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1.
Abstract Acetobacterium woodii was continuously grown on 3,4,5-trimethoxybenzoate as pure culture or in commensalistic combination with Pelobacter acidigallici and Desulfobacter postgatei . Under pure culture conditions the following growth parameters were determined: μ max= 0.112 h−1, K s= 1.07 mM, Y max= 35 g/mol, and m = 0.22 mmol·g−1·h−1. In coculture with P. acidigallici the affinity for the substrate increased and the K s value was found to be 135 μM. Under batch culture conditions mixed populations of A. woodii, P. acidigallici , and D. postgatei completely mineralized 3,4,5-trimethoxybenzoate to CO2, whereas under continuous culture conditions more than 3 mM acetate remained unused.  相似文献   

2.
Abstract The effect of cadmium (Cd) on methane formation from methanol and/or H2–CO2 by Methanosarcina barkeri was examined in a defined growth medium and in a simplified buffer system containing 50 mM Tes with or without 2 mM dithiothreitol (DTT). No inhibition of methanogenesis by high concentrations of cadmium was observed in growth medium. Similarly, little inhibition of methanogenesis by whole cells in the Tes buffer system was observed in the presence of 430 μM Cd or 370 μM mercury (Hg) with 2 mM DTT. When the concentration of DTT was reduced to 0.4 mM, almost complete inhibition of methanogenesis from H2–CO2 and methanol by 600 μM Cd was observed. In the absence of DTT, 150 μM Cd inhibited methanogenesis from H2–CO2 completely and from methanol by 97%. Methanogenesis from H2–CO2 was more sensitive to Cd than that from methanol.  相似文献   

3.
Metabolism of nitric oxide in soil and denitrifying bacteria   总被引:1,自引:0,他引:1  
Abstract Production and consumption of NO was measured under anaerobic conditions in a slightly alkaline and an acidic soil as well as in pure cultures of denitrifying Pseudomonas aeruginosa, P. stutzeri, P. fluorescens, Paracoccus denitrificans, Azospirillum brasilense , and A. lipoferum . Growing bacterial cultures reduced nitrate and intermediately accumulated nitrite, NO, N2O, but not NO2. Addition of formaldehyde inhibited NO production and NO consumption. In the presence of acetylene NO was reduced to N2O. Net NO release rates in denitrifying bacterial suspensions and in soil samples decreased hyperbolically with increasing NO up to mixing ratios of about 5 ppmv NO. This behaviour could be modelled by assuming a constant rate of NO production simultaneously with a NO consumption activity that increased with NO until V max was reached. The data allowed calculation of the gross rates ( P ) of NO production, of the rate constants ( k ), V max and K m of NO consumption, and of the NO compensation mixing ratio ( m c). In soil, P was larger than V max resulting in net NO release even at high NO mixing ratios unless P was selectively inhibited by chlorate + chlorite or by aerobic incubation conditions. In bacteria, V max was somewhat larger than P resulting in net NO uptake at high NO mixing ratios. Both P and V max were dependent on the supply of electron donor (e.g. glucose). Both in soil (aerobic or anaerobic) and in pure culture, the K m values of NO consumption were in a similar low range of about 0.5–6.0 nM. Anaerobic soil and denitrifying bacteria exhibited m c values of 1.6–2.1 ppmv NO and 0.2–4.0 ppmv NO, respectively.  相似文献   

4.
Abstract The uptake and incorporation of 75[Se]selenite by Butyrivibrio fibrisolvens and Bacteroides ruminicola were by constitutive systems. Rates of uptake were higher in chemostat culture than in batch culture and there may be some inducible component. Uptake of [75Se]selenite was distinct from sulphate or selenate transport, since sulphate and selenate did not inhibit selenite uptake, nor could sulphate or selenate uptake be demonstrated in these organisms. Selenite uptake in B. fibrisolvens had and apparent K m of 1.74 mM and a V max of 109 ng Se · min−1· (mg protein)−1. An apparent K m of 1.76 mM and V max of 1.5 μg Se · min−1· (mg protein)−1 was obtained for B. ruminicola . [75Se]Selenite uptake by both organisms was partially sensitive to inhibition by 2,4-DNP. Uptake by B. fibrisolvens was also partially inhibited by azide and arsenate and in B. ruminicola it was partially inhibited by fluoride. CCCP, CPZ, DCCD or quinine did not inhibit uptake in either B. fibrisolvens or B. ruminicola . Selenite transport by both organisms was sensitive to IAA and NEM and was strongly inhibited by sulphite and nitrite. [75Se]Selenite was converted to selenocystine, selenohomocystine and selenomethionine by B. fibrisolvens. B. ruminicola did not incorporate [75Se]selenite into organic compounds, but did reduce it to red elemental selenium.  相似文献   

