RESUMEN
The Sporomusa genus comprises anaerobic spore-forming acetogenic bacteria that stain Gram-negative. Sporomusa species typically grow with one-carbon substrates and N-methylated compounds. In the degradation of these compounds methyltransferases are involved. In addition, Sporomusa species can grow autotrophically with H2 and CO2 , and use a variety of sugars for acetogenic growth. Here we describe a genome analysis of Sporomusa strain An4 and a proteome analysis of cells grown under five different conditions. Comparison of the genomes of Sporomusa strain An4 and Sporomusa ovata strain H1 indicated that An4 is a S. ovata strain. Proteome analysis showed a high abundance of several methyltransferases, predominantly trimethylamine methyltransferases, during growth with betaine, whereas trimethylamine is one of the main end-products of betaine degradation. In methanol degradation methyltransferases are also involved. In methanol-utilizing methanogens, two methyltransferases catalyse methanol conversion, methyltransferase 1 composed of subunits MtaB and MtaC and methyltransferase 2, also called MtaA. The two methyltransferase 1 subunits MtaB and MtaC were highly abundant when strain An4 was grown with methanol. However, instead of MtaA a methyltetrahydrofolate methyltransferase was synthesized. We propose a novel methanol degradation pathway in Sporomusa strain An4 that uses a methyltetrahydrofolate methyltransferase instead of MtaA.
Asunto(s)
Proteoma , Veillonellaceae/metabolismo , Betaína/metabolismo , Carbono/metabolismo , Genoma Bacteriano , Metanol/metabolismo , Metilaminas/metabolismo , Metiltransferasas/metabolismo , Veillonellaceae/enzimología , Veillonellaceae/genéticaRESUMEN
Following the isolation, cultivation and characterization of the rumen bacterium Anaerovibrio lipolyticus in the 1960s, it has been recognized as one of the major species involved in lipid hydrolysis in ruminant animals. However, there has been limited characterization of the lipases from the bacterium, despite the importance of understanding lipolysis and its impact on subsequent biohydrogenation of polyunsaturated fatty acids by rumen microbes. This study describes the draft genome of Anaerovibrio lipolytica 5ST, and the characterization of three lipolytic genes and their translated protein. The uncompleted draft genome was 2.83 Mbp and comprised of 2,673 coding sequences with a G+C content of 43.3%. Three putative lipase genes, alipA, alipB and alipC, encoding 492-, 438- and 248- amino acid peptides respectively, were identified using RAST. Phylogenetic analysis indicated that alipA and alipB clustered with the GDSL/SGNH family II, and alipC clustered with lipolytic enzymes from family V. Subsequent expression and purification of the enzymes showed that they were thermally unstable and had higher activities at neutral to alkaline pH. Substrate specificity assays indicated that the enzymes had higher hydrolytic activity against caprylate (C8), laurate (C12) and myristate (C14).
Asunto(s)
Lipasa/genética , Lipasa/metabolismo , Veillonellaceae/enzimología , Veillonellaceae/genética , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Animales , Secuencia Conservada , Activación Enzimática , Expresión Génica , Concentración de Iones de Hidrógeno , Lipasa/química , Lipasa/aislamiento & purificación , Lipólisis , Datos de Secuencia Molecular , Filogenia , Proteínas Recombinantes/genética , Proteínas Recombinantes/aislamiento & purificación , Proteínas Recombinantes/metabolismo , Alineación de Secuencia , Especificidad por Sustrato , Temperatura , Veillonellaceae/clasificaciónRESUMEN
The hydrolysis of free fatty acids from lipids is a prerequisite for biohydrogenation, a process that effectively saturates free fatty acids. Anaerovibrio lipolyticus 5s and Butyrivibrio fibrisolvens have long been thought to be the major contributors to ruminal lipolysis; however, Propionibacterium avidum and acnes recently have been identified as contributing lipase activity in the rumen. In order to further characterize the lipase activity of these bacterial populations, each was grown with three different lipid substrates, olive oil, corn oil, and flaxseed oil (3 %). Because different finishing rations contain varying levels of glycogen (a source of free glucose) this study also documented the effects of glucose on lipolysis. P. avidum and A. lipolyticus 5s demonstrated the most rapid rates (P < 0.05) of lipolysis for cultures grown with olive oil and flaxseed oil, respectively. A. lipolyticus, B. fibrisolvens, and P. avidum more effectively hydrolyzed flaxseed oil than olive oil or corn oil, especially in the presence of 0.02 % glucose. Conversely, P. acnes hydrolyzed corn oil more readily than olive oil or flaxseed oil and glucose had no effect on lipolytic rate. Thus, these bacterial species demonstrated different specificities for oil substrates and different sensitivities to glucose.
