6-hydroxypicolinic Acid Research Articles

A 3D Coordination Polymer Based on Syn-Anti Bridged [Mn(RCOO)2]n Chains Showing Spin-Canting with High Coercivity and an Ordering Temperature of 14 K

A new 3D manganese(II) coordination polymer, formulated as [Mn3(HL)6] (1) (where H2L = 6-hydroxypicolinic acid), has been hydrothermally synthesized and characterized by single-crystal X-ray crystallographic analysis along with other spectroscopic and magnetic techniques. Structural analysis shows that the compound crystallizes in the monoclinic C2/c space group and is a non-porous 3D coordination polymer formed by three different Mn(II) centres connected by 6-hydroxypicolinic acid ligands in their keto form. Each Mn(II) centre shows a distorted octahedral coordination environment. Neighbouring Mn(II) centres are connected by two different syn-anti bridging carboxylate groups to form regular coordination chains. There are two different [Mn2(RCOO)2] units along the chain, formed by two crystallographically independent Mn centres (Mn1 and Mn2). These chains are further connected by HL− ligands to form a 3D coordination network. Interestingly, both the hydroxy and the carboxylate groups of the ligands are deprotonated and coordinated to the metal centres, whereas the pyridyl group is protonated and uncoordinated, although it participates in strong hydrogen bonding interactions with oxygen atoms of the HL− ligand, as shown by the Hirshfeld surface analysis. Both the absorption and emission spectra of the compound have also been measured. Variable temperature magnetic studies reveal the presence of a spin-canted antiferromagnetic behaviour with a high coercivity of 40 mT at 2 K and an ordering temperature of 14 K.

Xinfangfangia pollutisoli sp. nov., Isolated from Clopyralid-Contaminated Soil.

With the aim of isolating clopyralid-degrading bacterial species for potential bioremediation, a pale-yellow, Gram-negative, rod-shaped, and non-motile designated as Clo-40T was isolated from soil which was about 10years use of clopyralid in Zaozhuang city, Shandong province. Growth occurred within the ranges from 10 to 40°C and 0-2.5% (w/v) NaCl. Strain could completely degrade 50mg/L clopyralid within 2days after induction and formed 3, 6-hydroxypicolinic acid, a major clopyralid metabolite, hydrolyze esculin, and reduce nitrates to nitrites, but could not hydrolyze gelatin. Based on phylogenetic analysis, strain clustered within the genus Xinfangfangia clade and branched with Xinfangfangia humi IMT-291T (97.6%) and Xinfangfangia soli ZQBWT (96.9%). Genome sequencing revealed a genome size of 4.41 Mbp and G + C content of 67.3%. The average nucleotide ANI values of strain with respect to X. humi IMT-291T and X. soli ZQBWT were 77.5% and 76.9%, respectively. The DDH estimated values between strain Clo-40T and X. humi IMT-291T and X. soli ZQBWT were 20.5% and 20.0%, respectively. The predominant fatty acids (> 5% of the total fatty acids) were C18:1 w7c (42.9%), C16:0 (28.8%), C17:0 cyclo (13.0%), and C14:0 (7.0%). The major polar lipids were identified as phosphatidylethanolamine, phosphatidylglycerol, unidentified phospholipid, unidentified glycolipid, and unidentified lipids. The predominant respiratory quinone was Q-10. Based on data from phenotypic, chemotaxonomic, and genotypic analyses in this study, strain Clo-40T represent a novel species in the genus of Xinfangfangia, for which the name Xinfangfangia pollutisoli sp. nov. is proposed. The type strain is Clo-40T (= KCTC 92089T = GDMCC 1.2845T).

Biodegradation of quinolinic acid by a newly isolated bacterium Alcaligenes faecalis strain JQ191

Abstract Quinolinic acid (QA) is a pyridine derivative that can be found in many organisms and is widely used in the chemical industry. However, QA possesses excitotoxic properties. To date, the catabolism of QA mediated by microorganisms has rarely been reported. In this study, a QA-degrading strain (JQ191) was isolated from sewage sludge. Based on phenotypic and 16S rRNA gene phylogenetic analysis, the strain was identified as Alcaligenes faecalis. Strain JQ191 was able to utilize QA as the sole source of carbon and nitrogen for growth. QA-cultured cells of JQ191 completely degrade 200 mg/L QA within 2 days in a mineral salt medium, whereas the LB-cultured cells experienced a 2-day lag period before degrading QA, indicating that the catabolic enzymes involved in QA degradation were induced by QA. 6-Hydroxypicolinic acid (6HPA) was identified as an intermediate of QA degradation by strain JQ191. A 6HPA monooxygenase gene picB was cloned, genetically disrupted, and heterologously expressed, and the results show that picB was responsible for catalyzing 6HPA to 3,6DHPA in JQ191. A new QA mineralization pathway was proposed. This study identifies a new bacterium candidate that has a potential application prospect in the bioremediation of QA-polluted environment, as well as provides new insights into the bacterial catabolism of QA.

