyde to betaine. Earlier studies have shown that the choline oxidase from Arthrobacter globiformis contains FAD covalently linked to a histidine residue. To identify the exact type of flavin binding, the FAD-carrying amino acid residue was released by acid hydrolysis. The fluorescence excitation maxima of the isolated aminoacylriboflavin, showing a hypsochromic shift of the near-ultraviolet band relative to riboflavin, and the pH-dependent flavin fluorescence confirmed the presence of an 8alpha-substituted flavin linked to histidine. Similarly, MALDI-TOF mass spectrometry showed a molecular mass corresponding to histidylriboflavin. Classical experiments used to distinguish between the N(1) and N(3) isomers all indicated that the flavin was linked to the N(1) position of the histidine residue. The position of the FAD-carrying histidine residue in the choline oxidase polypeptide was identified by tryptic cleavage of the denatured enzyme, HPLC separation of the proteolytic peptide fragments, and characterization of the purified flavin-carrying peptide by mass spectrometry and spectroscopy. The FAD moiety was assigned to the tryptic peptide, His-Ala-Arg, corresponding to residues 87-89 in the open reading frame of the previously published cDNA sequence. Further analysis of the flavopeptide by collision-induced dissociation mass spectrometry confirmed that the flavin cofactor was attached to His(87). We conclude that this variant of choline oxidase contains 8alpha-[N(1)-histidyl]FAD at position 87 in the polypeptide chain.

Alcohol Oxidoreductases↗
PubMed2006

Mechanism of FAD reduction and role of active site residues His-225 and Tyr-259 in Arthrobacter globiformis dimethylglycine oxidase: analysis of mutant structure and catalytic function.

Residues His-225 and Tyr-259 are located close to the FAD in the dehydrogenase active site of the bifunctional dimethylglycine oxidase (DMGO) of Arthrobacter globiformis. We have suggested [Leys, D., Basran, J., and Scrutton, N. S. (2003) EMBO J. 22, 4038-4048] that these residues are involved in abstraction of a proton from the substrate amine group of dimethylglycine prior to C-H bond breakage and FAD reduction. To investigate this proposal, we have isolated two mutant forms of DMGO in which (i) His-225 is replaced with Gln-225 (H225Q mutant) and (ii) Tyr-259 is replaced with Phe-259 (Y259F mutant). Both mutant enzymes retain the ability to oxidize substrate, but the steady-state turnover of the Y259F mutant is attenuated more than 200-fold. Only modest changes in kinetic parameters are observed for the H225Q mutant during steady-state turnover. Stopped-flow studies indicate that the rate of FAD reduction in the Y259F enzyme is substantially impaired by a factor of approximately 1500 compared with that of the wild-type enzyme, suggesting a key role for this residue in the reductive half-reaction of the enzyme. The kinetics of FAD reduction in the H225Q enzyme are complex and involve three discrete kinetic phases that are attributed to different conformational states of this mutant, evidence for which is provided by crystallographic analysis. Neither the H225Q enzyme nor the Y259F enzyme stabilizes the FADH(2)-iminium charge-transfer complex observed previously in stopped-flow studies with the wild-type enzyme. Our studies are consistent with a key role for Tyr-259, but not His-225, in deprotonation of the substrate amine group prior to FAD reduction. We infer that residue His-225 is likely to modulate the acid-base properties of Tyr-259 by perturbing the pK(a) of Tyr-259 and thus fine-tunes the reaction chemistry to facilitate proton abstraction under physiological conditions. Our data are discussed in the context of the crystallographic data for DMGO and also in relation to contemporary mechanisms for flavoprotein-catalyzed oxidation of amine substrates.

Arthrobacter↗
PubMed1996

Manganese(II)-dependent extradiol-cleaving catechol dioxygenase from Arthrobacter globiformis CM-2.

