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1.
Inhibition of the tempe mould, Rhizopus oligosporus, by ammonia 总被引:1,自引:0,他引:1
The hyphal extension rate of Rhizopus oligosporus NRRL 2710 was slowed in the presence of 0·42 and 0·84 mmol NH3 l−1 and inhibited by 1·3 mmol l−1 . Sporulation was prevented at NH3 concentrations of 0·42 mmol l−1 andabove. There was no evidence of toxicity due to NH+ 4 at concentrations up to 300 mmol l−1 .Independent of the concentrations of NH3 or NH+ 4 , the lower the pH value, in therange 6·0–9·0, the higher was the rate of hyphal extension. It is suggested that accumulationof toxic levels of NH3 could be responsible for the cessation of mould growth in tempe. 相似文献
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3.
R. C. Minussi M. C. Baracat-Pereira J. L. C. Coelho & D. O. Silva 《Letters in applied microbiology》1997,24(5):369-372
Pectin lyase (PL) from Penicillium griseoroseum can be induced by xanthine, theobromine, theophylline and especially by caffeine and hypoxanthine (5 mmol l−1 with 0·01% yeast extract (YE)). For caffeine and hypoxanthine, PL activity was, respectively, 5·2 and 3·7 times higher than with YE alone. The simultaneous addition of caffeine or hypoxanthine (5 mmol l−1 ) and YE (0·1%) had a synergistic effect on PL activity as compared to the addition of these substances alone (0·2% YE; 10 mmol l−1 caffeine; 10 mmol l−1 hypoxanthine). Increasing caffeine concentrations (0–10 mmol l−1 ) for a constant YE content of 0·01%, resulted in an increase in PL activity and a decrease in mycelial mass. For a constant caffeine concentration (5 mmol l−1 ) and increasing YE contents (0–0·2%), a higher PL activity and mycelial mass were detected. The addition of caffeine (10 mmol l−1 ) at the beginning of incubation increased PL activity and decreased mycelial mass, while caffeine added after 12 and 24 h resulted in decreases in PL activity and increases in mycelial mass. The results presented here indicate that methylxanthines, especially caffeine, can induce PL in P. griseoroseum . 相似文献
4.
Carvacrol, a natural plant constituent occurring in oregano and thyme, was investigated for its bactericidal effect towards the food-borne pathogen Bacillus cereus . Carvacrol showed a dose-related growth inhibition of B. cereus . At concentrations of 0·75 mmol l−1 and above, total inhibition of the growth was observed. Below this concentration, carvacrol extended the lag-phase, reduced the specific growth rate and reduced the maximum population density. Incubation for 40 min in the presence of 0·75–3 mmol l−1 carvacrol decreased the number of viable cells of B. cereus exponentially. Spores were found to be approximately 2·3-fold less sensitive to carvacrol than vegetative cells. Bacillus cereus cells showed reduced susceptibility towards carvacrol at pH 7·0 compared with different values between pH 4·5 and 8·5. The culture and exposure temperatures had a significant influence on the survival of vegetative cells. The highest death rate of cells was observed at an exposure temperature of 30 °C. Membrane fluidity was found to be an important factor influencing the bactericidal activity of carvacrol. 相似文献
5.
Abstract— A method is described for quantifying the GABA distribution in cat spinal cord at 200–500 μn resolution. Isolated spinal cord (L5–S1) was frozen and sectioned at about 150 μm thickness. The frozen tissue section was cut into 200 or 500 μm square blocks. The GABA content of each square tissue block was determined by enzymic micromethods and GABA distribution was mapped quantitatively. Average GABA concentrations were: 0·4 mmol/l. in white matter, 1·2 mmol/l. in ventral horn and 1·7 mmol/l. in dorsal horn. The highest concentrations of GABA (2–3 mmol/l.) were found in the dorsolateral part of dorsal horn. In order to destroy the interneurons of dorsal horn, the blood vessels supplying the dorsal horn of the lumbar enlargement were unilaterally cauterized. Seven to 30 days after operation, both the size of dorsal root potential and the GABA level in the dorsal horn were markedly reduced on the cauterized side. These results suggest that GABA is highly concentrated in the interneurons of dorsal horn and functions as a transmitter of presynaptic inhibition. 相似文献
6.
The effects of α-difluoromethylornithine (DFMO) on in vitro ornithine decarboxylase (ODC) activities from three plant pathogenic fungi, Pyrenophora avenae, Pyricularia oryzae and Uromyces viciae-fabae , were studied. DFMO concentrations from 0·01 to 1·0 mmol/l produced no significant effects on ODC activities from the three fungi. However, increasing the DFMO concentration to 5 mmol/l produced a substantial reduction in in vitro ODC activity from Pyre, avenae. The ODC inhibitor, α-monofluoromethylornithine (2 mmol/l), significantly reduced in vitro ODC activity from Pyre. avenae , whereas RR-methyl acetylenic putrescine, an ODC inhibitor based on putrescine, produced no significant effect on the fungal enzyme. 相似文献
7.