Asunto(s)
Butyrivibrio/enzimología , Glucosa/metabolismo , Lipasa/metabolismo , Aceites de Plantas/metabolismo , Propionibacterium/enzimología , Rumen/microbiología , Veillonellaceae/enzimología , Animales , Butyrivibrio/efectos de los fármacos , Butyrivibrio/crecimiento & desarrollo , Bovinos , Aceite de Maíz/metabolismo , Medios de Cultivo , Glucosa/farmacología , Aceite de Linaza/metabolismo , Lipólisis/efectos de los fármacos , Aceite de Oliva , Propionibacterium/efectos de los fármacos , Propionibacterium/crecimiento & desarrollo , Rumen/efectos de los fármacos , Especificidad por Sustrato , Veillonellaceae/efectos de los fármacos , Veillonellaceae/crecimiento & desarrolloRESUMEN
Cobamides (Cbas) are cobalt (Co) containing tetrapyrrole-derivatives involved in enzyme-catalyzed carbon skeleton rearrangements, methyl-group transfers, and reductive dehalogenation. The biosynthesis of cobamides is complex and is only performed by some bacteria and achaea. Cobamides have an upper (Coß) ligand (5'-deoxyadenosyl or methyl) and a lower (Coα) ligand base that contribute to the axial Co coordinations. The identity of the lower Coα ligand varies depending on the organism synthesizing the Cbas. The homoacetogenic bacterium Sporomusa ovata synthesizes two unique phenolic cobamides (i.e., Coα-(phenolyl/p-cresolyl)cobamide), which are used in the catabolism of methanol and 3,4-dimethoxybenzoate by this bacterium. The S. ovata ArsAB enzyme activates a phenolic lower ligand prior to its incorporation into the cobamide. ArsAB consists of two subunits, both of which are homologous (â¼35% identity) to the well-characterized Salmonella enterica CobT enzyme, which transfers nitrogenous bases such as 5,6-dimethylbenzimidazole (DMB) and adenine, but cannot utilize phenolics. Here we report the three-dimensional structure of ArsAB, which shows that the enzyme forms a pseudosymmetric heterodimer, provide evidence that only the ArsA subunit has base:phosphoribosyl-transferase activity, and propose a mechanism by which phenolic transfer is facilitated by an activated water molecule.
Asunto(s)
Cresoles/metabolismo , Pentosiltransferasa/química , Pentosiltransferasa/metabolismo , Fenol/metabolismo , Veillonellaceae/enzimología , Cristalografía por Rayos X , Modelos Moleculares , Conformación Proteica , Multimerización de Proteína , Subunidades de Proteína/química , Subunidades de Proteína/metabolismo , Veillonellaceae/químicaRESUMEN
In the homoacetogenic bacterium Sporomusa ovata, phenol and p-cresol are converted into α-ribotides, which are incorporated into biologically active cobamides (Cbas) whose lower ligand bases do not form axial co-ordination bonds with the cobalt ion of the corrin ring. Here we report the identity of two S. ovata genes that encode an enzyme that transfers the phosphoribosyl group of nicotinate mononucleotide (NaMN) to phenol or p-cresol, yielding α-O-glycosidic ribotides. The alluded genes were named arsA and arsB (for alpha-ribotide synthesis), arsA and arsB were isolated from a genomic DNA library of S. ovata. A positive selection strategy using an Escherichia coli strain devoid of NaMN:5,6-dimethylbenzimidazole (DMB) phosphoribosyltransferase (CobT) activity was used to isolate a fragment of S. ovata DNA that contained arsA and arsB, whose nucleotide sequences overlapped by 8 bp. SoArsAB was isolated to homogeneity, shown to be functional as a heterodimer, and to have highest activity at pH 9. SoArsAB also activated DMB to its α-N-glycosidic ribotide. Previously characterized CobT-like enzymes activate DMB but do not activate phenolics. NMR spectroscopy was used to confirm the incorporation of phenol into the cobamide, and mass spectrometry was used to identify SoArsAB reaction products.