5.
N 5 N 10-Methylenetetrahydromethanopterin reductase was purified 13-fold to apparent homogeneity from methanol grown Methanosarcina barkeri . The colourless enzyme was found to be composed of four identical subunits of apparent molecular mass 36 kDa. It catalysed the reduction of methylenetetrahydromethanopterin ( K m=15 μM) to methyltetrahydromethanopterin with reduced coenzyme F420 ( K m=12 μM) at a specific rate ( V max) of 2200 μmol min−1· mg protein−1 ( K cat=1320 s−1). With respect to coenzyme specificity, molecular properties and catalytic mechanism the enzyme was found to be similar to CH2=H4MPT reductase of Methanobacterium thermoautotrophicum which phylogenetically is only distantly related to M. barkeri .  相似文献   

6.
The Uptake of Carnitine by Slices of Rat Cerebral Cortex   总被引:5,自引:3,他引:2  
Abstract: The properties of carnitine transport were studied in rat brain slices. A rapid uptake system for carnitine was observed, with tissue-medium gradients of 38 ± 3 for L-[14CH3]carnitine and 27 ± 3 for D-[14CH3]carnitine after 180 min incubation at 37°C in 0.64 mM substrate. Uptake of L- and D-carnitine showed saturability. The estimated values of K m for L- and D-carnitine were 2.85 mM and 10.0 mM, respectively; but values of V max (1 μmol/min/ml in-tracellular fluid) were the same for the two isomers. The transport system showed stereospecificity for L-carnitine. Carnitine uptake was inhibited by structurally related compounds with a four-carbon backbone containing a terminal carboxyl group. L-Carnitine uptake was competitively inhibited by γ-butyrobetaine ( K i= 3.22 mM), acetylcarnitine ( K i= 6.36 mM), and γ-aminobutyric acid ( K i= 0.63 mM). The data suggest that carnitine and γ-aminobutyric acid interact at a common carrier site. Transport was not significantly reduced by choline or lysine. Carnitine uptake was inhibited by an N2 atmosphere, 2,4-dinitrophenol, carbonylcyanide- N -chlorophenylhydrazone, potassium cyanide, n-ethylmaleimide, and ouabain. Transport was abolished by low temperature (4°C) and absence of glucose from the medium. Carnitine uptake was Na+-dependent, but did not require K+ or Ca2+.  相似文献   

7.
Abstract A new transport system for the uptake of l-glutamate was characterized in Corynebacterium glutamicum strain Δ glu, in which the previously described binding protein-dependent glutamate uptake system is not present. Kinetic characterization revealed a highly specific secondary transport system, dependent on sodium ions. Glutamate uptake showed Michaelis-Menten kinetics, with a K m of 0.6 mM and a V max of 15 nmol min−1 (mg dw)−1. For the co-transported sodium ions, a relatively low K m of 3.3 mM was determined.  相似文献   

8.
Abstract— The kinetics of the uptake from blood to brain of pyruvate, lactate and glucose have been determined in rats of different ages. The carotid artery single injection technique was used in animals anaesthetized with pentobarbital. The rates of influx for each substrate were determined over a range of concentrations for the different age-groups. Data were analysed in terms of the Michaelis-Menten equation with a component to allow for non-saturable diffusion. Values are given for K m, V max and K d. In suckling rats (15-21 days) the V max values for both pyruvate and lactate were 2.0 μmol g−1 min−1. In 28-day-old rats the V max values had fallen to one-half and in adults they were less than one-tenth. K m, values were higher in the younger animals. The rate of glucose transport in suckling rats was half that of 28-day-old and adults although there was no difference with age in the K m values.
The results are discussed in relation to the net flux of these substrates in and out of brain during different stages of post-natal development.  相似文献   

9.
The presence of oxygen in rumen liquor and its effects on methanogenesis   总被引:4,自引:1,他引:3  
In situ measurement of O2 in the rumen liquor of cows, sheep and goats using a membrane-covered O2 electrode revealed the presence of up to 1630 nmol/l O2; O2 became undetectable immediately after feeding of animals. The effects of O2 on H2 production and methanogenesis in samples of rumen liquor were investigated using a mass spectrometer fitted with a membrane inlet system. Methanogenesis was totally and irreversibly inhibited after short term exposure (about 10 min) to 5 KPa (0·05 atm) O2; H2 production was unaffected. Glucose additions produced rapid transient increases in H2 levels and increased O2 uptake.  相似文献   

