Purification and properties of 4-halobenzoate-coenzyme A ligase from Pseudomonas sp. CBS3

Epoxy Coenzyme A Thioester pathways for degradation of aromatic compounds

Aromatic compounds (biogenic and anthropogenic) are abundant in the biosphere. Some of them are well-known environmental pollutants. Although the aromatic nucleus is relatively recalcitrant, microorganisms have developed various catabolic routes that enable complete biodegradation of aromatic compounds. The adopted degradation pathways depend on the availability of oxygen. Under oxic conditions, microorganisms utilize oxygen as a cosubstrate to activate and cleave the aromatic ring. In contrast, under anoxic conditions, the aromatic compounds are transformed to coenzyme A (CoA) thioesters followed by energy-consuming reduction of the ring. Eventually, the dearomatized ring is opened via a hydrolytic mechanism. Recently, novel catabolic pathways for the aerobic degradation of aromatic compounds were elucidated that differ significantly from the established catabolic routes. The new pathways were investigated in detail for the aerobic bacterial degradation of benzoate and phenylacetate. In both cases, the pathway is initiated by transforming the substrate to a CoA thioester and all the intermediates are bound by CoA. The subsequent reactions involve epoxidation of the aromatic ring followed by hydrolytic ring cleavage. Here we discuss the novel pathways, with a particular focus on their unique features and occurrence as well as ecological significance.

Aerobic degradation of polychlorinated biphenyls

The microbial degradation of polychlorinated biphenyls (PCBs) has been extensively studied in recent years. The genetic organization of biphenyl catabolic genes has been elucidated in various groups of microorganisms, their structures have been analyzed with respect to their evolutionary relationships, and new information on mobile elements has become available. Key enzymes, specifically biphenyl 2,3-dioxygenases, have been intensively characterized, structure/sequence relationships have been determined and enzymes optimized for PCB transformation. However, due to the complex metabolic network responsible for PCB degradation, optimizing degradation by single bacterial species is necessarily limited. As PCBs are usually not mineralized by biphenyl-degrading organisms, and cometabolism can result in the formation of toxic metabolites, the degradation of chlorobenzoates has received special attention. A broad set of bacterial strategies to degrade chlorobenzoates has recently been elucidated, including new pathways for the degradation of chlorocatechols as central intermediates of various chloroaromatic catabolic pathways. To optimize PCB degradation in the environment beyond these metabolic limitations, enhancing degradation in the rhizosphere has been suggested, in addition to the application of surfactants to overcome bioavailability barriers. However, further research is necessary to understand the complex interactions between soil/sediment, pollutant, surfactant and microorganisms in different environments.

Biochemical and molecular characterization of phenylacetate-coenzyme A ligase, an enzyme catalyzing the first step in aerobic metabolism of phenylacetic acid in Azoarcus evansii

Phenylacetate-coenzyme A ligase (PA-CoA ligase; AMP forming, EC 6.2. 1.30), the enzyme catalyzing the first step in the aerobic degradation of phenylacetate (PA) in Azoarcus evansii, has been purified and characterized. The gene (paaK) coding for this enzyme was cloned and sequenced. The enzyme catalyzes the reaction of PA with CoA and MgATP to yield phenylacetyl-CoA (PACoA) plus AMP plus PPi. The enzyme was specifically induced after aerobic growth in a chemically defined medium containing PA or phenylalanine (Phe) as the sole carbon source. Growth with 4-hydroxyphenylacetate, benzoate, adipate, or acetate did not induce the synthesis of this enzyme. This enzymatic activity was detected very early in the exponential phase of growth, and a maximal specific activity of 76 nmol min(-1) mg of cell protein(-1) was measured. After 117-fold purification to homogeneity, a specific activity of 48 micromol min(-1) mg of protein(-1) was achieved with a turnover number (catalytic constant) of 40 s(-1). The protein is a monomer of 52 kDa and shows high specificity towards PA; other aromatic or aliphatic acids were not used as substrates. The apparent K(m) values for PA, ATP, and CoA were 14, 60, and 45 microM, respectively. The PA-CoA ligase has an optimum pH of 8 to 8.5 and a pI of 6.3. The enzyme is labile and requires the presence of glycerol for stabilization. The N-terminal amino acid sequence of the purified protein showed no homology with other reported PA-CoA ligases. The gene encoding this enzyme is 1, 320 bp long and codes for a protein of 48.75 kDa (440 amino acids) which shows high similarity with other reported PA-CoA ligases. An amino acid consensus for an AMP binding motif (VX2SSGTTGXP) was identified. The biochemical and molecular characteristics of this enzyme are quite different from those of the isoenzyme catalyzing the same reaction under anaerobic conditions in the same bacterium.