Asunto(s)
Cobamidas/metabolismo , Enzimas/genética , Enzimas/metabolismo , Fenoles/metabolismo , Veillonellaceae/enzimología , Secuencia de Aminoácidos , Vías Biosintéticas , ADN Bacteriano/química , ADN Bacteriano/genética , Enzimas/aislamiento & purificación , Escherichia coli/genética , Biblioteca de Genes , Prueba de Complementación Genética , Concentración de Iones de Hidrógeno , Cinética , Datos de Secuencia Molecular , Estructura Molecular , Mononucleótido de Nicotinamida/análogos & derivados , Mononucleótido de Nicotinamida/metabolismo , Multimerización de Proteína , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Veillonellaceae/genéticaRESUMEN
A mesophilic bacterium, strain An4, was isolated from an underground gas storage reservoir with methanol as substrate and perchlorate as electron acceptor. Cells were Gram-negative, spore-forming, straight to curved rods, 0.5-0.8 microm in diameter, and 2-8 microm in length, growing as single cells or in pairs. The cells grew optimally at 37 degrees C, and the pH optimum was around 7. Strain An4 converted various alcohols, organic acids, fructose, acetoin, and H(2)/CO(2) to acetate, usually as the only product. Succinate was decarboxylated to propionate. The isolate was able to respire with (per)chlorate, nitrate, and CO(2). The G+C content of the DNA was 42.6 mol%. Based on the 16S rRNA gene sequence analysis, strain An4 was most closely related to Sporomusa ovata (98% similarity). The bacterium reduced perchlorate and chlorate completely to chloride. Key enzymes, perchlorate reductase and chlorite dismutase, were detected in cell-free extracts.
Asunto(s)
Cloratos/metabolismo , Combustibles Fósiles/microbiología , Percloratos/metabolismo , Veillonellaceae/fisiología , Datos de Secuencia Molecular , Oxidorreductasas/metabolismo , Filogenia , Veillonellaceae/clasificación , Veillonellaceae/enzimología , Veillonellaceae/aislamiento & purificaciónRESUMEN
Two novel lipase genes RlipE1 and RlipE2 which encoded 361- and 265-amino acid peptides, respectively, were recovered from a metagenomic library of the rumen microbiota of Chinese Holstein cows. A BLAST search revealed a high similarity (90%) between RlipE2 and a carboxylesterase from Thermosinus carboxydivorans Nor1, while there was a low similarity (below 50%) between RlipE1 and other lipases. Phylogenetic analysis indicated that RlipE2 clustered with the lipolytic enzymes from family V while RlipE1 clustered with six other putative bacterial lipases which might constitute a new subfamily. The recombinant lipases were thermally unstable and retained 60% activity over a pH range of 6.5-8.5. Substrate specificity assay indicated that both enzymes had higher hydrolytic activity toward laurate (C(12)), palmitate (C(16)) and stearate (C(18)). The novel phylogenetic affiliation and high specificity of both enzymes for long-chain fatty acid make them interesting targets for manipulation of rumen lipid metabolism.