10.
Abstract The addition of 1 mM glycine betaine to the growth medium of Chromatium sp. NCIMB 8379 relieved growth inhibition caused by exposure to supra-optimal Nad concentrations. Intracellular glycine betaine concentrations were dependent upon the NaCl concentration of the growth medium up to 3 M exogenous Nad. Kinetic data for the accumulation of [methyl-14C]-glycine betaine demonstrated that Chromatium sp. NCIMB 8379 possesses a constitutively expressed active transport system for glycine betaine. The transport system was saturable with respect to glycine betaine concentration and exhibited typical Michaelis-Menten type kinetics: K m= 24 μ M, V max= 306 nmol min−1 mg protein−1 at an external NaCl concentration of 1 M. The rate of glycine betaine transport decreased progressively with increasing growth medium NaCl concentration. This transport system may represent an adaptive response to growth in high osmolarity environments in this halotolerant isolate, allowing accumulation of glycine betaine from the external cell environment or recycling synthesised glycine betaine which has passively diffused from the cell.  相似文献   

11.
Adaptation of Escherichia coli growth rates to the presence of pBR322   总被引:1,自引:0,他引:1  
Changes in the growth rate of Escherichia coli K12 J62-1 in response to the presence of plasmid pBR322 have been investigated. Plasmid-free and plasmid-containing strains were grown in batch culture and their maximum specific growth rate (μmax) determined. The acquisition of pBR322 by the host resulted in a decreased μmax. Following repeated subculturing of the plasmid-containing strain on selective medium, restoration in μmax was observed. The copy number and structure of the plasmid were not significantly altered during the experiment Growth rate measurements for a series of strains constructed using a combination of host cells and plas-mids with and without culture histories, indicated that the site of the adaptive mutation was located on the host chromosome rather than on the plasmid.  相似文献   

12.
Abstract: K m and V max values of monoamine oxidase (MAO) A and B towards 5-hydroxytryptamine were determined for rat brain homogenates after the in vitro inhibition of one of the two forms by the selective inhibitors clorgyline and l -deprenyl. K m values of 178 and 1170μ m , and V max values of 0.73 and 0.09 nmol·mg protein−1·min−1 towards 5-hydroxytryptamine were found for MAO-A and -B, respectively. The K 1 for 5-hydroxytryptamine as a competitive inhibitor of β-phenethylamine oxidation by MAO-B was found to be 1400 μm. The significance of these findings is discussed.  相似文献   

13.
Abstract— The unidirectional transport of metabolic substrates from blood to brain may be defined in terms of Michaelis-Menten saturable ( K m, V max) and non-saturable ( K d) components of influx. Various computation procedures have been previously reported to estimate the kinetic parameters when an intracarotid injection technique is used. Transformations of the influx data which allow linear plots to obtain estimates were compared with estimates obtained directly from a best fit on a least means squares criterion for both experimental and simulated data. Large discrepancies were apparent between the various estimates of the kinetic parameters when an equal weight was given to transformed data. For pyruvate (21-day-old rats), K m, values varied between 1.02 and 6.25 mM and V max varied between 0.68 and 2.30 μmol g−1 min−1. The estimates were almost equivalent when pyruvate data was re-analysed using a weighting scheme based on the finding that the absolute value of the S.D. of influx increased in proportion to influx. It is recommended that estimates of kinetic parameters be obtained by an iterative, non-linear least squares method to fit appropriately weighted data directly.  相似文献   

14.
Abstract Whole cells of the dinitrogen-fixing cyanobacterium Anabaena sp. PCC7120 exhibited K m values for l -glutamine and l -glutamate of 33 μM and 0.5 mM, respectively. V max of uptake was ca. 30 nmol mg−1 (chlorophyll) min−1 for both amino acids. The similar pattern of sensitivity to other amino acids exhibited by both transport activities suggests that a common transport system is involved in glutamine and glutamate uptake by this cyanobacterium.  相似文献   

15.
Abstract A cellulase gene from Ruminococcus flavefaciens FD-1 had previously been cloned in Escherichia coli . The product of this gene, CelA, was purified from E. coli and characterised. This 39 kDa cellulase is antigenically related, and of similar mass, to a protein in R. flavefaciens . The enzyme has cellodextrinase activity with predominantly exo-type action. CelA activity was optimal at pH 6.5 and 41°C, and was inhibited in the presence of divalent metal cations. The K m and V max were determined as 0.68 mM and 1.89 μmol min−1 mg−1 of CelA, respectively. Cellobiose was the major end product of cellodextrin hydrolysis, and our results suggest that celluboise is competitive inhibitor of CelA.  相似文献   