Transformation of the ionic X-ray contrast agent diatrizoate and related triiodinated benzoates by Trametes versicolor

Iodinated X-ray contrast agents are considered to be nondegradable by microorganisms. The decomposition of the ionic X-ray contrast agents Diatrizoate (3,5-di(acetamido)-2,4,6-triiodobenzoic acid) and Iodipamide (3,3'-adipoyl-diimino-di(2,4,6-triiodobenzoic acid) and related triiodinated benzoates (Acetrizoate [3-acetylamino-2,4, 6-triiodobenzoic acid] and Aminotrizoate [3-amino-2,4, 6-triiodobenzoic acid]) by Trametes versicolor has been investigated. The fungus was able to transform all tested triiodinated benzoates cometabolically. During transformation of these compounds, iodide was released, but deiodination was not complete. T. versicolor liberated traces of 14CO2 from uniformly ring-14C-labeled Diatrizoate (3,5-di(acetamido)-2,4,6-triiodobenzoate). Various extracellular metabolites were detected during transformation of the different substances. In the transformation of Diatrizoate, the three main metabolites were identified as 3,5-di(acetamido)-2, 6-diiodobenzoic acid, 3,5-di(acetamido)-2,4-diiodobenzoic acid, and 3,5-di(acetamido)-2-iodobenzoic acid, suggesting reductive deiodinations in steps as initial transformation steps.

Purification and characterization of 2,6-dichloro-p-hydroquinone chlorohydrolase from Flavobacterium sp. strain ATCC 39723

The biochemistry of pentachlorophenol (PCP) degradation by Flavobacterium sp. strain ATCC 39723 has been studied, and two enzymes responsible for the conversion of PCP to 2,6-dichloro-p-hydroquinone (2,6-DiCH) have previously been purified and characterized. In this study, enzymatic activities consuming 2,6-DiCH were identified from the cell extracts of strain ATCC 39723. The enzyme was purified to apparent homogeneity by a purification scheme consisting of seven steps. Gel filtration chromatography showed a native molecular weight of about 40,000, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single protein of 42,500 Da. The purified enzyme converted 2,6-DiCH to 6-chlorohydroxyquinol (6-chloro-1,2,4-trihydroxybenzene), which was easily oxidized by molecular oxygen and hard to detect. The end product, 6-chlorohydroxyquinol, was detected only in the presence of a reductase and NADH in the reaction mixture. The enzyme dechlorinated 2,6-DiCH but not 2,5-DiCH. The enzyme required Fe2+ for activity and was severely inhibited by metal chelating agents. The optimal conditions for activity were pH 7.0 and 40 degrees C. The Kcat for 2,6-DiCH was 35 microM, and the kcat was 0.011 s-1.

