The hydroxylation of nicotinic acid by Pseudomonas fluorescens

Biodegradation of 3-methylpyridine by an isolated strain, Gordonia rubripertincta ZJJ

Methylpyridines are a class of highly toxic pyridine derivatives. In this study, a novel degrading bacterium was isolated for 3-methylpyridine (3-MP) degradation (Gordonia rubripertincta ZJJ, GenBank accession NO. OP430847.1; CCTCC M 2022975). The maximum specific degradation rate, half-saturation constant and inhibition constant were fitted to be 0.48 h-1, 88.3 mg L-1 and 924.0 mg L-1, respectively. During 3-MP biodegradation, the lost total organic carbon was transformed into CO2 (67.4 %) and biomass (32.6 %), and ammonia nitrogen was almost the sole inorganic species with a conversion rate of 36.3 %. Three metabolic pathways were possibly involved in 3-MP degradation: I) methyl oxidation followed by ring hydroxylation and hydrogenation; II) rupture of C=C and C-N bonds after ring reduction; III) initial ring hydroxylation. The study not only provides a novel strain for the high-efficient degradation of 3-MP, but also contributes to an in-depth understanding of 3-MP biotransformation.

Mechanism of 6-Hydroxynicotinate 3-Monooxygenase, a Flavin-Dependent Decarboxylative Hydroxylase Involved in Bacterial Nicotinic Acid Degradation

6-Hydroxynicotinate 3-monooxygenase (NicC) is a Group A FAD-dependent monooxygenase that catalyzes the decarboxylative hydroxylation of 6-hydroxynicotinic acid (6-HNA) to 2,5-dihydroxypyridine (2,5-DHP) with concomitant oxidation of NADH in nicotinic acid degradation by aerobic bacteria. Two mechanisms for the decarboxylative hydroxylation half-reaction have been proposed [Hicks, K., et al. (2016) Biochemistry 55, 3432-3446]. Results with Bordetella bronchiseptica RB50 NicC here show that a homocyclic analogue of 6-HNA, 4-hydroxybenzoic acid (4-HBA), is decarboxylated and hydroxylated by NicC with a 420-fold lower catalytic efficiency than is 6-HNA. The ¹³( V/ K), measured with wild-type NicC by isotope ratio mass spectrometry following the natural abundance of ¹³C in the CO₂ product, is inverse for both 6-HNA (0.9989 ± 0.0002) and 4-HBA (0.9942 ± 0.0004) and becomes negligible (0.9999 ± 0.0004) for 5-chloro-6-HNA, an analogue that is 10-fold more catalytically efficient than 6-HNA. Covalently bound 6-HNA complexes of NicC are not observed by mass spectrometry. Comparative steady-state kinetic and K_d^6HNA analyses of active site NicC variants (C202A, H211A, H302A, H47E, Y215F, and Y225F) identify Tyr215 and His47 as critical determinants both of 6-HNA binding ( K_d^Y215F/ K_d^WT > 240; K_d^H47E/ K_d^WT > 350) and in coupling rates of 2,5-DHP and NAD⁺ product formation ([2,5-DHP]/[NAD⁺] = 1.00 (WT), 0.005 (Y215F), and 0.07 (H47E)]. Results of these functional analyses are in accord with an electrophilic aromatic substitution reaction mechanism in which His47-Tyr215 may serve as the general base to catalyze substrate hydroxylation and refine the structural model for substrate binding by NicC.

Identification and characterization of a new three-component nicotinic acid hydroxylase NahAB1 B2 from Pusillimonas sp. strain T2

Nicotinic acid (NA) is ubiquitous in nature and its microbial degradation mechanisms are diverse. In this study, Pusillimonas sp. strain T2 was found to be capable of utilizing NA as sole carbon and nitrogen sources. This strain could completely degrade 300 mg l^-1 NA within 3·5 h at 30°C and pH 7·0 and one of the degradation intermediate of NA was identified as 6-hydroxynicotinic acid (6HNA). The draft genome sequences of strain T2 were determined to have a total length of 3·3 M bp and 3054 proteins were predicted. The encoding genes of three-component NA hydroxylase (NahAB₁ B₂ ) genes were identified. The nahAB₁ B₂ genes were heterologously expressed in the non-NA-degrading Shinella sp. strain HZN7. The recombinant HZN7-pBBR-nahAB₁ B₂ converted NA into equimolar 6HNA, while the recombinants HZN7-pBBR-nahAB₁ (lacking component B₂ ) and HZN7-pBBR-nahAB₂ (lacking component B₁ ) could not convert NA. Cell-free extracts of HZN7-pBBR-nahAB₁ B₂ exhibited NA hydroxylase activity. After addition of an artificial electron acceptor (such as phenazine methosulphate, PMS), the NA hydroxylase activity was significantly increased. The K_m and V_max values for NA were 65·94 μmol l^-1 and 260·80 ± 5·69 mU mg^-1 , respectively, using PMS as an electron acceptor. This study provides a novel insight into the NA degradation by bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Nicotinic acid (NA) serves as a model system for the degradation of N-heterocyclic aromatic compounds and the microbial degradation mechanisms are diverse. This is the first time that a three-component hydroxylase has been identified. This study provides a novel insight into the NA degradation by bacteria.