Synthesis, structure and magnetic property of a linear trinuclear Dy(III) single molecular magnet

The Dy(III)-based complexes have garnered intense attention in the past decades due to their fascinating structures and varied magnetic properties. Herein a linear trinuclear Dy(III) complex [Dy3(picO)4(Phen)3(H2O)2]·HpicO·H2O (1) (H2picO = 6-Hydroxypicolinic acid; Phen = 1,10-Phenanthroline) was synthesized by hydrothermal reaction, and characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, PXRD and magnetic properties. The three Dy(III) ions are coordinated to three different coordination pockets, leading to different magnetic anisotropy. Magnetic studies reveal that it is a single molecular magnet with slow magnetic relaxation under zero dc field at low temperature dominated by Raman and QTM processes. The energy barriers are 30 K and 39 K for the two relaxation processes under 2000 Oe dc field.

Novel 3,6-Dihydroxypicolinic Acid Decarboxylase-Mediated Picolinic Acid Catabolism in Alcaligenes faecalis JQ135.

Picolinic acid (PA), a typical C-2-carboxylated pyridine derivative, is a metabolite of l-tryptophan and many other aromatic compounds in mammalian and microbial cells. Microorganisms can degrade and utilize PA for growth. However, the precise mechanism of PA metabolism remains unknown. Alcaligenes faecalis strain JQ135 utilizes PA as its carbon and nitrogen source for growth. In this study, we screened a 6-hydroxypicolinic acid (6HPA) degradation-deficient mutant through random transposon mutagenesis. The mutant hydroxylated 6HPA into an intermediate, identified as 3,6-dihydroxypicolinic acid (3,6DHPA), with no further degradation. A novel decarboxylase, PicC, was identified to be responsible for the decarboxylation of 3,6DHPA to 2,5-dihydroxypyridine. Although, PicC belonged to the amidohydrolase 2 family, it shows low similarity (<45%) compared to other reported amidohydrolase 2 family decarboxylases. Moreover, PicC was found to form a monophyletic group in the phylogenetic tree constructed using PicC and related proteins. Further, the genetic deletion and complementation results demonstrated that picC was essential for PA degradation. The PicC was Zn2+-dependent nonoxidative decarboxylase that can specifically catalyze the irreversible decarboxylation of 3,6DHPA to 2,5-dihydroxypyridine. The Km and kcat toward 3,6DHPA were observed to be 13.44 μM and 4.77 s-1, respectively. Site-directed mutagenesis showed that His163 and His216 were essential for PicC activity. This study provides new insights into the microbial metabolism of PA at molecular level.IMPORTANCE Picolinic acid is a natural toxic pyridine derived from l-tryptophan metabolism and other aromatic compounds in mammalian and microbial cells. Microorganisms can degrade and utilize picolinic acid for their growth, and thus a microbial degradation pathway of picolinic acid has been proposed. Picolinic acid is converted into 6-hydroxypicolinic acid, 3,6-dihydroxypicolinic acid, and 2,5-dihydroxypyridine in turn. However, there was no physiological and genetic validation for this pathway. This study demonstrated that 3,6-dihydroxypicolinic acid was an intermediate in picolinic acid catabolism and further identified and characterized a novel amidohydrolase 2 family decarboxylase PicC. PicC was also shown to catalyze the decarboxylation of 3,6-dihydroxypicolinic acid into 2,5-dihydroxypyridine. This study provides a basis for understanding picolinic acid degradation and its underlying molecular mechanism.

