Post-embryonic development of circadian rhythm in the cricket,Gryllus bimaculatus: A rhythm reversal

Summary Locomotor activity of the male cricketGryllus bimaculatus DeGeer was recorded from the 7th or last (8th) instar nymph. The nymph showed a diurnal rhythm (nymphal rhythm = NR), while the adult, on the contrary, was nocturnal (adult rhythm = AR) (Fig. 1). This rhythm reversal occurred suddenly 3 to 5 days after the imaginal molt, almost simultaneously with the first spermatophore formation and the start of stridulation (calling song) (Fig. 2). In addition to the antiphase relationship, both rhythms also differed in the freerunning period (tau) and wave form. Tau_scdd was significantly longer in NR (24.33 h) than in AR (23.91 h) (Fig. 3). AR was characterized by a sharp activity peak in each cycle, which NR, however, lacked (Fig. 1, 3, 6). On the basis of these differences, two possibilities are discussed; one is that NR and AR are separate oscillations and the other is that both are coupled to different phase points of one oscillation.Abbreviations LD light dark - DD constant darkness - LL constant light - NR nymphal rhythm - AR adult rhythm     

High activity catechol 2,3-dioxygenase from the cresols - Degrading Stenotrophomonas maltophilia strain KB2

This study aimed at characterization of catechol 2,3-dioxygenase from Stenotrophomonas maltophilia KB2, being able to utilize a wide spectrum of aromatic substrates as a sole carbon and energy source. 2-methylphenol, 3-methylphenol, and 4-methylphenol was completely degraded during 24 h in concentration 6 mM, 7 mM, and 5 mM, respectively. When cells of strain KB2 were growing on methylphenols, catechol 2,3-dioxygenase was induced. Biochemical analysis revealed that the examined enzyme was similar to another catechol 2,3-dioxygenases, but showed extremely high activity. The enzyme was optimally active at 30 °C and pH 7.6. Kinetic studies showed that the value of K_m, V_max and Hill constant was 85.11 ??M, 3.08 ??M min⁻¹ and 4.09 respectively. Comparative structural and phylogenetic analysis of catechol 2,3-dioxygenase from S. maltophilia KB2 had placed the protein with the single-ring substrate subfamily of the extradiol dioxygenase. We observed the presence of externally located ??-helices and internally located ??-sheets. We also suggest that the Fe²⁺ ion binding is facilitated via four ligands: two histidine residues, one glutamate residue and one molecule of water.     

Cyclic 2,3-diphosphoglycerate metabolism in Methanobacterium thermoautotrophicum (strain ΔH): characterization of the synthetase reaction

The levels of cyclic 2,3-diphosphoglycerate (cDPG) in methanogenic bacteria are governed by the antagonistic activities of cDPG synthetase and cDPG hydrolase. In this paper we focus on the synthetase from Methanobacterium thermoautotrophicum. The cytoplasmic 150 kDa enzyme catalyzed cDPG synthesis from 2,3-diphosphoglycerate (apparent K_m=21 mM), Mg²⁺ (K_m=3.1 mM) and ATP (K_m=1–2 mM). In batch-fed cultures, the enzyme was constitutively present (6–6.5 nmol per min per mg protein) during the different growth phases. In continuous cultures, activity decreased in response to phosphate limitation. The synthetase reaction proceeded with maximal rate at pH 6 and at 65° C and was specifically dependent on high (>0.3M) K⁺ concentrations. The reaction conditions remarkably contrasted to those of cDPG degradation catalyzed by the previously described membrane-bound cDPG hydrolase.Abbreviations cDPG Cyclic 2,3-diphosphoglycerate - 2,3-DPG 2,3-Diphosphoglycerate - 2-PG 2-Phosphoglycerate - 3-PG 3-Phosphoglycerate     