Anaerobic metabolism of aromatic compounds

Aromatic compounds comprise a wide variety of low-molecular-mass natural compounds (amino acids, quinones, flavonoids, etc.) and biopolymers (lignin, melanin). They are almost exclusively degraded by microorganisms. Aerobic aromatic metabolism is characterised by the extensive use of molecular oxygen. Monoxygenases and dioxygenases are essential for the hydroxylation and cleavage of aromatic ring structures. Accordingly, the characteristic central intermediates of the aerobic pathways (e.g. catechol) are readily attacked oxidatively. Anaerobic aromatic catabolism requires, of necessity, a quite different strategy. The basic features of this metabolism have emerged from studies on bacteria that degrade soluble aromatic substrates to CO2 in the complete absence of molecular oxygen. Essential to anaerobic aromatic metabolism is the replacement of all the oxygen-dependent steps by an alternative set of novel reactions and the formation of different central intermediates (e.g. benzoyl-CoA) for breaking the aromaticity and cleaving the ring; notably, in anaerobic pathways, the aromatic ring is reduced rather than oxidised. The two-electron reduction of benzoyl-CoA to a cyclic diene requires the cleavage of two molecules of ATP to ADP and P1 and is catalysed by benzoyl-CoA reductase. After nitrogenase, this is the second enzyme known which overcomes the high activation energy required for reduction of a chemically stable bond by coupling electron transfer to the hydrolysis of ATP. The alicyclic product cyclohex-1,5-diene-1-carboxyl-CoA is oxidised to acetyl-CoA via a modified beta-oxidation pathway; the ring structure is opened hydrolytically. Some phenolic compounds are anaerobically transformed to resorcinol (1,3-dihydroxybenzene) or phloroglucinol (1,3,5-trihydroxybenzene). These intermediates are also first reduced and then as alicyclic products oxidised to acetyl-CoA. This review gives an outline of the anaerobic pathways which allow bacteria to utilize aromatics even in the absence of oxygen. We focus on previously unknown reactions and on the enzymes characteristic for such novel metabolism.

Determination of the chemical pathway for 4-chlorobenzoate:coenzyme A ligase catalysis

4-Chlorobenzoate:coenzyme A ligase (4-CBA:CoA ligase) catalyzes the first step of the 4-CBA degradation pathway of Pseudomonas sp. strain CBS3. In this reaction, 4-CBA-CoA thioester synthesis is coupled to ATP cleavage. The studies described in this paper examine the intermediacy of 4-chlorobenzoyl-adenosine 5'phosphate diester (4-CBA-AMP) in the ligase reaction. The 4-CBA-AMP adduct was isolated from the ligase reaction mixture generated from magnesium adenosine 5-triphosphate (MgATP) and 4-CBA in the absence of CoA. The structure of the 4-CBA-AMP was verified by 1H- 13C-, and 31P-nuclear magnetic resonance analysis. Single-turnover reactions carried out with 14C-labeled 4-CBA in a rapid quench apparatus demonstrated formation of the enzyme. 4-CBA-AMP.MgPPi complex from the enzyme.4-CBA.MgATP complex at a rate of 135 s-1. The rate of ligand release from the enzyme.4-CBA-AMP.MgPPi complex was measured at 0.013 s-1. Single-turnover reactions of [14C]-4-CBA, MgATP, and CoA catalyzed by the ligase revealed that the 4-CBA-AMP intermediate formed reaches a maximum level of 25% of the starting 4-CBA within 10 ms and then declines with the formation of the 4-CBA-CoA. The rates of the adenylation and thioesterification partial reactions, determined by kinetic simulation of the rate data, are nearly equal (135 and 100 s-1). Substitution of CoA with the slow substrate pantetheine did not significantly alter the rate of the adenylation step but did reduce the rate of the thioesterification step to 2 s-1. The maximum level of 4-CBA-AMP reached during the single-turnover reaction of 4-CBA, MgATP, and pantetheine corresponded to one-half of the starting 4-CBA.

Biosynthesis of halogenated metabolites by bacteria

Halogenated metabolites, originally thought to be infrequent in nature, are actually nothing unusual at all, and are produced by many different organisms, including bacteria. Whereas marine bacteria usually produce brominated compounds, terrestrial bacteria preferentially synthesize chlorometabolites, but fluoro- and iodometabolites can also be found. Haloperoxidases, enzymes capable of catalyzing the formation of carbon halogen bonds in the presence of hydrogen peroxide and halide ions (Cl-, Br- and I-) have been isolated and characterized from different bacteria. These enzymes turned out to be very unspecific and are obviously not the type of halogenating enzymes responsible for the formation of halometabolites in bacteria. A yet-unknown type of halogenating enzyme having both substrate and regio-specificity must be involved in the biosynthesis of halogenated compounds.