Biodegradation of Picolinic Acid by Rhodococcus sp. PA18

Picolinic acid (PA), a C2-carboxylated pyridine derivative, is a significant intermediate used in industrial production. PA is considered hazardous for the environment and human health. In this study, a Gram-positive bacterium, Rhodococcus sp. PA18, which aerobically utilizes PA as a source of carbon and energy, was isolated. The strain completely degraded 100 mg/L PA within 24 h after induction and formed 6-hydroxypicolinic acid (6HPA), a major PA metabolite, which was identified using ultraviolet-visible spectroscopy, high performance liquid chromatography, and liquid chromatography/time of flight-mass spectrometry analyses. The cell-free extracts converted the PA into 6HPA when phenazine methosulfate was used as an electron acceptor. To our knowledge, this is the first report showing that PA can be metabolized by Rhodococcus. In conclusion, Rhodococcus sp. PA18 may be potentially used for the bioremediation of environments polluted with PA.

Biodegradation of Picolinic Acid by a Newly Isolated Bacterium Alcaligenes faecalis Strain JQ135.

We isolated a bacterial strain JQ135 from municipal wastewater, which was capable of efficiently degrading picolinic acid (PA). Based on the physico-biochemical characteristics and 16S rDNA analysis, strain JQ135 was identified as Alcaligenes faecalis. In addition, strain JQ135 produced an orange pigment when cultured in the Luria-Bertani medium, which is different from the previously reported strains of A. faecalis. During the degradation of PA by the resting strain JQ135 cells, only one intermediate, 6-hydroxypicolinic acid (6HPA), was detected by ultraviolet spectrophotometry, high-pressure liquid chromatography, and liquid chromatography-mass spectrometry. A random transposon mutagenesis library of strain JQ135 was constructed. One mutant, Mut-G31, could convert PA into 6HPA without further degradation. The disrupted gene (orf2) was amplified from Mut-G31, and its product showed 32% identity to the 3-deoxy-D-manno-octulosonic acid kinase (KdkA) from Haemophilus influenzae. Results from complementation analysis confirmed that GTG was the initiation codon of the kdkA-like orf2, and that it was essential for PA biodegradation by strain JQ135. This study provides the first genetic evidence for the bacterial degradation of PA.

Aerobic Biodegradation of 2-Picolinic Acid by a Comamonas sp.

A strain was able to use 2-picolinic acid (2-PA) as a sole source of carbon, nitrogen and energy under aerobic conditions was isolated in this paper. Based on 16S rRNA gene sequence analysis, this strain was identified as Comamonas sp. and named as ZD3. The effects of pH and initial concentrations of 2-PA on the degrading capacity of ZD3 were investigated. It was found that ZD3 degraded 2-PA effectively under a pH range of 5.0 to 9.0, in which 7.0 was proved to be the optimal value. When the initial concentration of 2-PA was 100, 200, 400, 600 and 800 mg/L, ZD3 completely degraded 2-PA within 10, 18, 22, 78 and 114 h, respectively. Zero order kinetic model expressed the degradation behavior of 2-PA by ZD3 well. It was observed that under the concentration range of 100 to 400 mg/L, the degradation rate constant increased with the increase in concentration and reached the maximum at 400 mg/L. However, under the concentration range of 600 to 800 mg/L, the degradation rate constant began to decrease, indicating an inhibitory effect. Moreover, ultraviolet scanning and high performance liquid chromatography ion trap timeof- flight mass spectrometry showed that during the degradation of 2-PA the first reaction was α hydroxylation so that 6-hydroxy picolinic acid (6-HPA) was produced.

Rhenium(III), (IV) and (V) complexes with 6-hydroxypicolinic acid

The reaction of trans-[ReOBr3(PPh3)2] with 6-hydroxypicolinic acid (H2hpa) in ethanol led to the isolation of the ReIVReIV dimer (μ-O)(μ-hpa)2[Re2Br(OEt)(PPh3)2] (1). Each hpa2− anion acts as a bridging ligand with the coordination of a neutral pyridol oxygen to one rhenium ion, and the coordination of a carboxylate oxygen and a pyridinate nitrogen to the other rhenium ion. By using [ReOCl3(PPh3)2] as precursor in ethanol, two products were isolated, i.e. (μ-Cl)(μ-O)(μ-hpa)[ReIV2Cl2(OEt)(PPh3)2] (2) and [ReIIICl2(Hhpa)(PPh3)2] (3). The complexes cis-[ReOX2(Hhpa)(PPh3)] (X=Br (4); Cl (5)) were the only products formed by the reaction of [ReOX3(PPh3)2] with H2hpa in acetonitrile. The bromide equivalent of 3, i.e. [ReIIIBr2(Hhpa)(PPh3)2] (6), was obtained from the reaction of [ReOBr3(PPh3)2] with H2hpa in 2-propanol. Coordination of Hhpa− in 3–6 occurs through the carboxylate oxygen and neutral pyridyl nitrogen. In addition to the X-ray crystal structures, infra-red, 1H NMR, electrochemical and electronic properties are also reported.