Biochemical characterization of L-DOPA 2,3-dioxygenase, a single-domain type I extradiol dioxygenase from lincomycin biosynthesis

l-DOPA-2,3-dioxygenase from Streptomyces lincolnensis is a single-domain type I extradiol dioxygenase of the vicinal oxygen chelate superfamily and catalyzes the second step in the metabolism of tyrosine to the propylhygric acid moiety of the antibiotic, lincomycin. S. lincolnensisl-DOPA-2,3-dioxygenase was overexpressed, purified and reconstituted with Fe(II). The activity of l-DOPA-2,3-dioxygenase was kinetically characterized with l-DOPA (K_M = 38 μM, k_cat = 4.2 min⁻¹) and additional catecholic substrates including dopamine, 3,4-dihydroxyhydrocinnamic acid, catechol and d-DOPA. 3,4-Dihydroxyphenylacetic acid was characterized as a competitive inhibitor of the enzyme (K_i = 2.2 mM). Site-directed mutagenesis and its effects on enzymatic activity were used to identify His14 and His70 as iron ligands.     

Kynurenine Pathway Enzymes in Brain: Responses to Ischemic Brain Injury Versus Systemic Immune Activation

Accumulation of l -kynurenine and quinolinic acid (QUIN) in the brain occurs after either ischemic brain injury or after systemic administration of pokeweed mitogen. Although conversion of l -[¹³C₆]tryptophan to [¹³C₆]-QUIN has not been demonstrated in brain either from normal gerbils or from gerbils given pokeweed mitogen, direct conversion in brain tissue does occur 4 days after transient cerebral ischemia. Increased activities of enzymes distal to indoleamine-2,3-dioxygenase may determine whether l -kynurenine is converted to QUIN. One day after 10 min of cerebral ischemia, the activities of kynureninase and 3-hydroxy-3,4-dioxygenase were increased in the hippocampus, but local QUIN levels and the activities of the indoleamine-2,3-dioxygenase and kynurenine-3-hydroxylase were unchanged. By days 2 and 4 after ischemia, however, the activities of all of these enzymes in the hippocampus as well as QUIN levels were significantly increased. Kynurenine aminotransferase activity in the hippocampus was unchanged on days 1 and 2 after ischemia but was decreased on day 4, at a time when local kynurenic acid levels were unchanged. A putative precursor of QUIN, [¹³C₆]anthranilic acid, was not converted to [¹³C₆]-QUIN in the hippocampus of either normal or 4-day postischemic gerbils. Gerbil macrophages stimulated by endo-toxin in vitro converted l -[¹³C₆]tryptophan to [¹³C_e]QUIN. Kinetic analysis of kynurenine-3-hydroxylase activity in the cerebral cortex of postischemic gerbils showed that V_max increased, without changes in K_m. Systemic administration of pokeweed mitogen increased indoleamine-2,3-dioxygenase and kynureninase activities in the brain without significant changes in kynurenine-3-hydroxylase or 3-hydroxyanthranilate-3,4-dioxygenase activities. Increases in kynurenine-3-hydroxylase activity, in conjunction with induction of indoleamine-2,3-dioxygenase, kynureninase, and 3-hydroxyanthranilate-3,4-dioxygenase in macro-phage infiltrates at the site of brain injury, may explain the ability of postischemic hippocampus to convert l -[¹³C₆]tryptophan to [¹³C₆]QUIN.     

Inactivation of 2,3-dihydroxybiphenyl 1,2-dioxygenase fromPseudomonas sp. strain CB406 by 3,4-dihydroxybiphenyl (4-phenylcatechol)

Summary 3,4-dihydroxybiphenyl is not a substrate for the 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC) from biphenyldegradingPseudomonas sp. strain CB406. It acts as both a reversible inhibitor and a potent inactivator of the enzyme. The inactivation process requires the presence of O₂ and can be reversed by the removal of the 3,4-dihydroxybiphenyl followed by incubation of the enzyme in the presence of dithioerythritol and Fe²⁺ under anaerobic conditions. Two other extradiol dioxygenases behave similarly, the catechol 2,3-dioxygenase (BphE) from strain CB406 and the BphC fromPseudomonas sp. strain LB400. The BphC fromP. testosteroni B-356 also did not cleave 3,4-dihydroxybiphenyl but it was not inactivated.Abbreviations C23o Catechol 2,3-dioxygenase - 34DHBP 3,4-dihydroxybiphenyl     