Coenzyme A ligases involved in anaerobic biodegradation of aromatic compounds

Bacterial strains and consortia of bacteria have been isolated for their ability to degrade, under anaerobic conditions, homocyclic monoaromatic compounds, such as phenolic compounds, methylbenzenes, and aminobenzenes. As opposed to aerobic conditions where these compounds are degraded via dihydroxyl intermediates introduced by oxygenases, most of aromatic compounds under anaerobic conditions are metabolized via aromatic acid intermediates, such as nitrobenzoates, hydroxybenzoates, or phenylacetate. These aromatic acids are then transformed to benzoate before the reduction and the cleavage of the benzene ring to aliphatic acid products. One step of these catabolic pathways is the addition of a coenzyme A (CoA) residue to the carboxylic group of the aromatic acids by CoA ligases. This addition would facilitate the enzymatic transformation of the aromatic acids to benzoyl-CoA and the subsequent degradation steps of this latter molecule. Aromatic acid-CoA ligases have been characterized or detected from several bacterial strains that were grown under anaerobic conditions and from an anaerobic syntrophic consortium. They are also involved in the degradation of some aromatic compounds under aerobic conditions. They have molecular masses varying between 48 and 61 kDa, require ATP, Mg2+, and CoASH as cofactors, and have an optimum pH of 8.2-9.3. Amino acid sequence analyses of four aromatic acid-CoA ligases have revealed that they are related to an AMP-binding protein family. Aromatic acid-CoA ligases expressed in anaerobically grown bacterial cells are strictly regulated by the anaerobic conditions and the presence of aromatic cells.

Dehalogenation of 4-chlorobenzoate. Characterisation of 4-chlorobenzoyl-coenzyme A dehalogenase from Pseudomonas sp. CBS3

Pseudomonas sp. CBS3 is capable of growing with 4-chlorobenzoate as sole source of carbon and energy. The removal of the chlorine of 4-chlorobenzoate is performed in the first degradation step by an enzyme system consisting of three proteins. A 4-halobenzoate-coenzyme A ligase activates 4-chlorobenzoate in a coenzyme A, ATP and Mg2+ dependent reaction to 4-chlorobenzoyl-coenzyme A. This thioester intermediate is dehalogenated by the 4-chlorobenzoyl-coenzyme A dehalogenase. Finally coenzyme A is split off by a 4-hydroxybenzoyl-CoA thioesterase to form 4-hydroxybenzoate. The involved 4-chlorobenzoyl-coenzyme A dehalogenase was purified to apparent homogeneity by a five-step purification procedure. The native enzyme had an apparent molecular mass of 120,000 and was composed of four identical polypeptide subunits of 31 kDa. The enzyme displayed an isoelectric point of 6.7. The maximal initial rate of catalysis was achieved at pH 10 at 60 degrees C. The apparent Km value for 4-chlorobenzoyl-coenzyme A was 2.4-2.7 microM. Vmax was 1.1 x 10(-7) M sec-1 (2.2 mumol min-1 mg-1 of protein). The NH2-terminal amino acid sequence was determined. All 4-halobenzoyl-coenzyme A thioesters, except 4-fluorobenzoyl-coenzyme A, were dehalogenated by the 4-chlorobenzoyl-CoA dehalogenase.

Benzoyl-coenzyme-A 3-monooxygenase, a flavin-dependent hydroxylase. Purification, some properties and its role in aerobic benzoate oxidation via gentisate in a denitrifying bacterium