Biodegradation of softwood ( Pinus radiata ) by the ascomycete Chrysonilia sitophila was dependent on the nitrogen and glucose concentrations in the culture medium. Optimization studies of the delignification process, in which the nitrogen (0–50mmol/l NH+ 4 ) and glucose (0–2%) concentrations were varied, showed a maximal value of 17·8% for sawdust degradation in cultures containing 10 mmol/l NH4 + and 1·0% glucose. Solubility of the decayed sawdust in 1% NaOH at maximal delignification conditions showed a threefold increase and changes in the thermogravimetric pattern were also observed. Biodegraded wood chips showed significant decreases of the 280 and 310 nm characteristic lignin bands in the u.v. reflectance spectra. 相似文献
8.
Bifidobacterium adolescentis Int-57 isolated from human faeces produced extracellular amylase. The enzyme was purified from the culture supernatant fluids by ammonium sulphate precipitation, gel-filtration chromatography (Sephadex-G-75), ion-exchange chromatography (CM-cellulose) and FPLC. SDS-PAGE of the purified enzyme revealed a major band with an apparent molecular weight of 66 kDa. The pI was 5·2. Enzyme activity was optimal at 50°C, and at pH 5·5. The enzyme was stable at 20–40°C, and at pH 5–6 with a K m value of 2·4 g l−1 soluble starch. The activation energy was 42·3 kJ mol−1 . The enzyme was significantly inhibited by maltose (10%), glucose (10%), Cu2 + (5 mmol l−1 ), Zn2 + (5 mmol l−1 ), N- bromosuccinimide (5 mmol l−1 ), EDTA (5 mmol l−1 ), I2 (1 mmol l−1 ) and activated by β-mercaptoethanol (10 mmol l−1 ). 相似文献
9.
The genus Pectinatus has been often reported in beer spoilage with off-flavours. The bacteria are strictly anaerobic, Gram-negative rods. Propionate and acetate are the main fermentation products from glucose in the two species belonging to the genus, P. cerevisiiphilus and P. frisingensis. Amino acids routinely present at a high level in beer were not growth substrates for both species, and a significant accumulation of succinate was observed with lactate as growth substrate. Both Pectinatus ssp. showed almost identical fermentation balances on glucose. Growth kinetics of both glucose-grown species were unchanged under a N2 , H2 or 20% CO2 -containing atmosphere. Combinations of culture medium pH values from pH 3·9 to pH 7·2, of glucose levels between 5 and 55 mmol l-1 , and of lactate concentrations varied from 4 to 40 mmol l-1 demonstrated that biomass and volatile fatty acids production were proportional to glucose concentration for both Pectinatus species. A significant increase of volatile fatty acid production was measured for both species at the lowest pH values with a lactate or a glucose concentration increase. The maximum biomass production was observed at pH 6·2 for P. cerevisiiphilus , and between pH 4·5 and pH 4·9 for P. frisingensis. Glucose and lactate or pH value were dependent with regard to propionate and acetate production in P. frisingensis. On the other hand, the variations of these three parameters were independent with regard to biomass production for both strains, and to volatile fatty acids production for P. cerevisiiphilus. Addition of ethanol to glucose-grown cultures completely inhibited growth at 1·3 mol l-1 ethanol for P. cerevisiiphilus , and at 1·8 mol l-1 for P. frisingensis. 相似文献
10.
The bacterium Arthrobacter ilicis isolated from the marine sponge Spirastrella sp. produces extracellular serine type acetylcholinesterase. The maximum enzyme activity was found at 45 °C and pH 8·0. The activation and deactivation energies, calculated from an Arrhenius plot, were 13·68 and 36·96 kcal mol−1 , respectively. The enzyme was not affected by the addition of the major cations of sea water, such as Ca2+ and Mg2+ at 25 mmol l−1 , and was strongly inhibited by EDTA and different organophosphorus and carbamate compounds at 5 mmol l−1. 相似文献
11.
Of various commercial enzyme preparations examined, Cytolase M102 was found to contain the highest glucosyltransferase activity (55 U ml−1 ). It rapidly converted maltose to panose (Glcα1 → 6Glcα1 → 4Glc) with a V max value of 5·8 mmol l−1 min−1 at 50°C in 0·05 mol l−1 sodium acetate buffer (pH 4·4). The K m value of the enzyme for maltose was 750 mmol l−1 . Yields of panose and glucose after 45 min of reaction, for example, were 47·2% and 52·8%, respectively, on the basis of the amount of maltose consumed. 相似文献
12.