Expression and homology modeling of 2′-aminobiphenyl-2,3-diol-1,2-dioxygenase from Pseudomonas stutzeri carbazole degradation pathway

The enzyme 2′-aminobiphenyl-2,3-diol-1,2-dioxygenase (CarB), encoded by two genes (carBa and carBb), is an α₂β₂ heterotetramer that presents meta-cleavage activity toward the hydroxylated aromatic ring in the carbazole degradation pathway from petroleum-degrader bacteria Pseudomonas spp. The 1082-base, pair polymerase chain reaction product corresponding to, carBaBb genes from Pseudomonas stutzeri ATCC 31258 was cloned by site-specific recombination and expressed in high levels in Escherichia coli BL21-SI with a histidine-tag and in native form. The CarB activity toward 2,3-dihydroxybiphenyl was similar for these two constructions. The α₂β₂ 3D model of CarB dioxygenase was proposed by homology modeling using the protocatechuate 4,5-dioxygenase (LigAB) structure as template. Accordingly, His12, His53, and Glu230 coordinate the Fe(II) in the catalytic site at the subunit CarBb. The model also indicates that His182 is the catalytic base responsible for deprotonating one of the hydroxyl group of the substrate by a hydrogen bond. The hydrophobic residues Trp257 and Phe258 in the CarB structure substituted the LigAB amino acid residues Ser269 and Asn270. These data could explain why the CarB was active for 2,3-dihydroxybiphenyl and not for protocatechuate.     

Changes in nuclear electrolytes of Chironomus thummi salivary gland cells during development

A technique is described for the measurement of Na⁺, K⁺ and Mg²⁺ in cytoplasmic samples and nuclei from chironomid salivary glands. [Na], [K] and [Mg] were followed from the penultimate (L₃) through the last larval instar (L₄) until pupation, in the two developmental types, R and B, of Chironomus thummi. In nuclei, [Mg] falls from 78 mM in the middle of the L₃ to about 27 mM at the L₃ → L₄ molt, a level which is maintained thereafter. [Na] falls from 180 mM to around 60 mM at the L₃ → L₄ molt and falls further to about 38 mM in the prepupa; the pattern of change differs between the developmental types. [K] increases at both molts, from a level of 131 mM to about 150 mM at the L₃ → L₄ molt and from about 115 mM to about 130 mM at the pupal molt, the developmental types differing again. The cytoplasmic ion content measured during the prepupal stage runs parallel to the nuclear samples but always contains about 18 mM more Na and 12 mM less K than the nuclei. In the nuclei the ∑[Na + K] has a steady downward trend but rises slightly in the prepupa. The Na/K ratio follows a complex course related to the molt cycles. Analysis of variation allows to discern subclasses of nuclei with a particularly high Na/K ratio; the frequency of such nuclei is followed through development. It is argued (a) that the observed alterations in cation composition are of a kind and magnitude which under experimental conditions can induce puffs in certain chromosomal segments, and (b) that shifts in ion concentration may be implicated in the control of DNA replication.     

Catechol 1,2-dioxygenase from α-naphthol degrading thermophilic Geobacillus sp. strain: purification and properties

The purpose of this study was purification and characterization of catechol 1,2-dioxygenase from Geobacillus sp. G27 strain, which degrades α-naphthol by the β-ketoadipate pathway. The catechol 1,2-dioxygenase (C1,2O) was purified using four steps of ammonium sulfate precipitation, DEAE-celullose, Sephadex G-150 and hydroxylapatite chromatographies. The enzyme was purified about 18-fold with a specific activity of 7.42 U mg of protein⁻¹. The relative molecular mass of the native enzyme estimated on gel chromatography of Sephadex G-150 was 96 kDa. The pH and temperature optima for enzyme activity were 7 and 60°C, respectively. A half-life of the catechol 1,2-dioxygenase at the optimum temperature was 40 min. The kinetic parameters of the Geobacillus sp. G27 strain catechol 1,2-dioxygenase were determined. The enzyme had apparent K_m of 29 μM for catechol and the cleavage activities for methylcatechols were much less than for catechol and no activity with gentisate or protocatechuate was detected.     