A manganese-dependent 3,4-dihydroxyphenylactate 2,3-dioxygenase from Arthrobacter globiformis strain CM-2 (MndD) cloned in Escherichia coli has been purified to homogeneity. Sedimentation equilibrium analysis indicates an alpha 4 homotetrameric holoenzyme structure (4 x 38,861 Da). Steady-state kinetic analysis of MndD with a variety of substrates and inhibitors yields very similar relative rates to the known Fe(II)- and Mn(II)-dependent 3,4-dihydroxyphenylacetate 2,3-dioxygenases from Pseudomonas ovalis and Bacillus brevis, respectively. Yet, unlike the Fe(II)-dependent enzyme, MndD retains almost all activity in the presence of H2O2 and CN- and is inactivated by Fe(II). ICP emission analysis confirms the presence of 3.0 +/- 0.2 g-atoms Mn (and only 0.7 +/- 0.2 g-atoms Fe) per tetrameric holoenzyme molecule. Comparison of MndD samples with varying metal content, including an apo and partial-apo enzyme preparation, shows a strong positive correlation between specific activity and Mn content. EPR spectra of MndD as isolated exhibit a nearly isotropic g = 2.0 signal having 6-fold hyperfine splitting (A = 95 G) typical of octahedrally coordinated Mn(II) in a protein. Quantitation of the EPR spin yields 3.4 +/- 0.3 g-atoms of Mn(II) per holoenzyme. When exposed anaerobically to its natural substrate, 3,4-dihydroxyphenylacetate (3,4-DHPA), the EPR spectrum undergoes a dramatic change characterized by the attenuation of the g = 2 signal and the appearance of new signals at g = 1.2, 2.9, 4.3, and 16. The g = 4.3 signal displays 6-fold hyperfine splitting (A = 95 G) that unambiguously assigns it to the Mn(II) center. The appearance of these new signals indicates a large increase in zero-field splitting suggestive of a change in ligand coordination to the Mn(II) center. Similarly perturbed signals are seen in the EPR spectra of MndD complexed with the comparably active substrate analog, D,L-3,4-dihydroxymandelate, or the tight-binding inhibitor, p-nitrocatechol, but not in the complexes with weaker binding substrates and inhibitors. The fact that only strong-binding substrates and inhibitors significantly perturb the Mn(II) EPR signal strongly suggests that the substrate coordinates to the Mn(II) center in the catalytic pathway.

Arthrobacter↗
PubMed1997

Manganese(II) active site mutants of 3,4-dihydroxyphenylacetate 2,3-dioxygenase from Arthrobacter globiformis strain CM-2.

Whereas all other members of the extradiol-cleaving catechol dioxygenase family are iron-dependent, the 3,4-dihydroxyphenylacetate 2,3-dioxygenase (MndD) from Arthrobacter globiformis CM-2 is dependent on manganese for catalytic activity. Recently, the endogenous iron ligands of one family member, the 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC), were identified crystallographically as two histidines and a glutamic acid [Sugiyama, K., et al. (1995) Proc. Jpn. Acad., Ser. B 71, 32-35; Han, et al. (1995) Science 270, 976-980; Senda, T., et al. (1996) J. Mol. Biol. 255, 735-752]. Though BphC and MndD have low overall sequence identity (23%), the three BphC metal ligands are all conserved in MndD (H155, H214, and E266). In order to determine whether these residues also act as ligands to manganese in MndD, site-directed mutants of each were constructed, purified, and analyzed for activity and metal content. Mutations H155A, H214A, and E266Q yielded purified enzymes with specific activities of <0.1% of that of the wild-type dioxygenase and bound 0.4, 1.8, and 33% of the wild-type level of manganese, respectively. The relatively high level of manganese [with a Mn(II) EPR signal distinctly different from that of the wild-type enzyme] observed for E266Q suggests that the glutamine may act as a weak ligand to the metal. Mutant E266D, which retains the potential metal binding capability of a carboxylate group, exhibited 12% of the wild-type activity in crude extracts, suggesting that Mn remains bound; however, this mutant protein was too unstable to be purified and analyzed for metal content. On the basis of the low activity and metal content of mutant proteins, we propose that the conserved residues H155, H214, and E266 ligate manganese in MndD. As is the case with the superoxide dismutases, the extradiol-cleaving catechol dioxygenases appear to utilize identical coordinating residues for their iron- and manganese-dependent enzymes.

Amino Acid Sequence↗
PubMed1997

Crystal structures of the copper-containing amine oxidase from Arthrobacter globiformis in the holo and apo forms: implications for the biogenesis of topaquinone.