A new variant of aerobic benzoate degradation has been found in a denitrifying bacterium in which benzoyl-CoA is the first intermediate [Altenschmidt, U., Oswald, B., Steiner, E., Herrmann, H. & Fuchs, G. (1993) New aerobic benzoate oxidation pathway via benzoyl-coenzyme A and 3-hydroxybenzoyl-coenzyme A in a denitrifying Pseudomonas sp, J. Bacteriol. 175, 4851-4858)]. The initial reaction is catalyzed by benzoate-CoA ligase (AMP-forming), converting benzoate into benzoyl-CoA. The next step is 3-hydroxylation of benzoyl-CoA to 3-hydroxybenzoyl-CoA catalyzed by a flavin-nucleotide-dependent monooxygenase, benzoyl-CoA 3-monooxygenase. This novel enzyme has been purified and studied. It is specific for NADPH and requires the presence of a flavin nucleotide for activity; both FAD or FMN function similarly well as cofactor. Only benzoyl-CoA, but not benzoate, is hydroxylated. The protein is a monomer of M(r) 65,000 and is induced when cells are grown aerobically with benzoate. 3-Hydroxybenzoyl-CoA is further hydroxylated para to the hydroxyl group affording 2,5-dihydroxybenzoate (gentisate). This reaction requires another monooxygenase, 3-hydroxybenzoyl-CoA 6-monooxygenase, which is unspecific specific with respect to the pyridine nucleotide. Cells contain a second 6-monooxygenase activity which acts on free 3-hydroxybenzoate. Based on these and other data, the outlines of the new aerobic benzoate pathway have been deduced. The proposed intermediates are benzoyl-CoA, 3-hydroxybenzoyl-CoA, gentisate, maleylpyruvate, fumarylpyruvate and fumarate plus pyruvate.

Bacterial dehalogenases: biochemistry, genetics, and biotechnological applications

This review is a survey of bacterial dehalogenases that catalyze the cleavage of halogen substituents from haloaromatics, haloalkanes, haloalcohols, and haloalkanoic acids. Concerning the enzymatic cleavage of the carbon-halogen bond, seven mechanisms of dehalogenation are known, namely, reductive, oxygenolytic, hydrolytic, and thiolytic dehalogenation; intramolecular nucleophilic displacement; dehydrohalogenation; and hydration. Spontaneous dehalogenation reactions may occur as a result of chemical decomposition of unstable primary products of an unassociated enzyme reaction, and fortuitous dehalogenation can result from the action of broad-specificity enzymes converting halogenated analogs of their natural substrate. Reductive dehalogenation either is catalyzed by a specific dehalogenase or may be mediated by free or enzyme-bound transition metal cofactors (porphyrins, corrins). Desulfomonile tiedjei DCB-1 couples energy conservation to a reductive dechlorination reaction. The biochemistry and genetics of oxygenolytic and hydrolytic haloaromatic dehalogenases are discussed. Concerning the haloalkanes, oxygenases, glutathione S-transferases, halidohydrolases, and dehydrohalogenases are involved in the dehalogenation of different haloalkane compounds. The epoxide-forming halohydrin hydrogen halide lyases form a distinct class of dehalogenases. The dehalogenation of alpha-halosubstituted alkanoic acids is catalyzed by halidohydrolases, which, according to their substrate and inhibitor specificity and mode of product formation, are placed into distinct mechanistic groups. beta-Halosubstituted alkanoic acids are dehalogenated by halidohydrolases acting on the coenzyme A ester of the beta-haloalkanoic acid. Microbial systems offer a versatile potential for biotechnological applications. Because of their enantiomer selectivity, some dehalogenases are used as industrial biocatalysts for the synthesis of chiral compounds. The application of dehalogenases or bacterial strains in environmental protection technologies is discussed in detail.

On the origins and functions of the enzymes of the 4-chlorobenzoate to 4-hydroxybenzoate converting pathway

This review examines the enzymes of 4-chlorobenzoate to 4-hydroxybenzoate converting pathway found in certain soil bacteria. This pathway consists of three enzymes: 4-chlorobenzoate: Coenzyme A ligase, 4-chlorobenzoyl-Coenzyme A dehalogenase and 4-hydroxybenzoyl-Coenzyme A thioesterase. Recent progress made in the cloning and expression of the pathway genes from assorted bacterial strains is described. Gene order and sequence found among these strains are compared to reveal independent enzyme recruitment strategies. Sequence alignments made between the Pseudomonas sp. strain CBS3 4-chlorobenzoate pathway enzymes and structurally related proteins contained within the protein sequence data banks suggest possible origins in preexisting beta-oxidation pathways. The purification and characterization of the physical and kinetic properties of the pathway enzymes are described. Where possible a comparison of these properties between like enzymes from different bacterial sources are made.