Degradation of diphenylether by Pseudomonas cepacia Et4: enzymatic release of phenol from 2,3-dihydroxydiphenylether

2,3-Dihydroxybiphenyl dioxygenase from Pseudomonas cepacia Et 4 was found to catalyze the ring fission of 2,3-dihydroxydiphenylether in the course of diphenylether degradation. The enzyme was purified and characterized. It had a molecular mass of 240 kDa and is dissociated by SDS into eight subunits of equal mass (31 kDa). The purified enzyme was found to be most active with 2,3-dihydroxybiphenyl as substrate and showed moderate activity with 2,3-dihydroxydiphenylether, catechol and some 3-substituted catechols. The K _m-value of 1 M for 2,3-dihydroxydiphenylether indicated a high affinity of the enzyme towards this substrate. The cleavage of 2,3-dihydroxydiphenylether by 2,3-dihydroxybiphenyl dioxygenase lead to the formation of phenol and 2-pyrone-6-carboxylate as products of ring fission and ether cleavage without participation of free intermediates. Isotope labeling experiments carried out with ¹⁸O₂ and H₂ ¹⁸O indicated the incorporation of ¹⁸O from the atmosphere into the carboxyl residue as well as into the carbonyl oxygen of the lactone moiety of 2-pyrone-6-carboxylate. Based on these experimental findings the reaction mechanism for the formation of phenol and 2-pyrone-6-carboxylate is proposed in accordance with the mechanism suggested by Kersten et al. (1982).Non-standard abbreviations DPE diphenylether - 2,3-dihydroxy-DPE 2,3-dihydroxydiphenylether - PCA 2-pyrone-6-carboxylic acid - 2,3-dihydroxy-BP dioxygenase 2,3-dihydroxybiphenyl dioxygenase - GC gas chromatography     

Isolation and characterization of four novel Gram-positive bacteria associated with the rhizosphere of two endemorelict plants capable of degrading a broad range of aromatic substrates

Four new Gram-positive, phenol-degrading strains were isolated from the rhizospheres of endemorelict plants Ramonda serbica and Ramonda nathaliae known to exude high amounts of phenolics in the soil. Isolates were designated Bacillus sp. PS1, Bacillus sp. PS11, Streptomyces sp. PS12, and Streptomyces sp. PN1 based on 16S rDNA sequence and biochemical analysis. In addition to their ability to tolerate and utilize high amounts of phenol of either up to 800 or up to 1,400 mg l⁻¹ without apparent inhibition in growth, all four strains were also able to degrade a broad range of aromatic substrates including benzene, toluene, ethylbenzene, xylenes, styrene, halogenated benzenes, and naphthalene. Isolates were able to grow in pure culture and in defined mixed culture on phenol and on the mixture of BTEX (benzene, toluene, ethylbenzene, and xylenes) compounds as a sole source of carbon and energy. Pure culture of Bacillus sp. PS11 yielded 1.5-fold higher biomass amounts in comparison to mixed culture, under all conditions. Strains successfully degraded phenol in the soil model system (2 g kg⁻¹) within 6 days. Activities of phenol hydroxylase, catechol 1,2-dioxygenase, and catechol 2,3-dioxygenase were detected and analyzed from the crude cell extract of the isolates. While all four strains use ortho degradation pathway, enzyme indicative of meta degradation pathway (catechol 2,3-dioxygenase) was also detected in Bacillus sp. PS11 and Streptomyces sp. PN1. Phenol degradation activities were induced 2 h after supplementation by phenol, but not by catechol. Catechol slightly inhibited activity of catechol 2,3-dioxygenase in strains PS11 and PN1.     