Two Novel Sets of Genes Essential for Nicotine Degradation by Sphingomonas melonis TY

Nicotine is a type of environmental pollutant present in the tobacco waste that is generated during tobacco manufacturing. Sphingomonas melonis TY can utilize nicotine as a sole source of carbon, nitrogen and energy via a variant of the pyridine and pyrrolidine pathway (the VPP pathway). In this study, we report the identification of two novel sets of genes, ndrA1A2A3, and ndrB1B2B3B4, which are crucial for nicotine degradation by strain TY. ndrA1A2A3 and ndrB1B2B3B4 exhibit similarity with both nicotine dehydrogenase ndh from Arthrobacter nicotinovorans and nicotine hydroxylase vppA from Ochrobactrum sp. SJY1. The transcriptional levels of ndrA1A2A3 and ndrB1B2B3B4 in strain TY were significantly upregulated in the presence of nicotine. Furthermore, ndrA1 or ndrB2 knockout resulted in a loss of the ability to degrade nicotine, whereas gene complementation restored the capacity of each mutant to utilize nicotine for growth. Biodegradation assays indicated that the mutant strains retained the ability to degrade the first intermediate in the pathway, 6-hydroxynicotine (6 HN). However, heterologous expression of ndrA1A2A3 and ndrB1B2B3B4 did not confer nicotine dehydrogenase activity to E. coli DH5α, Pseudomonas putida KT2440 or Sphingomonas aquatilis. These results provide information on the VPP pathway of nicotine degradation in S. melonis TY, and we conclude that these two sets of genes have essential functions in the conversion of nicotine to 6 HN in strain TY.

The microbial metabolism of thiophen-2-carboxylate

1. An organism was isolated by enrichment culture that was capable of using thiophen-2-carboxylate as sole source of carbon, energy and sulphur for growth. 2. Analysis of the cellular protein after growth of the organism on thiophen-2-[(14)C]carboxylate showed that only glutamate, proline and arginine were labelled. All the radioactivity in the glutamate was confined to C-1. 3. In the presence of 2.1 mm-arsenite, suspensions of the organism converted thiophen-2-[(14)C]carboxylate into (14)C-labelled 2-oxoglutarate which had the same specific radioactivity as the starting material. 4. Cell-free extracts of the organism catalysed the release of (14)CO(2) from thiophen-2-[(14)C]carboxylate. This activity was largely dependent on the presence of ATP and CoA and was stimulated by NAD(+) and Mg(2+). Inclusion of hydroxylamine resulted in the appearance of thiophen-2-carbohydroxamic acid, indicating that the ATP and CoA were involved in the formation of the CoA ester of thiophen-2-carboxylate. 5. High-speed centrifuging of cell-free extracts resulted in supernatants with decreased thiophen-2-carboxylate-degrading activity. Activity was restored by the addition of the high-speed pellet or by Methylene Blue. 6. The metabolism of the CoA ester of thiophen-2-carboxylate by cell-free extracts could be linked to the anaerobic reduction of Methylene Blue. 7. The sulphur atom of the thiophen nucleus was converted into sulphate by growing cultures and resting suspensions of the organism. 8. A degradative pathway is proposed involving the hydroxylation (at C-5) of the CoA ester of thiophen-2-carboxylate followed by further metabolism to 2-oxoglutarate and sulphate.