Asunto(s)
Lipasa/metabolismo , Rumen/microbiología , Veillonellaceae/enzimología , Secuencia de Aminoácidos , Animales , Bovinos , Ácidos Grasos/metabolismo , Femenino , Biblioteca de Genes , Genómica , Lipasa/clasificación , Lipasa/genética , Lipasa/aislamiento & purificación , Datos de Secuencia Molecular , FilogeniaRESUMEN
Mitsuokella multacida expresses a unique inositol polyphosphatase (PhyAmm) that is composed of tandem repeats (TRs). Each repeat possesses a protein tyrosine phosphatase (PTP) active-site signature sequence and fold. Using a combination of structural, mutational, and kinetic studies, we show that the N-terminal (D1) and C-terminal (D2) active sites of the TR have diverged and possess significantly different specificities for inositol polyphosphate. Structural analysis and molecular docking calculations identify steric and electrostatic differences within the substrate binding pocket of each TR that may be involved in the altered substrate specificity. The implications of our results for the biological function of related PTP-like phytases are discussed. Finally, the structures and activities of PhyAmm and tandemly repeated receptor PTPs are compared and discussed. To our knowledge, this is the first example of an inositol phosphatase with tandem PTP domains possessing substrate specificity for different inositol phosphates.
Asunto(s)
Proteínas Bacterianas/química , Proteínas Bacterianas/metabolismo , Monoéster Fosfórico Hidrolasas/química , Monoéster Fosfórico Hidrolasas/metabolismo , Veillonellaceae/enzimología , Veillonellaceae/genética , Secuencia de Aminoácidos , Proteínas Bacterianas/genética , Dominio Catalítico , Cristalografía por Rayos X/métodos , Análisis Mutacional de ADN , Cinética , Modelos Moleculares , Datos de Secuencia Molecular , Monoéster Fosfórico Hidrolasas/genética , Estructura Terciaria de Proteína , Alineación de Secuencia , Especificidad por Sustrato , Secuencias Repetidas en TándemRESUMEN
Histamine is an inflammatory agent that contributes to bovine laminitis. Cattle fed silage-containing rations often have large populations of Allisonella histaminiformans, but this obligate histidine-decarboxylating bacterium could not be isolated from cattle fed timothy hay. The growth of A. histaminiformans was stimulated by yeast extract, protein hydrolysates, and water-soluble extracts of alfalfa or corn silage. Extracts of alfalfa were more potent than corn silage. Because growth and histamine production were not stimulated by Casamino Acids or a mixture of purified amino acids, it appeared that A. histaminiformans requires peptides. The idea that A. histaminiformans requires peptides is consistent with the observation that alfalfa silages often have a large amount of peptide nitrogen.
Asunto(s)
Histamina/biosíntesis , Histidina Descarboxilasa/metabolismo , Histidina/metabolismo , Rumen/microbiología , Ensilaje/microbiología , Veillonellaceae/metabolismo , Alimentación Animal/microbiología , Animales , Bovinos , Medios de Cultivo , Medicago sativa/metabolismo , Veillonellaceae/enzimología , Zea mays/metabolismoRESUMEN
The GATC-specific restriction and modification activities were analyzed in 11 major bacterial representatives of ruminal microflora. Modification phenotype was observed in 13 out of 40 ruminal strains. MboI isoschizomeric restriction endonucleases were detected in 10 bacterial strains tested; three strains lacked any detectable corresponding endonuclease activity. The only examined strain of Mitsuokella multi-acida was found to possess a different type of endonuclease activity. This is the first report on restriction activity in ruminal treponemes M. multiacida and Megasphaera elsdenii.