Catechol 2,3-dioxygenase from the thermophilic, phenol-degrading Bacillus thermoleovorans strain A2 has unexpected low thermal stability

Catechol 2,3-dioxygenase from the thermophilic Bacillus thermoleovorans A2 was purified and characterized. The catechol 2,3-dioxygenase has a molecular mass of 135 000 Da and consists of four identical subunits of 34 700 Da. One iron per enzyme subunit was detected using atom absorption spectroscopy. Enzyme activity was not inhibited by EDTA, suggesting that the iron is tightly bound. Addition of hydrogen peroxide to the enzyme completely destroyed activity, indicating that the iron was in the divalent state. The isoelectric point of the enzyme was 4.8. The enzyme displayed optimal activity at pH 7.2 and 70°C. The half-life of the catechol 2,3-dioxygenase at the optimum temperature was 1.5 min under aerobic conditions and 10 min in a nitrogen atmosphere. This stability of the enzyme is comparable to the stability of the enzyme from the mesophilic Pseudomonas putida mt-2. The stability of the cloned enzyme in E. coli extracts was identical to the stability in wild-type extracts, suggesting that no stabilizing factors were present in Bacillus thermoleovorans A2 In whole cells the half-life of the enzyme at 70°C was approximately 26 min, when protein synthesis was disrupted by chloramphenicol; however, the activity remained constant when protein synthesis was not inhibited. From these results we concluded that catechol 2,3-dioxygenase from Bacillus thermoleovorans A2 is not particularly thermostable, but that the organism retains the ability to degrade phenol at high temperatures because of continuous production of this enzyme. Received: October 10, 1998 / Accepted: March 18, 1999     

Purification and partial characterization of the extradiol dioxygenase, 2′-carboxy-2,3-dihydroxybiphenyl 1,2-dioxygenase,in the fluorene degradation pathway from Rhodococcus sp. strain DFA3

Type II extradiol dioxygenase, 2′-carboxy-2,3-dihydroxybiphenyl 1,2-dioxygenase (FlnD1D2) involved in the fluorene degradation pathway of Rhodococcus sp. DFA3 was purified to homogeneity from a heterologously expressing Escherichia coli. Gel filtration chromatography and SDS-PAGE suggested that FlnD1D2 is an α₄β₄ heterooctamer and that the molecular masses of these subunits are 30 and 9.9 kDa, respectively. The optimum pH and temperature for enzyme activity were 8.0 and 30 °C, respectively. Assessment of metal ion effects suggested that exogenously supplied Fe²⁺ increases enzyme activity 3.2-fold. FlnD1D2 catalyzed meta-cleavage of 2′-carboxy-2,3-dihydroxybiphenyl homologous compounds, but not single-ring catecholic compounds. The K_m and k_cat/K_m values of FlnD1D2 for 2,3-dihidroxybiphenyl were 97.2 μM and 1.5 × 10^?2 μM^?1sec^?1, and for 2,2′,3-trihydroxybiphenyl, they were 168.0 μM and 0.5 × 10^?2 μM^?1sec^?1, respectively. A phylogenetic tree of the large and small subunits of type II extradiol dioxygenases suggested that FlnD1D2 constitutes a novel subgroup among heterooligomeric type II extradiol dioxygenases.     

Purification and characterization of juvenile hormone esterase from hemolymph of the Colorado potato beetle

In the Colorado potato beetle (Leptinotarsa decemlineata), low juvenile hormone (JH) titers are necessary to initiate metamorphosis and diapause. Low JH titers coincide with high activities of JH esterase, which occur mainly in the hemolymph. The specific activity of JH esterase appeared to be highest in the last larval instar, at day 3 after the molt, and reached a value of 13.5 nmol/min/mg. JH esterase was purified from hemolymph collected at this stage by a sequence of separation systems, including preparative nondenaturing PAGE, isoelectric focusing, and SDS-PAGE. The enzyme had a molecular weight of 120,000 and was composed of two subunits with molecular weights of 57,000, which were not linked by disulphide bridges. Isoelectric focusing revealed two forms of the enzyme with isoelectric points of 5.5 and 5.6. The K_m and k_cat of the purified enzyme were determined. The major form with pI 5.6 had a K_m of 1.4 × 10^-6M and a k_cat of 0.9 s^-1 and the minor form with pI 5.5 had a K_m of 2.2 × 10^-6M and a k_cat of 1.9 s^-1. The quaternary structure of L. decemlineata JH esterase as a dimer, differs from JH esterases in other species, which are monomers. Arch. Insect Biochem. Physiol. 35:261-277, 1997.© 1997 Wiley-Liss, Inc.     