Molybdenum Involvement in Aerobic Degradation of 2-Furoic Acid by Pseudomonas putida Fu1

An organism identified as Pseudomonas putida was isolated from an enrichment culture with 2-furoic acid as its sole source of carbon and energy. The organism contained a 2-furoyl-coenzyme A (CoA) synthetase to form 2-furoyl-CoA and a 2-furoyl-CoA dehydrogenase to form 5-hydroxy-2-furoyl-CoA as the first two enzymes involved in the degradation. Tungstate, the specific antagonist of molybdate, decreased growth rate and consumption of 2-furoic acid but had no influence on growth with succinate. Correspondingly, the 2-furoyl-CoA dehydrogenase activity decreased when the organism was grown on 2-furoic acid in the presence of increasing amounts of tungstate. The addition of molybdate reversed the negative effect on 2-furoyl-CoA dehydrogenase activity, which points to the involvement of a molybdoenzyme in this reaction. Both enzymes studied were inducible. No plasmid was detected in this organism.

Cloning, expression and functional analysis of nicotinate dehydrogenase gene cluster from Comamonas testosteroni JA1 that can hydroxylate 3-cyanopyridine

A nicotinate dehydrogenase (NaDH) gene cluster was cloned from Comamonas testosteroni JA1. The enzyme, termed NaDH(JA1), is composed of 21, 82, and 46 kDa subunits, respectivley containing [2Fe2S], Mo(V) and cytochrome c domains. The recombinant NaDH(JA1) can catalyze the hydroxylation of nicotinate and 3-cyanopyridine. NaDH(JA1) protein exhibits 52.8% identity to the amino acid sequence of NaDH(KT2440) from P. putida KT2440. Sequence alignment analysis showed that the [2Fe2S] domain in NaDH(JA1) had a type II [2Fe-2S] motif and a type I [2Fe-2S] motif, while the same domain in NaDH(KT2440) had only a type II [2Fe-2S] motif. NaDH(KT2440) had an additional hypoxanthine dehydrogenase motif that NaDH(JA1) does not have. When the small unit of NaDH(JA1) was replaced by the small subunit from NaDH(KT2440), the hybrid protein was able to catalyze the hydroxylation of nicotinate, but lost the ability to catalyze hydroxylation of 3-cyanopyridine. In contrast, after replacement of the small subunit of NaDH(KT2440) with the small subunit from NaDH(JA1), the resulting hybrid protein NaDH(JAS+KTL) acquired the ability to hydroxylate 3-cyanopyridine. The subunits swap results indicate the [2Fe2S] motif determines the 3-cyanopyridine hydroxylation ability, which is evidently different from the previous belief that the Mo motif determines substrate specificity.

Cloning, heterologous expression, and functional characterization of the nicotinate dehydrogenase gene from Pseudomonas putida KT2440

6-hydroxynicotinate can be used for the production of drugs, pesticides and intermediate chemicals. Some Pseudomonas species were reported to be able to convert nicotinic acid to 6-hydroxynicotinate by nicotinate dehydrogenase. So far, previous reports on NaDH in Pseudomonas genus were confused and contradictory each other. Recently, Ashraf et al. reported an NaDH gene cloned from Eubacterium barkeri and suggested some deducted NaDH genes from other nine bacteria. But they did not demonstrate the activity of recombinant NaDH and did not mention NaDH gene in Pseudomonas. In this study we cloned the gene of NaDH, ndhSL, from Pseudomonas putida KT2440. NdhSL in P. putida KT2440 is composed of two subunits. The small subunit contains [2Fe2S] iron sulfur domain, while the large subunit contains domains of molybdenum cofactor and cytochrome c. Expression of recombinant ndhSL in P. entomophila L48, which lacks the ability to produce 6-hydroxynicotinate, enabled the resting cell and cell extract of engineering P. entomophila L48 to hydroxylate nicotinate. Gene knockout and recovery studies further confirmed the ndhSL function.

Biotreatment of waste gas containing pyridine in a biofilter

Industrial waste gas emissions containing pyridine are generated from pyridine manufacturing industries, and in industrial operations where pyridine is used as a solvent, as an intermediate for synthesis and as a catalyst for a variety of applications. Pyridine has unpleasant fishy odor with an odor index of 2390 and waste gaseous emissions containing pyridine require proper treatment prior to discharge. A biofilter, packed with compost and wood chips and inoculated with Pseudomonas pseudoalcaligenes-KPN for enrichment of pyridine-degrading microorganisms, was operated on a continuous feed basis for a period of more than 2 years. The results indicate that the biofilter medium with optimal moisture content of 68% and an effective bed retention time (EBRT) of 28.50s could degrade pyridine effectively (>99%) at a loading of 434 g pyridine m(-3)h(-1). The treated waste gas was also found to be free from pyridine odor.