Substituent effect on the proton-related phenomena and chelation behavior of hydroxypicolinic compounds: a DFT investigation

Comparative study on kinetics and thermodynamics of proton-related reactions of hydroxypicolinic acids has been carried out using density functional theory associated with polarizable continuum model of solvation. Mechanisms for such reactions have been established. Both 3- and 4-hydroxypicolinic acid prefer zwitterionic forms to normal forms. For 6-hydroxypicolinic acid, keto forms are highly preferred. The pK a values and UV/Vis bands predicted for some picolinic compounds agree with the experiment. 5-Hydroxypicolinate shows the highest preference for complexation with copper(II) but 6-hydroxypolinate gives rise to the most stable complex. Kinetic stability of the trans-isomer relative to the cis-isomer of the complexes has been evaluated. UV/Vis spectral data predicted for some picolinate complexes are also in agreement with the previous experiment.

Computational study of the intramolecular proton transfer between 6-hydroxypicolinic acid tautomeric forms and intermolecular hydrogen bonding in their dimers

This paper is a density functional theory (DFT) calculation of intramolecular proton transfer (IPT) in 6-hydroxypicolinic acid (6HPA, 6-hydroxypyridine-2-carboxylic acid) tautomeric forms. The transition state for the enol-to-keto transition is reported in the gas phase and in four different solvents. The planar and non-planar dimer forms of 6HPA keto and enol, respectively, were also studied in the gas phase The IPT reactions and dimerization processes were studied at the B3LYP/6-31++G(d) level of the theory. The influence of the solvent on the tautomerization reaction of 6HPA was examined using the conductor-polarizable continuum model (CPCM). The IPT reaction in the gas phase is almost the same as in solution. The calculated dimerization energies show that the stability of 6HPA tautomer dimer structures is directly affected by the distance of intermolecular hydrogen bonding and electrostatic potential (ESP) value in the tautomer dimer.

Synthesis and Characterization of a Copper(II) Complex with 6-Hydroxypicolinic Acid and 3-Picoline

A copper(II) complex with 6-hydroxypicolinic acid (6-OHpicH) and 3-picoline (3-pic), [Cu(6- OHpic)2(3-pic)2] (1), was prepared by recrystallization of [Cu(6-OHpic)2(H2O)2] from 3- picoline and characterized by IR spectroscopy and thermal methods (TGA/DTA and DSC). The molecular and crystal structure of 1 was determined by single-crystal X-ray structural analysis. The copper(II) ion in 1 has a tetragonally compressed octahedral coordination environment, achieved by two N, O-bidentate 6-hydroxypicolinate ligands and by two 3-picoline molecules in trans positions. The crystal structure of 1 exhibits one strong intermolecular O–H...O hydrogen bond, one weak intermolecular C–H...O hydrogen bond and one C– H...π interaction. Molecules of 1 are assembled into a 2D network in the (1 0 -1) plane, giving rise to C11(8) graph-set motif. These 2D networks are further assembled into 3D architecture only by weak Van der Waals interactions. A thermogravimetric study showed the initial loss of two coordinated 3-picoline molecules in 1, followed by a complete decomposition of the compound.

Disappearing and Concomitant Polymorphism of Nickel(II) Complexes with 6-Hydroxypicolinic Acid. Structural and Density Functional Theory Studies

The recrystallization of the complex [Ni(6-OHpic)2(H2O)2] (1) from a mixture of pyridine and acetone led to the formation of three different polymorphs of [Ni(6-OHpic)2(py)2]. The stable monoclinic polymorph 3 was obtained by evaporation of the solution, while the slow diffusion of acetone into the pyridine solution of 1 yielded the orthorhombic polymorph 2. Further attempts to prepare 2 again were unsuccessful (disappearing polymorph). The new pseudopolymorph [Ni(6-OHpic)2(py)2]·py (4) was obtained under the same conditions as 3, but again not reproducibly (concomitant and a disappearing polymorph). trans-[Ni(6-OHpic)2(py)2] formed one intramolecular O−H···O hydrogen bond and one intermolecular one to afford dimers (3) and infinite zigzag chains (2). When two intramolecular O−H···O hydrogen bonds were present, the dimers were held by π−π stacking (4). Density functional theory calculations showed trans-[Ni(6-OHpic)2(py)2] to be the most stable isomer. The hydrogen bonded dimers are the most stable motif,...