Energetics for activity in the salamanderAmphiuma tridactylum

Summary Various metabolic parameters were measured in relation to activity in the salamanderAmphiuma tridactylum. Cutaneous O₂ consumption rate ( ) did not change with activity (Fig. 1B). Pulmonary did not increase during activity, but did increase after activity, repaying the O₂ debt (Fig. 1). Changes in lactate, glycogen and glucose indicated that: 1) the energy for activity is primarily derived from oxidation of muscle glycogen to lactate; 2) gluconeogenesis reaches a peak at 5 h after activity; and 3) total replenishment of muscle lactate may not occur until after the animal feeds again (Figs. 2,3). The measured O₂ debt of activity was 266.47 l g^–1 (Fig. 1B). The amount of excess lactate generated (1.52 mg g^–1), estimates of O₂ stores, and estimates of high energy phosphate stores were used to calculate an O₂ debt (265.61 l g^–1) which agreed with the measured O₂ debt (Fig. 4); 76% is a lactacid and 24% is an alactacid debt. The total energy cost of activity was calculated from similar estimates (Fig. 5). It is suggested thatAmphiuma can remain active longer than other amphibians which have similar anaerobic capacities because of the efficiency of swimming as a means of locomotion. The results are used in interpreting evolution of the lungs ofAmphiuma.     

Zur Glykolatoxydation einzelliger Grünalgen

Summary O₂-uptake and CO₂-release by a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris increase on addition of Na-glycolate by factors of 4–5 and 5–6, respectively (Fig. 1). In an enzyme preparation of that alga (sonification, centrifugation, precipitation with 0–30% (NH₄)₂SO₄, dialysis) activity of glycolate oxidase can be demonstrated by O₂-uptake (Fig. 2a) as well as by reduction of the artificial electron acceptor DCPIP (Fig. 2b). The same holds true for whole cells as well as equally prepared enzyme preparations of heterotrophically or autotrophically grown wildtype Chlorella vulgaris, provided the cells are cracked by a French press instead of a sonicator (Figs. 3a-c and 4a-c). Glyoxylate is the main reaction product (Table). Oxidation of exogenous glycolate is rapidly performed by whole cells of Scenedesmus quadricauda and of Ankistrodesmus convolutus, too, but hardly or not at all by Chlorella pyrenoidosa and Ankistrodesmus braunii. No definite influence of the level of CO₂ applied during growth is found: Chlorella vulgaris and Ankistrodesmus convolutus show a rapid oxidation of glycolate after growth under 0,03 and 1,5% CO₂ in air, whereas Chlorella pyrenoidosa and Ankistrodesmus braunii do not show an enhanced O₂-uptake on addition of glycolate after either condition (Fig. 5). Various developmental stages of Chlorella pyrenoidosa respond differently to addition of glycolate, the extra O₂-consumption varying between about 25% (mature cells) and 50–60% (young cells) of the endogenous rate (Fig. 6). It thus appears that species of unicellular green algae within the same genus have strong or weak glycolate oxidase activity and that several external factors have only a modifying effect on that enzyme.     

Catechol 1,2-dioxygenase from the new aromatic compounds - Degrading Pseudomonas putida strain N6