Biodegradation of pyridine in a completely mixed activated sludge process

A potential bacterial culture (P1), isolated from garden soil and identified as Pseudomonas pseudoalcaligenes-KPN, was used as a starter seed to develop the biomass in a completely mixed activated sludge (CMAS) reactor and the system was evaluated for treatment of wastewater containing pyridine. The results of this study indicate that pyridine could be degraded efficiently at a loading of 0.251 kg pyridine kg MLSS(-1) d(-1) (0.156 kg TOC kg MLSS(-1) d(-1)) and at an optimal hydraulic retention time (HRT) of 24 h. Pyridine was used as the sole source of carbon and nitrogen by the biomass. Ammonia-nitrogen (NH3-N) was formed due to the metabolism of the pyridine ring. In the present investigation, the performance of CMAS with reference to pyridine biodegradation and the bio-kinetic constants for the biodegradation of pyridine, in a continuous system, were computed. The results indicate that a CMAS system inoculated with P. pseudoalcaligenes-KPN, under optimum conditions of HRT and pyridine loading, gives a yield coefficient of (Y) 0.29, decay coefficient (Kd) 0.0011 d(-1), maximum growth rate constant (mumax) 0.108 d(-1) and saturation rate constant (Ks) 5.37 mg L(-1) for pyridine.

Microbial metabolism of pyridine, quinoline, acridine, and their derivatives under aerobic and anaerobic conditions

Our review of the metabolic pathways of pyridines and aza-arenes showed that biodegradation of heterocyclic aromatic compounds occurs under both aerobic and anaerobic conditions. Depending upon the environmental conditions, different types of bacteria, fungi, and enzymes are involved in the degradation process of these compounds. Our review indicated that different organisms are using different pathways to biotransform a substrate. Our review also showed that the transformation rate of the pyridine derivatives is dependent on the substituents. For example, pyridine carboxylic acids have the highest transformation rate followed by mono-hydroxypyridines, methylpyridines, aminopyridines, and halogenated pyridines. Through the isolation of metabolites, it was possible to demonstrate the mineralization pathway of various heterocyclic aromatic compounds. By using 14C-labeled substrates, it was possible to show that ring fission of a specific heterocyclic compound occurs at a specific position of the ring. Furthermore, many researchers have been able to isolate and characterize the microorganisms or even the enzymes involved in the transformation of these compounds or their derivatives. In studies involving 18O labeling as well as the use of cofactors and coenzymes, it was possible to prove that specific enzymes (e.g., mono- or dioxygenases) are involved in a particular degradation step. By using H2 18O, it could be shown that in certain transformation reactions, the oxygen was derived from water and that therefore these reactions might also occur under anaerobic conditions.

One molecule of molybdopterin guanine dinucleotide is associated with each subunit of the heterodimeric Mo-Fe-S protein transhydroxylase of Pelobacter acidigallici as determined by SDS/PAGE and mass spectrometry

The molybdenum-containing iron-sulfur protein 1,2,3,5-tetrahydroxybenzene: 1,2,3-trihydroxybenzene hydroxyltransferase (transhydroxylase) of Pelobacter acidigallici was investigated by various techniques including mass spectrometry and electron paramagnetic resonance. Mass spectrometry confirmed that the 133-kDa protein is a heterodimer consisting of an alpha subunit (100.4 kDa) and a beta subunit (31.3 kDa). The presence of a molybdenum cofactor was documented by fluorimetric analysis of the oxidized form A of molybdopterin. The enzyme contained 1.55 +/- 0.14 mol pterin and 0.92 +/- 0.25 mol molybdenum/mol enzyme (133 kDa). Alkylation of the molybdenum cofactor with iodoacetamide formed di(carboxamidomethyl)-molybdopterin. Upon acid hydrolysis, 1.4 mol 5'GMP/mol enzyme (133 kDa) was released indicating that molybdenum is bound by a molybdopterin guanine dinucleotide. The alpha and beta subunits were separated by preparative gel electrophoresis. Both subunit fractions were free of molybdenum but contained equal amounts of a fluorescent form of the molybdenum cofactors. Mass spectrometry at various pH values revealed that an acid-labile cofactor was released from the large subunit and also from the small subunit. At X-band, 5-25 K, transhydroxylase (as isolated) showed minor EPR resonances with apparent g values around 4.3, 2.03 and, depending on the preparation, a further signal at g of approximately 1.98. This signal was still detectable above 70 K and was attributed to a Mo(V) center. Upon addition of dithionite, a complex set of intense resonances appeared in the region g 2.08-1.88. From their temperature dependence, three distinct sites could be identified: the Fe-S center I with gx,y,z at approximately 1.875, 1.942 and 2.087 (gav 1.968, detectable < 20 K); the Fe-S center II with gx,y,z at approximately 1.872, 1.955 and 2.051 (gav 1.959, detectable > 20 K); and the Mo(V) center consisting of a multiple signal around g 1.98 (detectable > 70 K).