Aerobic degradation of 2-picolinic acid by a nitrobenzene-assimilating strain: Streptomyces sp. Z2

Streptomyces sp. Z2 was isolated from nitrobenzene contaminated activated sludge, which utilized nitrobenzene as a sole source of carbon, nitrogen, and energy under aerobic condition. It was found that besides nitrobenzene strain Z2 can degrade 2-picolinic acid. Strain Z2 completely degraded 2-picolinic acid with initial concentration of 500 mg/L, 1000 mg/L, 1500 mg/L, 2000 mg/L, 2500 mg/L, and 3000 mg/L within 36 h, 50 h, 72 h, 100 h, 136 h, and 180 h, respectively. Kinetics of 2-picolinic acid degradation was described using the Andrews equation. The kinetic parameters were as follows: q max = 3.81 h −1, K s = 83.10 mg/L, and K i = 252.11 mg/L. During the biodegradation process, Z2 transformed 2-picolinic acid into a product which was identified as 6-hydroxy picolinic acid by UV–vis spectrometry, 1H nuclear magnetic resonance spectroscopy, and mass spectrometry. 6-Hydroxy picolinic acid was then cleaved and mineralized with release of ammonia.

Dimethylthallium(III) complexes with picolinic acid and its hydroxyl derivatives

The reaction of dimethylthallium(III) hydroxide with picolinic acid (Hpic), 3-hydroxypicolinic acid (H 23hpic) and 6-hydroxypicolinic acid (H 26hpic) in an aqueous/methanol mixture afforded the complexes [TlMe 2(pic)] ( 1), [TlMe 2(H3hpic)] ( 2) and [TlMe 2(H6hpic)] ( 3), respectively. Complex 3′, [NaTlMe 2(6hpic) 2] n , was obtained as a minor product from a methanolic solution of 3. Compounds 1– 3 were characterized by IR and Raman spectroscopy and, in the cases of 1, 2 and 3′, by single-crystal X-ray diffraction. Complex 3′ is the first example of an H6hpic − heterobimetallic compound to be isolated. The 1H and 13C NMR spectra of 1 and 2 are also discussed.

Synthesis and structure of cobalt(II) complexes with hydroxyl derivatives of pyridinecarboxylic acids: Conformation analysis of ligands in the solid state

Cobalt(II) complexes of 6-hydroxypicolinic acid (6-OHpicH), namely [Co(6-OHpic) 2(H 2O) 2] ( 1) and [Co(6-OHpic) 2(4-pic) 2]·4-pic ( 2), and of 2-hydroxynicotinic acid (2-OHnicH), [Co(2-OHnic) 2(H 2O) 2] ( 3) were prepared. The crystal structures of free 6-hydroxypicolinic acid monohydrate 6-OHpicH·H 2O ( 4), and the novel polymorph of 2-hydroxynicotinic acid 2-OHnicH ( 5) and complex 2 were determined by X-ray crystal structure analysis. All compounds were characterized by IR-spectroscopy and thermal methods (TGA/DSC) and data are in agreement with the structure analysis. It was established that 4 and 5 exist in solid state in keto tautomeric form. For 2, structure analysis revealed N,O-chelating mode of 6-hydroxypicolinic acid.

Photochemistry of 6-chloro and 6-bromopicolinic acids in water. Heterolytic vs. homolytic photodehalogenation

The photochemistry of 6-chloro and 6-bromopicolinate ions ( and , respectively) was investigated by product studies and ns laser flash photolysis (LFP). In deoxygenated pH 5.4 water, yields 6-hydroxypicolinic acid (70%) and a substituted pyrrole. In 2-propanol-water (1 : 1) mixture, the reaction yields, very unselectively, 6-hydroxypicolinic acid, 2-carboxypyridine, pyridine and bipyridines. Photolysis of aqueous leads to 6-hydroxypicolinic acid (78%) and hydroxybipyridines. Oxygen suppresses the photolysis of but does not affect that of . By LFP, we detected a short-lived transient at the pulse end from (lambda(max)= 305 nm, k=(2.8 +/- 0.2)x 10(5) s(-1), epsilonphi= 2200 +/- 200 dm3 mol(-1) cm(-1)). This is quenched either by oxygen or methyl acrylate and thus assigned to the triplet excited state. The triplet excited state of is detected at pH 1 only (lambda(max)= 320 nm, k > 3 x 10(7) s(-1)). The radical ion Cl2- could be successfully detected by photolysing in 2-propanol-water (1 : 1) in the presence of Cl-. Similarly, Br2- could be detected by irradiating aqueous in the presence of Br-. These results show that the photodehalogenation of is heterolytic in water and mainly homolytic in 2-propanol-water mixtures while that of is both heterolytic and homolytic in water. A mechanism in which the triplet excited state undergoes homolysis of the C-X bond and subsequent electron transfer from the carboxypyridyl radical to the halogen atom to form an ion pair may account for these observations.