16.
A study of the β-galactosidase produced by the psychrotrophic bacterium Buttiauxella agrestis has been carried out. This micro-organism was isolated from raw milk and the enzyme isolated using standard methods. Molecular mass was estimated to be 515 kDa. The isoelectric point was close to 4·45. Optimum pH was 7·25. Maximal activity was observed at 50°C and activation energy was estimated to be 39·1 kJ mol-1. Lactose enhanced thermal stability. Using α-nitrophenyl-β-D-galactopyranoside as the substrate, the K m was 11 μmol 1-1 and V max was 85 U mg-1 protein. β-Mercaptoethanol and ethanol were inhibitors; glycerol acted as a complex effector. The enzyme required divalent cations for activity while it was inhibited by EDTA. When the enzyme was immobilized in diethyl aminoethylcellulose the optimum pH of activity was 8. K m was 47 μmol 1-1 and V max was 96 U mg-1 protein.  相似文献   

17.
The effects of different gaseous atmospheres were determined on the maximum specific growth rate (μmax) and end-product formation by Brochothrix thermosphacta ATCC 11509T, Lactobacillus viridescens SMRICC 174 and Lactobacillus sp. SMRICC 173 (homofermentative). The highest μmax-values for Lact. viridescens (0.47/h) and Broc. thermosphacta (0.49/h) were obtained in air. Under anaerobic conditions μmax was reduced, an atmosphere containing CO2 alone giving the greatest reduction. Lactobacillus sp. 173 did not grow in air or N2. Aerobic growth was obtained by adding peroxidase while anaerobic growth occurred in the presence of 5–20% CO2. Carbon dioxide alone reduced the growth rate. All test organisms produced mainly lactic acid anaerobically. Lactobacillus viridescens also produced ethanol while Broc. thermosphacta produced small amounts of ethanol and formic acid. With O2 present, the number of end-products increased for all organisms. Lactobacillus sp. 173 produced small amounts of acetic acid and acetoin together with lactic acid. Oxygen induced acetic acid production in Lact. viridescens and Broc. thermosphacta . Aerobically, Broc. thermosphacta also produced a large amount of acetoin and smaller amounts of 2,3-butanediol, iso -valeric acid and iso -butyric acid. The production of lactic acid by Broc. thermosphacta was completely prevented under strictly aerobic conditions. All test organisms consumed O2 during aerobic growth. Hydrogen peroxide was produced by Lact. viridescens and Lactobacillus sp. 173.  相似文献   

18.
Methanosarcina barkeri strain Fusaro was grown on a mixed substrate medium of methanol and acetate. When 50 mM of acetate was added to the methanol basal medium (250 mM), the rates of methane production, methanol consumption, cell growth and corrinoid production were stimulated 3.2, 2.7, 3.5, and 2.4 times, respectively compared with those in methanol alone. Addition of acetate also has significant influence on corrinoid distribution decreasing the intracellular corrinoid content from 6.8 to 3.0 mg/g dry cell and increasing the extracellular corrinoid concentration from 4.0 to 5.4 mg/l. The carbon balance analysis for methanogenesis and cellular growth with or without acetate addition revealed that about 50% of the utilized acetate carbon might be incorporated in the cellular materials and the remaining might be oxidized to generate the electrons which stimulate the methanol reduction to methane, accelerating the metabolic activities of the methanogenesis from methanol consequently enhancing the rates of methane and corrinoid production, and cell growth.  相似文献   

19.
Abstract: 1,4-μ-Glucan synthase activity, but not 1,3-μ-glucan-synthase activity, from Saprolegnia monoica was stimulated by cyclic-diguanylic acid, an immediate activator of Acetobacter xylinum - cellulose synthase. This activator, which increased the V max without modifying the K m for UDP-glucose, was active on solubilized and partially purified enzymes. These results suggest that the fungal system shares a common regulatory mechanism with the bacterial system.  相似文献   

20.
Abstract β-xylosidase (EC 3.2.1.37) has been purified from Aspergillus nidulans mycelium grown on oat-spelt xylan as sole carbon source. Its pH optimum for activity was found to be 5.0 and the optimum temperature was 50 °C. Its molecular mass was estimated by gel filtration to be 180000. Using p-nitrophenyl-β-d-xylopyranoside as substrate, the K m and V max values have been found to be 1.1 mM and 25.6 μmol min−1(mg protein)−1, respectively. Enzyme activity was inhibited by Hg2+, Ag2+, and Cu2+ at a concentration of 1 × 10−3 M. The synthesis of β-xylosidase in A. nidulans is strongly induced by arabinose and xylose and is subject to carbon catabolite repression mediated by the cre A gene product.  相似文献   

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