Selenium requirement for active xanthine dehydrogenase from Clostridium acidiurici and Clostridium cylindrosporum

The xanthine dehydrogenase of Clostridium acidiurici and C. cylindrosporum was assayed with methyl viologen as acceptor. In C. acidiurici the basal activity level was about 0.3 mumol/min x mg of protein. Cells grown on uric acid in the presence of 10(-7) M selenite showed a 14-fold increase in xanthine dehydrogenase activity, which decreased with higher selenite concentrations (10(-5) M). The supplementation with 10(-7) M molybdate or tungstate was without effect. High concentrations of tungstate decreased the xanthine dehydrogenase if selenite was also present. In comparison, high concentrations of molybdate affected only a small decrease in activity level at the optimal concentration for selenite and relieved to some degree the inhibitory effect of 10(-5) M selenite. With hypoxanthine and xanthine as substrates for growth again only the addition of selenite was necessary to show a similar increase in xanthine dehydrogenase activity. C. acidiurici could be grown in a mineral medium. Both xanthine dehydrogenase and formate dehydrogenase exhibited the highest level of activity if selenite and tungstate were present in that medium. In C. cyclindrosporum the basal activity level of xanthine dehydrogenase was about 0.95 mumol/min x mg of protein. The addition of 10(-7) M selenite to the growth medium increased the activity level about 3-fold, but the highest level (3.7 U/mg) was reached if 10(-7) M molybdate was also added. The presence of tungstate resulted in a decreased enzyme activity.

Microbial metabolism of the pyridine ring. Formation of pyridinediols (dihydroxypyridines) as intermediates in the degradation of pyridine compounds by micro-organisms

1. Several species of micro-organisms that were capable of utilizing pyridine compounds as carbon and energy source were isolated from soil and sewage. Compounds degraded included pyridine and the three isomeric hydroxypyridines. 2. Suitable modifications of the cultural conditions led to the accumulation of pyridinediols (dihydroxypyridines), which were isolated and characterized. 3. Three species of Achromobacter produced pyridine-2,5-diol from 2- or 3-hydroxypyridine whereas an uncommon Agrobacterium sp. (N.C.I.B. 10413) produced pyridine-3,4-diol from 4-hydroxypyridine. 4. On the basis of chemical isolation, induction of the necessary enzymes in washed suspensions and the substrate specificity exhibited by the isolated bacteria, the initial transformations proposed are: 2-hydroxypyridine --> pyridine-2,5-diol; 3-hydroxypyridine --> pyridine-2,5-diol and 4-hydroxypyridine --> pyridine-3,4-diol. 5. A selected pyridine-utilizer, Nocardia Z1, did not produce any detectable hydroxy derivative from pyridine, but carried out a slow oxidation of 3-hydroxypyridine to pyridine-2,3-diol and pyridine-3,4-diol. These diols were not further metabolized. 6. Addition of the isomeric hydroxypyridines to a model hydroxylating system resulted in the formation of those diols predicted by theory.

Purification and properties of 2-furoyl-coenzyme A hydroxylase from Pseudomonas putida F2

1. 2-Furoyl-CoA hydroxylase of Pseudomonas putida F2 has been purified 60-fold by a combination of (NH(4))(2)SO(4) fractionation, DEAE-cellulose chromatography and agarose chromatography. 2. The purified enzyme catalyses the formation of 5-hydroxy-2-furoyl-CoA, which tautomerizes to form 5-oxo-Delta(2)-dihydro-2-furoyl-CoA. 3. The enzyme has a requirement for an electron acceptor that can be satisfied by a membrane preparation from 2-furoate-grown Ps. putida F2 or by artificial electron acceptors, and so presumably the incorporated oxygen atom is derived from water rather than molecular oxygen. 4. The enzyme is a large protein with a molecular weight of 3.27x10(6) and is disrupted to form inactive subunits in the presence of 0.2% (w/v) sodium dodecyl sulphate. It has a pH optimum of 8.5-9.5, a K(m) for 2-furoyl-CoA of 20.2mum and an absorption spectrum with a trough at 265nm and a single peak at 273nm. No absorption peaks are detectable in the visible region of the spectrum. 5. The enzyme is resistant to the effects of a wide range of potential inhibitors, but is inhibited by the copper-chelating agents bathocuproin and cuprizone, though not by sodium diethyldithiocarbamate. 6. Flavins are absent and the iron content does not show a sustained increase during purification. The copper content of the protein increases in close correlation with the increase in specific activity during purification. 7. A catalytic sequence for the hydroxylation of 2-furoyl-CoA by a copper protein is proposed.