Supramolecular architectures from the self-assembly of lanthanide ions with 6-hydroxypicolinic acid and 1,10-phenanthroline

Three new lanthanide complexes, [La(HpicO) 3(phen)(H 2O)] n ( 1) and Ln 3(picO) 4(phen) 3(H 2O) 2·HpicO·0.5H 2O (Ln=Er ( 2), Yb ( 3)) were synthesized by the hydrothermal reactions and characterized by single crystal X-ray diffraction, elemental analysis and IR spectrum. In complex 1, each La(III) ion is 10-coordinated and HpicO − ligands link the metal ions into 1D zigzag chains. Complexes 2 and 3 are isomorphous, and there are three crystallographically independent Ln(III) ions in the asymmetric unit. The N–H⋯O and O–H⋯O hydrogen bonds and π–π stacking interactions in these complexes result in the formation of 3D supramolecular architectures.

The reactions of 2-hydroxypyridine ligands with Re 2Cl 4(μ-dppm) 2 (dppm=Ph 2PCH 2PPh 2) that lead to 2-pyridonate complexes

2-Hydroxypyridine (Hhp), 2-hydroxynicotinic acid (HnicOH) and 6-hydroxypicolinic acid (HpicOH) react with Re 2Cl 4(μ-dppm) 2 (dppm=Ph 2PCH 2PPh 2) to afford the complexes Re 2(η 2-hp)Cl 3(μ-dppm) 2 ( 1), Re 2(η 2-HnicO)Cl 3(μ-dppm) 2 ( 2) and Re 2(μ-picO) 2(μ-dppm) 2 ( 3). The identities of 1 and 2 have been established by single-crystal X-ray structure determinations (Re–Re distances of 2.2602(3) and 2.2539(3) Å, respectively) and they are shown to have unsymmetrical structures with staggered rotational geometries and trans, cis coordination of the pair of μ-dppm ligands. The crystal of 2 that was used in the structure determination was found to be of composition 2Re 2(η 2-HnicO)Cl 3(μ-dppm) 2 · Re 2Cl 6(μ-dppm) 2 · 2.906CH 2Cl 2. The structure of Re 2Cl 6(μ-dppm) 2 in this crystal is compared with structures reported in the literature for other crystals that contain this edge-sharing bioctahedral dirhenium(III) complex.

Quinolinate dehydrogenase and 6-hydroxyquinolinate decarboxylase involved in the conversion of quinolinic acid to 6-hydroxypicolinic acid by Alcaligenes sp. strain UK21.

In the conversion of quinolinic acid to 6-hydroxypicolinic acid by whole cells of Alcaligenes sp. strain UK21, the enzyme reactions involved in the hydroxylation and decarboxylation of quinolinic acid were examined. Quinolinate dehydrogenase, which catalyzes the first step, the hydroxylation of quinolinic acid, was solubilized from a membrane fraction, partially purified, and characterized. The enzyme catalyzed the incorporation of oxygen atoms of H(2)O into the hydroxyl group. The dehydrogenase hydroxylated quinolinic acid and pyrazine-2,3-dicarboxylic acid to form 6-hydroxyquinolinic acid and 5-hydroxypyrazine-2,3-dicarboxylic acid, respectively. Phenazine methosulfate was the preferred electron acceptor for quinolinate dehydrogenase. 6-Hydroxyquinolinate decarboxylase, catalyzing the nonoxidative decarboxylation of 6-hydroxyquinolinic acid, was purified to homogeneity and characterized. The purified enzyme had a molecular mass of approximately 221 kDa and consisted of six identical subunits. The decarboxylase specifically catalyzed the decarboxylation of 6-hydroxyquinolinic acid to 6-hydroxypicolinic acid, without any co-factors. The N-terminal amino acid sequence was homologous with those of bacterial 4,5-dihydroxyphthalate decarboxylases.