Catabolism of aromatics in Pseudomonas putida U. Formal evidence that phenylacetic acid and 4-hydroxyphenylacetic acid are catabolized by two unrelated pathways

Phenylacetic acid (PhAcOH) and 4-hydroxyphenylacetic acid (4HOPhAcOH) are catabolized in Pseudomonas putida U through two different pathways. Mutation carried out with the transposon Tn5 has allowed the isolation of several mutants which, unlike the parental strain, are unable to grow in chemically defined medium containing either PhAcOH or 4HOPhAcOH as the sole carbon source. Analysis of these strains showed that the ten mutants unable to grow in PhAcOH medium grew well in the one containing 4HOPhAcOH, whereas four mutants handicapped in the degradation of 4HOPhAcOH were all able to utilize PhAcOH. These results show that the degradation of these two aromatic compounds in P. putida U is not carried out as formerly believed through a single linear and common pathway, but by two unrelated routes. Identification of the blocked point in the catabolic pathway and analysis of the intermediate accumulated, showed that the mutants unable to utilize 4HOPhAcOH corresponded to two different groups: those blocked in the gene encoding 4-hydroxyphenylacetic acid-3-hydroxylase; and those blocked in the gene encoding homoprotocatechuate-2,3-dioxygenase. Mutants unable to use PhAcOH as the sole carbon source have been also classified into two different groups: those which contain a functional PhAc-CoA ligase protein; and those lacking this enzyme activity.

The bacterial degradation of benzoic acid and benzenoid compounds under anaerobic conditions: unifying trends and new perspectives

Simple homocyclic aromatic compounds are extremely abundant in the environment and are derived largely from lignin. Such compounds may enter anaerobic environments and several groups of bacteria, exhibiting diverse energy-yielding mechanisms, have evolved the capacity to overcome the thermodynamic stability of the benzene nucleus and degrade aromatic compounds under these conditions. Over the last few years considerable advances have been made in our understanding of the biochemical strategies underlying the bacterial degradation of aromatic compounds in anoxic environments. The study of the biochemistry, and more recently the molecular genetics of the photosynthetic bacterium Rhodopseudomonas palustris and several strains of denitrifying pseudomonads, has provided the greatest insight into the mechanism and regulation of aromatic degradation under anaerobic conditions. Research has centred around the anaerobic degradation of benzoic acid. This involves the initial activation to form benzoyl-Coenzyme A, reduction of the aromatic nucleus--a reaction that has only recently been demonstrated in vitro--and the subsequent degradation of the alicyclic intermediates. Recently, much information regarding the exact nature of these intermediates has been obtained. Also through recent studies, it has become increasingly clear that benzoyl-CoA is a central metabolic intermediate during the anaerobic degradation of structurally diverse aromatic compounds. The initial metabolism of these compounds involves the formation of a carboxyl group on the aromatic nucleus (if necessary) and the synthesis of the respective Coenzyme A thioester; this results in the direct formation of benzoyl-Coenzyme A rather than benzoate. In many cases of anaerobic aromatic degradation studied in batch culture, aromatic intermediates are transiently excreted into the medium. It is argued that the study of this phenomenon may facilitate the understanding of the regulation and kinetics of the aromatic degradative pathways.

4-Hydroxybenzoate-coenzyme A ligase from Rhodopseudomonas palustris: purification, gene sequence, and role in anaerobic degradation

Anaerobic metabolism of most aromatic acids is initiated by coenzyme A thioester formation. Rhodopseudomonas palustris grows well under anaerobic, phototrophic conditions with many aromatic acids, including benzoate and 4-hydroxybenzoate, as a carbon source. A coenzyme A ligase that reacts with 4-hydroxybenzoate was purified from 4-hydroxybenzoate-grown cells of R. palustris. This enzyme required MgATP, reduced coenzyme A, and 4-hydroxybenzoate, benzoate, or cyclohex-1,4-dienecarboxylate for optimal activity but also used phosphopantetheine, cyclohex-2,5-dienecarboxylate, and 4-fluorobenzoate at lower rates. The 4-hydroxybenzoate-coenzyme A ligase differed in molecular characteristics from a previously described benzoate-coenzyme A ligase from R. palustris, and the two ligases did not cross-react immunologically. The gene encoding the 4-hydroxybenzoate enzyme was cloned and sequenced. The deduced gene product showed about 20% amino acid identity with bacterial coenzyme A ligases involved in aerobic degradation of aromatic acids. An R. palustris mutant carrying a disrupted 4-hydroxybenzoate-coenzyme A ligase gene was unable to grow with 4-hydroxybenzoate under anaerobic conditions, indicating that the enzyme is essential for anaerobic degradation of this compound.