This study aimed to characterization of catechol 1,2-dioxygenase from a Gram-negative bacterium, being able to utilize a wide spectrum of aromatic substrates as a sole carbon and energy source. Strain designated as N6, was isolated from the activated sludge samples of a sewage treatment plant at Bentwood Furniture Factory Jasienica, Poland. Morphology, physio-biochemical characteristics and phylogenetic analysis based on 16S rDNA sequence indicate that strain belongs to Pseudomonas putida. When cells of strain N6 grown on protocatechuate or 4-hydroxybenzoic acid mainly protocatechuate 3,4-dioxygenase was induced. The activity of catechol 1,2-dioxygenase was rather small. The cells grown on benzoic acid, catechol or phenol showed high activity of only catechol 1,2-dioxygenase. This enzyme was optimally active at 35 °C and pH 7.4. Kinetic studies showed that the value of K_m and V_max was 85.19 ??M and 14.54 ??M min⁻¹ respectively. Nucleotide sequence of gene encoding catechol 1,2-dioxygenase in strain N6 has 100% identity with catA genes from two P. putida strains. The deduced 301-residue sequence of enzyme corresponds to a protein of molecular mass 33.1 kDa. The deduced molecular structure of the catechol 1,2-dioxygenase from P. putida N6 was very similar and characteristic for the other intradiol dioxygenases.     

Inhibition of indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase by β-carboline and indole derivatives

β-Carboline derivatives inhibited both indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase activities from various sources. Among them, norharman is most potent for both enzymes from mammalian sources. Kinetic studies revealed that norharman is uncompetitive (K_i = 0.12 mm) with l-tryptophan for rabbit intestinal indoleamine 2,3-dioxygenase, and linearly competitive (K_i = 0.29 mm) with l-tryptophan for mouse liver tryptophan 2,3-dioxygenase. In addition, some β-carbolines selectively inhibited one enzyme or the other. Pseudomonad tryptophan 2,3-dioxygenase was inhibited by a different spectrum of β-carbolines. Such a selective inhibition by the structure of substrate analogs is more evident by the use of indole derivatives. Indole-3-acetamide, indole-3-acetonitrile and indole-3-acrylic acid exhibited a potent inhibition for mammalian tryptophan 2,3-dioxygenase, while they moderately inhibited the pseudomonad enzyme. However, they showed no inhibition for indoleamine 2,3-dioxygenase. These results suggest the difference of the structures of the active sites among these enzymes from various sources.     

Catalytic properties of the immobilized Aspergillus tamarii xylanase

Xylanase from Aspergillus tamarii was covalently immobilized on Duolite A147 pretreated with the bifunctional agent glutaraldehyde. The bound enzyme retained 54.2% of the original specific activity exhibited by the free enzyme (120 U/mg protein). Compared to the free enzyme, the immobilized enzyme exhibited lower optimum pH, higher optimum reaction temperature, lower energy of activation, higher K_m (Michaelis constant), lower V_max (maximal reaction rate). The half-life for the free enzyme was 186.0, 93.0, and 50.0 min for 40, 50, and 60°C, respectively, whereas the immobilized form at the same temperatures had half-life of 320, 136, and 65 min. The deactivation rate constant at 60°C for the immobilized enzyme is about 6.0 × 10⁻³, which is lower than that of the free enzyme (7.77 × 10⁻³ min). The energy of thermal deactivation was 15.22 and 20.72 kcal/mol, respectively for the free and immobilized enzyme, confirming stabilization by immobilization. An external mass transfer resistance was identified with the immobilization carrier (Duolite A147). The effect of some metal ions on the activity of the free and immobilized xylanase has been investigated. The immobilized enzyme retained about 73.0% of the initial catalytic activity even after being used 8 cycles.     

Tetrameric structure and cellular location of catechol 2,3-dioxygenase

Catechol 2,3-dioxygenase from the meta-cleavage pathway encoded on the TOL plasmid of Pseudomonas putida (pWWO) was investigated by electron microscopy. Negatively stained samples of the purified catechol 2,3-dioxygenase revealed that the enzyme consists of four subunits arranged in a tetrahedral conformation. Monoclonal antibodies raised against catechol 2,3-dioxygenase showed highly specific reactions and were used to localize the enzyme in Escherichia coli (pAW31) and P. putida (pWWO), using the protein A-gold technique carried out as a post-embedding immunoelectron microscopy procedure. Our in situ labeling studies revealed a cytoplasmic location of the catechol 2,3-dioxygenase in both cell types.Abbreviations C23O Catechol 2,3-dioxygenase - 3MB 3 Methylbenzoate - AK1 Anti-C23O-IgG-antibody - G Gold particle