Asunto(s)
Bacterias/enzimología , Enzimas de Restricción-Modificación del ADN/metabolismo , Rumen/microbiología , Animales , Bacterias/aislamiento & purificación , ADN Viral/metabolismo , Desoxirribonucleasas de Localización Especificada Tipo II/metabolismo , Electroforesis en Gel de Agar , Megasphaera/enzimología , Megasphaera/aislamiento & purificación , Especificidad por Sustrato , Veillonellaceae/enzimología , Veillonellaceae/aislamiento & purificaciónRESUMEN
The medium chain acyl-CoA dehydrogenase catalyzes the flavin-dependent oxidation of a variety of acyl-CoA thioesters with the transfer of reducing equivalents to electron-transferring flavoprotein. The binding of normal substrates profoundly suppresses the reactivity of the reduced enzyme toward molecular oxygen, whereas the oxidase reaction becomes significant using thioesters such as indolepropionyl-CoA (IP-CoA) and 4-(dimethylamino)-3-phenylpropionyl-CoA (DP-CoA). Steady-state and stopped-flow studies with IP-CoA led to a kinetic model of the oxidase reaction in which only the free reduced enzyme reacts with oxygen (Johnson, J. K., Kumar, N. R., and Srivastava, D. K. (1994) Biochemistry 33, 4738-4744). We have tested their proposal with IP-CoA and DP-CoA. The dependence of the oxidase reaction on oxygen concentration is biphasic with a major low affinity phase incompatible with a model predicting a simple Km for oxygen of 3 microM. If only free reduced enzyme reacts with oxygen, increasing IP-CoA would show strong substrate inhibition because it binds tightly to the reduced enzyme. Experimentally, IP-CoA shows simple saturation kinetics. The Glu376-Gln mutant of the medium chain dehydrogenase allows the oxygen reactivity of complexes of the reduced enzyme with IP-CoA and the corresponding product indoleacryloyl-CoA (IA-CoA) to be characterized without the subsequent redox equilibration that complicates analysis of the oxidase kinetics of the native enzyme. In sum, these data suggest that when bulky, nonphysiological substrates are employed, multiple reduced enzyme species react with molecular oxygen. The relatively high oxidase activity of the short chain acyl-CoA dehydrogenase from the obligate anaerobe Megasphaera elsdenii was studied by rapid reaction kinetics of wild-type and the Glu367-Gln mutant using butyryl-, crotonyl-, and 2-aza-butyryl-CoA thioesters. In marked contrast to those of the mammalian dehydrogenase, complexes of the reduced bacterial enzyme with these ligands react with molecular oxygen at rates similar to those of the free protein. Evolutionary and mechanistic aspects of the suppression of oxygen reactivity in the acyl-CoA dehydrogenases are discussed.
Asunto(s)
Acil-CoA Deshidrogenasas/metabolismo , Oxidorreductasas/metabolismo , Acil-CoA Deshidrogenasa , Acil-CoA Deshidrogenasas/genética , Animales , Simulación por Computador , Humanos , Riñón/enzimología , Modelos Químicos , Oxidación-Reducción , Oxígeno/metabolismo , Proteínas Recombinantes/metabolismo , Porcinos , Veillonellaceae/enzimología , Veillonellaceae/genéticaRESUMEN
Batch culture experiments showed that permeabilized cells and membranes of Ruminococcus albus and Fibrobacter succinogenes, acid-intolerant celluloytic bacteria, have only one-fourth to one-fifth as much H(+)-ATPase as Megasphaera elsdenii and Streptococcus bovis, which are relatively acid tolerant. Even in the cells grown in continuous culture at pH 7.0, the acid-intolerant bacteria contained less than half as much H(+)-ATPase as the acid-tolerant bacteria. The amounts of H(+)-ATPase in the acid-tolerant bacteria were increased by more than twofold when the cells were grown at the lowest pH permitting growth, whereas little increase was observed in the case of the acid-intolerant bacteria. These results indicate that the acid-intolerant bacteria not only contain smaller amounts of H(+)-ATPase at neutral pH but also have a lower capacity to enhance the level of H(+)-ATPase in response to low pH than the acid-tolerant bacteria. In addition, the H(+)-ATPases of the acid-intolerant bacteria were more sensitive to low pH than those of the acid-tolerant bacteria, although the optimal pHs were similar.