New aerobic benzoate oxidation pathway via benzoyl-coenzyme A and 3-hydroxybenzoyl-coenzyme A in a denitrifying Pseudomonas sp

A denitrifying Pseudomonas sp. is able to oxidize aromatic compounds compounds completely to CO2, both aerobically and anaerobically. It is shown that benzoate is aerobically oxidized by a new degradation pathway via benzoyl-coenzyme A (CoA) and 3-hydroxybenzoyl-CoA. The organism grew aerobically with benzoate, 3-hydroxybenzoate, and gentisate; catechol, 2-hydroxybenzoate, and protocatechuate were not used, and 4-hydroxybenzoate was a poor substrate. Mutants were obtained which were not able to utilize benzoate as the sole carbon source aerobically but still used 3-hydroxybenzoate or gentisate. Simultaneous adaptation experiments with whole cells seemingly suggested a sequential induction of enzymes of a benzoate oxidation pathway via 3-hydroxybenzoate and gentisate. Cells grown aerobically with benzoate contained a benzoate-CoA ligase (AMP forming) (0.1 mumol min-1 mg-1) which converted benzoate but not 3-hydroxybenzoate into its CoA thioester. The enzyme of 130 kDa composed of two identical subunits of 56 kDa was purified and characterized. Cells grown aerobically with 3-hydroxybenzoate contained a similarly active CoA ligase for 3-hydroxybenzoate, 3-hydroxybenzoate-CoA ligase (AMP forming). Extracts from cells grown aerobically with benzoate catalyzed a benzoyl-CoA- and flavin adenine dinucleotide-dependent oxidation of NADPH with a specific activity of at least 25 nmol NADPH oxidized min-1 mg of protein-1; NADH and benzoate were not used. This new enzyme, benzoyl-CoA 3-monooxygenase, was specifically induced during aerobic growth with benzoate and converted [U-14C]benzoyl-CoA stoichiometrically to [14C]3-hydroxybenzoyl-CoA.

Enzymes of anaerobic metabolism of phenolic compounds. 4-Hydroxybenzoate-CoA ligase from a denitrifying Pseudomonas species

The initial step of anaerobic 4-hydroxybenzoate and 3-hydroxybenzoate degradation was studied in a denitrifying Pseudomonas sp. 4'-Hydroxybenzoate and 3-hydroxybenzoate are converted into their coenzyme A (CoA) thioesters by two different specific coenzyme A ligases. 4-Hydroxybenzoate-CoA ligase (AMP-forming) was purified 350-fold. The ligase is active as a monomer of molecular mass 48 kDa, as determined by gel filtration and SDS/PAGE. At a pH optimum of 8.5, the apparent Km values for 4-hydroxybenzoate, ATP, and coenzyme A are 37 microM, 77 microM, and 125 microM, respectively. The enzyme reacts specifically with 4-hydroxybenzoate (100%) and 4-aminobenzoate (30%). Other analogues of benzoate, notably 3- or 2-hydroxybenzoate, are inactive, and 2,4-dihydroxybenzoate and 2-hydroxy-4-methylbenzoate act as competitive inhibitors (Ki = 1 microM). Polyclonal antibodies were raised and used in immunoblot assays to study the regulation of the expression of 4-hydroxybenzoate-CoA ligase. The ligase is synthesized when cells are grown anaerobically with 4-hydroxybenzoate, phenol, or p-cresol; phenol and p-cresol are degraded via 4-hydroxybenzoate. The enzyme is not present in cells grown aerobically with 4-hydroxybenzoate or anaerobically with benzoate or 4-hydroxyphenylacetate.