The crystal structures of the copper enzyme phenylethylamine oxidase from the Gram-positive bacterium Arthrobacter globiformis (AGAO) have been determined and refined for three forms of the enzyme: the holoenzyme in its active form (at 2.2 A resolution), the holoenzyme in an inactive form (at 2.8 A resolution), and the apoenzyme (at 2.2 A resolution). The holoenzyme has a topaquinone (TPQ) cofactor formed from the apoenzyme by the post-translational modification of a tyrosine residue in the presence of Cu2+. Significant differences between the three forms of AGAO are limited to the active site. The polypeptide fold is closely similar to those of the amine oxidases from Escherichia coli [Parsons, M. R., et al. (1995) Structure 3, 1171-1184] and pea seedlings [Kumar, V., et al. (1996) Structure 4, 943-955]. In the active form of holo-AGAO, the active-site Cu atom is coordinated by three His residues and two water molecules in an approximately square-pyramidal arrangement. In the inactive form, the Cu atom is coordinated by the same three His residues and by the phenolic oxygen of the TPQ, the geometry being quasi-trigonal-pyramidal. There is evidence of disorder in the crystals of both forms of holo-AGAO. As a result, only the position of the aromatic group of the TPQ cofactor, but not its orientation about the Cbeta-Cgamma bond, is determined unequivocally. In apo-AGAO, electron density consistent with an unmodified Tyr occurs at a position close to that of the TPQ in the inactive holo-AGAO. This observation has implications for the biogenesis of TPQ. Two features which have not been described previously in amine oxidase structures are a channel from the molecular surface to the active site and a solvent-filled cavity at the major interface between the two subunits of the dimer.

Amine Oxidase (Copper-Containing)↗
PubMedDate not supplied

Immobilization of Arthrobacter simplex in thermally reversible hydrogels: effect of gel hydrophobicity on steroid conversion.

Arthrobacter simplex cells have been immobilized in a series of thermally reversible hydrogels having different gel hydrophobicities. Steroid conversion from hydrocortisone to prednisolone via the delta 1-dehydrogenase system was greatly affected by the relative hydrophobicities of the gel matrices, which were prepared by copolymerizing varying ratios of N-isopropylacrylamide to acrylamide. The characteristics of the immobilized cells, such as optimal temperatures, Km values, and the effects of an added artificial electron acceptor, were largely influenced by the gel matrices and their different lower critical solution temperatures (LCST). The data indicate that the microenvironment of the dehydrogenation system is quite different within the different hydrophilic/hydrophobic gel matrices. The high partitioning of water-insoluble steroids into the hydrophobic regions and the reduced possibility of product inhibition within the more hydrophobic gel matrices may cause the observed higher steroid conversion in these gels. A possible model for immobilized A. simplex cells in such different gel matrices is proposed.

Acrylamides↗
PubMedDate not supplied

Biotreatment of ammonia from air by an immobilized Arthrobacter oxydans CH8 biofilter.

A heterotrophic Arthrobacter oxydans CH8 that was capable of removing NH3 from NH3 containing gas was isolated from livestock farming wastewater. The A. oxydans CH8 was immobilized with calcium alginate packed into filter column. Metered NH3-containing gas was partially humidified and passed through the glass column. Extensive tests including the removal characteristics, the removal efficiencies, and the metabolic products of NH3 by A. oxydans CH8 were conducted. Additionally, the operation criteria for the biofilter was also established. NH3 removel capacities were elevated by the immobilized-cell (biological conversion) method and the BDST (bed depth service time) method (physical adsorption), respectively. The optium temperature for removing NH3 was 30 degrees C, while the nitrification ability remained 80% at 40 degrees C. The high efficiency (> 97%) in the removal of NH3 was attained at 36 L/h with pH control and was not decreased because of high NH3 inlet concentration. In addition, the high maximum removal rate (1.22 g of N/day (kg of bead)) enhanced the use of the biofilter in industrial-scale NH3(g) pollution control. The ability to remove NH3 at high inlet concentration and temperature suggested that the immobilized A. oxydans CH8 biofilter has potential in processing NH3 gas.

Adsorption↗