Asunto(s)
Bacterias/enzimología , ATPasas de Translocación de Protón/metabolismo , Rumen/microbiología , Animales , Bacterias Anaerobias/enzimología , Celulosa/metabolismo , Bacterias Anaerobias Gramnegativas/enzimología , Cocos Grampositivos/enzimología , Concentración de Iones de Hidrógeno , Streptococcus bovis/enzimología , Veillonellaceae/enzimologíaRESUMEN
The Fe-hydrogenase from Megasphaera elsdenii undergoes direct electron exchange with glassy carbon electrodes. Cyclic voltammetry defines the catalytic-performance of the enzyme over a continuous but precisely defined range of potentials. In the presence of H2 and protons the bias of the enzyme towards H2 production is readily visualised. Variation of the response with pH indicates that protein ionisations with pK of approximately 6.7 and 8.3 regulate the catalytic activity. Possible origins for these observations in the chemistry of the H2-activating site are discussed. The mid-wave potential of the catalytic response, Emid, is defined as the catalytic operating potential of the enzyme. Under an atmosphere of hydrogen Emid = -421 +/- 10 mV, pH 7 with a variation of -21 +/- 4 mV pH-1, 22 degrees C. Deviation of Emid from the thermodynamic potential of the hydrogen/proton couple reflects the enzyme's influence over the catalysed reaction. Emid is the reduction potential of the H2-activating centre (H-cluster) in the absence of kinetic bottle-necks at other steps in the reaction mechanism.
Asunto(s)
Hidrogenasas/química , Proteínas Hierro-Azufre/química , Veillonellaceae/enzimología , Aire , Monóxido de Carbono , Electroquímica , Concentración de Iones de Hidrógeno , Hidrogenasas/metabolismo , Proteínas Hierro-Azufre/metabolismoRESUMEN
Physiological concentrations [< 11 mM] of formate do not violate the metabolism of S. bovis and M. elsdenii. A significant inhibition is caused by concentrations of 22 and 44 mM. In this case the process of ammonia formation in S. bovis is inhibited more pronouncedly. Peculiar effects of formate (11 mM) on LDH, FDH, aconitase, isocitrate dehydrogenase, fumarase, L-MDH and malic-enzyme have been stated. The changes show that it enhances assimilation of sugars fermented to lactate in S. bovis, in contrast to M. elsdenii, where it activates the utilization of lactic acid. During the log-phase S. bovis utilized only 11.5% of [14C] H2O2, whereas M. elsdenii uses 33.4% of it. The major amount of the label is transferred from intracellular inclusions to nucleic acids (in S. bovis--74.7%, in M. elsdenii--87%) and then incorporated into low molecular substances (23.5 and 11.9%, respectively), the rest being incorporated into proteins and lipids.
Asunto(s)
Formiatos/metabolismo , Lactatos/biosíntesis , Lactatos/metabolismo , Rumen/microbiología , Streptococcus bovis/metabolismo , Veillonellaceae/metabolismo , Animales , Streptococcus bovis/enzimología , Veillonellaceae/enzimologíaRESUMEN
(R)-2-Hydroxyglutaryl-CoA dehydratase (HGDA/B) from Acidaminococcus fermentans requires an activator protein for activity. This activator (HGDC) has not yet been purified from its natural source due to its low concentration combined with an extreme sensitivity towards oxygen. Gene expression in Escherichia coli identified an open reading frame (780 bp) as the gene encoding HGDC. Dehydratase activity was stimulated at least tenfold by cell-free extracts of E. coli cells transformed with a plasmid carrying hgdC. On the chromosome the hgdC gene is located just before hgdA and hgdB.
Asunto(s)
Proteínas Bacterianas/metabolismo , Hidroliasas/metabolismo , Veillonellaceae/metabolismo , Secuencia de Aminoácidos , Proteínas Bacterianas/genética , Secuencia de Bases , Clonación Molecular , Activación Enzimática/genética , Escherichia coli , Genes Bacterianos , Datos de Secuencia Molecular , Oligodesoxirribonucleótidos , Sistemas de Lectura Abierta , Veillonellaceae/enzimología , Veillonellaceae/genéticaRESUMEN
Butyryl-CoA, crotonyl-CoA or 3-hydroxybutyryl-CoA all ultimately form an enzyme-acetoacetyl-CoA complex upon aerobic addition to butyryl-CoA dehydrogenase purified from Megasphaera elsdenii, implying the presence of crotonase activity. This behaviour remains even after treatment with 6M urea, which destroys the activity of the main crotonase fraction from M. elsdenii. Flavin-sensitised photoinactivation destroys residual crotonase and dehydrogenase activities in parallel. Butyryl-CoA dehydrogenase thus has intrinsic crotonase activity with a turnover rate (0.05 min-1) about 0.02% of the figure for dehydrogenase activity. Mechanistic implications are discussed.