The oxidation of nicotinic acid by Pseudomonas ovalis Chester. The terminal oxidase

In cell-free extracts of Pseudomonas ovalis nicotinic acid oxidase is confined to the wallmembrane fraction. It is associated with an electron-transport chain comprising b- and c-type cytochromes only, differing proportions of which are reduced by nicotinate and NADH. CO difference-spectra show two CO-binding pigments, cytochrome o (absorption maximum at 417nm) and another component absorbing maximally at 425nm. Cytochrome o is not reduced by NADH or by succinate but is by nicotinate, which can also reduce the ;425' CO-binding pigment. The effects of inhibitors of terminal oxidation support the idea of two terminal oxidases and a scheme involving the ;425' CO-binding pigment and the other components of the electron-transport chain is proposed.

The bacterial oxidation of picolinamide, a photolytic product of Diquat

The pathway of oxidation of picolinamide (pyridine-2-carboxamide) by a Gram-negative rod has been elucidated. Under conditions of high pH, restricted aeration and high substrate concentration, whole cells released 2,5-dihydroxypyridine into culture supernatants. Sodium arsenite at 5mm caused whole cells to accumulate 6-hydroxypicolinate, and, at 1mm, pyruvate, in culture media. Whole cells oxidized picolinamide, picolinate, 6-hydroxypicolinate, maleamate and maleate without lag. Cell-free extracts converted picolinamide into picolinate, and hydroxylated picolinate to 6-hydroxypicolinate. The hydroxylase was particulate, but could be solubilized by ultrasonic treatment; it required NAD(+) for activity, and did not require molecular oxygen. 2,5-Dihydroxypyridine was converted into maleamate and formate by an oxygenase requiring GSH and Fe(2+). Maleamate was deamidated to maleate, and maleate isomerized to fumarate, by unsupplemented extracts.

The metabolism of 2-furoic acid by Pseudomanas F2

1. Pseudomonas F2 isolated by enrichment culture on 2-furoic acid and grown with it as carbon source oxidized the compound with a Q(o) (2) of 170mul./mg. dry wt./hr. and the overall consumption of 2.5mumoles of oxygen/mumole of substrate. 2. In the presence of 1mm-sodium arsenite, oxygen uptake was restricted to 0.54mumole/mumole of 2-furoate oxidized, with the formation of 0.86mumole of 2-oxoglutarate/mumole of 2-furoate. 3. Cell suspensions, disrupted in a French pressure cell and centrifuged at 27000g, yielded supernatants capable of catalysing the slow oxidation of 2-furoate (0.17mumole/mg. of protein/hr.). 4. Fractionation of 27000g supernatants at 200000g yielded a soluble enzyme fraction capable of catalysing the oxidation of 2-furoate only in the presence of added 200000g pellet or of Methylene Blue. 5. The 2-furoate-stimulated uptake of oxygen or the anaerobic reduction of Methylene Blue by dialysed 27000g supernatant required the addition of ATP and CoA, and the rate of oxygen uptake was further enhanced by the addition of magnesium chloride and NAD(+). 6. The role of ATP and CoA in the formation of 2-furoyl-CoA was demonstrated by the accumulation of 2-furoylhydroxamic acid in the presence of hydroxylamine. 7. Dialysed 200000g supernatant, treated with Dowex 1, required the addition of ATP, CoA and Methylene Blue before it could oxidize 2-furoate to 2-oxoglutarate, which was trapped in unitary stoicheiometric yield as its phenylhydrazone. Magnesium chloride and NAD(+) were not stimulatory in this system. The oxidation of 2-furoate to 2-oxoglutarate was not inhibited by substrate analogues, metal ion-chelating agents, thiol-active compounds or inhibitors of cytochrome-mediated electron transport. 8. No evidence was obtained for the intervention of 2,5-dioxovalerate as an intermediate in 2-oxoglutarate formation.