Asunto(s)
Enoil-CoA Hidratasa/metabolismo , Ácido Graso Desaturasas/metabolismo , Veillonellaceae/enzimología , Acilcoenzima A/metabolismo , Butiril-CoA Deshidrogenasa , Ácido Graso Desaturasas/aislamiento & purificación , Luz , Urea/farmacologíaRESUMEN
1. The primary sodium-ion pump glutaconyl-CoA decarboxylase (GCD) from Acidaminococcus fermentans is composed of four subunits: GCDA, the carboxytransferase (65 kDa), GCDB, the carboxylyase (36 kDa), GCDC, the biotin carrier (24 kDa) and GCDD (14 kDa) of unknown function. A genomic library of A. fermentans was screened with an antiserum raised against whole GCD. A clone giving the strongest reaction in an immunoassay contained a 12-kbp genomic fragment from A. fermentans and was analysed further. An oligonucleotide deduced from the N-terminus of GCDA was used for probing the corresponding gene gcdA. It is 1761 bp in length and encodes for a protein of 64.3 kDa. Both partial amino acid sequences obtained from GCDA, the N-terminus as well as an internal tryptic peptide, were detected in the open reading frame (ORF) of gcdA. 2. Sequencing of the flanking regions revealed three adjacent ORF (ORF1-3) which do not code for any of the peptide sequences known of the other GCD subunits. The ORF downstream of gcdA (ORF3) is followed by hgdA and hgdB coding for 2-hydroxyglutaryl-CoA dehydratase, the preceding enzyme of the pathway of glutamate fermentation. Our results suggest that at least these three genes of the hydroxyglutarate pathway are organised in an operon and that the genes of the other GCD subunits from which peptide sequences are known (GCDB and GCDC) are not located adjacent to gcdA. 3. gcdA was amplified from genomic DNA using the polymerase chain reaction and cloned into the expression vector pJF118HE. Active GCDA subunit (up to 2.8 nkat/mg protein), catalysing the biotin-dependent formation of crotonyl-CoA from glutaconyl-CoA, was obtained in cell-free extracts of Escherichia coli DH5 alpha by moderately inducing the tac promoter of pJF118HE with 25-100 microM isopropyl-1-thio-beta-D-galactoside. Strong induction (1 mM isopropyl-1-thio-beta-D-galactoside) led to the formation of inclusion bodies from which GCDA could not be reactivated. The apparent Km = 51 mM for free biotin of the expressed GCDA subunit with V = 1.9 nkat/mg protein is similar to that of butanol-treated GCD composed of GCDA and GCDC (apparent Km = 40 mM). Biocytin was found to be a somewhat better carboxy acceptor for the expressed GCDA subunit (apparent Km = 13 mM; V = 1.0 nkat/mg protein). 4. Native GCD and expressed GCDA were treated with 2 mM N-ethylmaleimide showing different kinetics of inactivation: GCD lost half of its activity within 6 min, whereas expressed GCDA required 21 min.
Asunto(s)
Carboxiliasas/genética , Clonación Molecular , Escherichia coli/genética , Expresión Génica , Veillonellaceae/genética , Secuencia de Aminoácidos , Secuencia de Bases , Biotina/farmacología , Etilmaleimida/farmacología , Datos de Secuencia Molecular , Sondas de Oligonucleótidos , Sistemas de Lectura Abierta , Reacción en Cadena de la Polimerasa , Proteínas Recombinantes/metabolismo , Análisis de Secuencia de ADN , ATPasa Intercambiadora de Sodio-Potasio/genética , Transformación Bacteriana , Veillonellaceae/enzimologíaRESUMEN
Activity of D-lactate dehydrogenase (D-LDH) was shown not only in cell extracts from Megasphaera elsdenii grown on DL-lactate, but also in cell extracts from glucose-grown cells, although glucose-grown cells contained approximately half as much D-LDH as DL-lactate-grown cells. This indicates that the D-LDH of M. elsdenii is a constitutive enzyme. However, lactate racemase (LR) activity was present in DL-lactate-grown cells, but was not detected in glucose-grown cells, suggesting that LR is induced by lactate. Acetate, propionate, and butyrate were produced similarly from both D- and L-lactate, indicating that LR can be induced by both D- and L-lactate. These results suggest that the primary reason for the inability of M. elsdenii to produce propionate from glucose is that cells fermenting glucose do not synthesize LR, which is induced by lactate.
Asunto(s)
Glucosa/metabolismo , L-Lactato Deshidrogenasa/análisis , Lactatos/metabolismo , Racemasas y Epimerasas/análisis , Veillonellaceae/enzimología , Veillonellaceae/crecimiento & desarrollo , Acetatos/metabolismo , Acrilatos/metabolismo , Animales , Cromatografía DEAE-Celulosa , Medios de Cultivo , Activación Enzimática/efectos de los fármacos , Ácidos Grasos Volátiles/biosíntesis , Glucosa/farmacología , L-Lactato Deshidrogenasa/química , L-Lactato Deshidrogenasa/aislamiento & purificación , Lactatos/farmacología , Racemasas y Epimerasas/aislamiento & purificación , Relación Estructura-Actividad , Veillonellaceae/efectos de los fármacosRESUMEN
The hydrogenase of Megasphaera elsdenii was purified to a specific activity of 350 units/mg. The hydrogen-tritium exchange assay of Hallahan et al. [Hallahan, D.L., Fernandez, V. M., Hatchikian, E. C. and Hall, D. O. (1986) Biochimie (Paris) 68, 49-54] was adapted to allow its use in the study of the M. elsdenii hydrogenase preparation. Under the assay conditions routinely employed, the enzyme's exchange activity was inhibited by Tris/HCl and MgCl2; it was stimulated by ethylene glycol. Maximal activity in this standard assay occurred at pH 7.1. The effect of the concentration of molecular hydrogen (1H2 plus 3H1H) on the exchange activity was studied. The resulting double-reciprocal plot was linear; its slope and its intercepts on the ordinate and abscissa were pH-dependent. The rate equations for a number of models of the exchange activity were derived. Each model gave rise to a linear double-reciprocal plot at constant pH, but none could explain fully the observed effects of varying pH. The experimental data corresponded most closely to the predictions of models in which protons were treated both as substrates and as regulators of the enzyme's activity.
Asunto(s)
Hidrógeno/metabolismo , Hidrogenasas/metabolismo , Tritio/metabolismo , Veillonellaceae/enzimología , Tampones (Química) , Catálisis , Glicol de Etileno , Glicoles de Etileno/farmacología , Concentración de Iones de Hidrógeno , Hidrogenasas/antagonistas & inhibidores , Isótopos , Cinética , Oxígeno/metabolismoRESUMEN
Until now, workers in the field of fatty acid metabolism have suggested that the substrates are isopotential with the enzymes and that the reactions are forced to completion by the formation of charge-transfer complexes [Gustafson, W. G., Feinberg, B. A., & McFarland, J. T. (1986) J. Biol. Chem. 261, 7733-7741]. To date, no experimental evidence for this hypothesis exists. The work presented here shows that the butyryl-CoA/crotonyl-CoA couple is not isopotential with the enzymes with which it interacts. The potential of the butyryl-CoA/crotonyl-CoA couple (E ' = -0.013 V) is significantly more positive than the potential of either of the enzymes with which it interacts, bacterial butyryl-CoA dehydrogenase (E ' = -0.079 V) and mammalian general acyl-CoA dehydrogenase (E ' = 0.133 V). These data imply that the regulation of enzyme potential is essential for any electron transfer from substrate to enzyme to occur in mammalian or bacterial systems. In support of this assertion, a significant shift in potential for bacterial butyryl-CoA dehydrogenase (an analogue of the mammalian enzyme) in the presence of butyryl-CoA and crotonyl-CoA is reported. The potential is shifted positive by 60 mV. Larger potential shifts will undoubtedly be observed with the mammalian enzyme, which would be consistent with the catalytic direction of electron transfer.