An extracellular phenolic acid esterase produced by the fungus Penicillium expansum in solid state culture released ferulic and ρ-coumaric acid from methyl esters of theacids, and from the phenolic-carbohydrate esters O-[5-O-(trans-feruloyl)-α- l -arabinofuranosyl]-(1 → 3)-O-β- d -xylopyranosyl-(1 → 4)- d -xylopyranose (FAXX) and O-[5-O-((E)-ρ-coumaroyl)-α- l -arabinofuranosyl]-(1 → 3)-O-β- d -xylopyranosyl-(1 → 4)- d -xylopyranose (PAXX). The esterase was purified 360-fold in successive stepsinvolving ultrafiltration and column chromatography by gel filtration, anion exchange andhydrophobic interaction. These chromatographic methods separated the phenolic acid esterasefrom α- l -arabinofuranosidase, pectate and pectin lyase, polygalacturonase,xylanase and β- d -xylosidase activities. The phenolic acid esterase had an apparentmass of 65 kDa under non-denaturing conditions and a mass of 57·5 kDa underdenaturing conditions. Optimal pH and temperature were 5·6 and 37 °C,respectively and the metal ions Cu2 + and Fe3 + atconcentrations of 5 mmol l−1 inhibited feruloyl esterase activity by 95% and44%, respectively, at the optimum pH and temperature. The apparent Km and Vmax of the purified feruloyl esterase for methyl ferulate at pH 5·6 and 37 °Cwere 2·6 mmol l−1 and 27·1 μmol min−1 mg−1 . The corresponding constants of ρ-coumaroylesterase for methyl coumarate were 2·9 mmol l−1 and 18·6 μmol min−1 mg−1 . 相似文献
13.
The sub-chronic (28–56 days) effects of exposure to low concentrations of cadmium (Cd; 0·05, 0·25, 0·50 and 2·50 μg l−1 ) shortly following fertilization on embryos, larvae and juvenile rainbow trout Oncorhynchus mykiss were examined. Premature hatching occurred at lower concentrations (0·05 and 0·25 μg l−1 Cd), however, delayed hatching was seen in the 2·50 μg l−1 Cd group, with >90% of hatching occurring on the last day of the hatching period. Larval growth was negatively affected by Cd exposure in a concentration-dependent manner. Larvae exposed to 2·50 μg l−1 Cd were 13·9 ± 0·8% shorter in total length ( L T ) and weighed 22·4 ± 3·5% (mean ± s . e .) less than controls at the end of the exposure period. Plasma sex steroid concentrations (oestradiol in juvenile females and 11-ketotestosterone in juvenile males) were elevated (four- to 10-fold over controls) in exposed fish in both males and females, following 28 days of exposure to 0·05, 0·25 and 0·50 μg l−1 Cd, respectively. These results suggest that environmentally realistic concentrations (in the μg l−1 range) of Cd can affect the development of O. mykiss impacting embryos, larvae and juvenile fish. 相似文献
14.
In strictly anaerobic conditions in a culture medium adjusted to pH 5·2 with HCl and incubated at 30°C, inocula containing < 10 vegetative bacteria of Clostridium botulinum ZK3 (type A) multiplied to give > 108 bacteria per ml in 3 d. Growth from an inoculum of between 10 and 100 spores occurred after a delay of 10–20 weeks. Citric acid concentrations of 10–50 mmol/l at pH 5·2 inhibited growth from both vegetative bacteria and spore inocula, a concentration of 50 mmol/l increasing the number of vegetative bacteria or of spores required to produce growth by a factor of approximately 106 . The citric acid also reduced the concentration of free Ca2+ in the medium. The inhibitory effect of citric acid on vegetative bacteria at pH 5·2 could be prevented by the addition of Ca2+ or Mg2+ and greatly reduced by Fe2+ and Mn2+ . The addition of Ca2+ , but not of the remaining divalent metal ions, restored the concentration of free Ca2+ in the medium to that in the citrate-free medium. The inhibitory effect of citric acid on growth from a spore inoculum was only partially prevented by Ca2+ . Citric acid (50 mmol/l) did not inhibit growth of strain ZK3 at pH 6 despite the greater chelating activity of citrate at pH 6 than at pH 5·2. The effect of citric acid and Ca2+ at pH 5·2 on vegetative bacteria of strains VL1 (type A) and 2346 and B6 (proteolytic type B) was similar to that on strain ZK3. 相似文献
15.
High- and Low-Affinity Transport of D-Glucose from Blood to Brain 总被引:21,自引:19,他引:2
Albert Gjedde 《Journal of neurochemistry》1981,36(4):1463-1471
Abstract: Measurements of the unidirectional blood-brain glucose flux in rat were incompatible with a single set of kinetic constants for transendothelial transport. At least two transfer mechanisms were present: a high-affinity, low-capacity system, and a low-affinity, high-capacity system. The low-affinity system did not represent passive diffusion because it distinguished between D-and L-glucose. The Tmax and K m , for the high-affinity system were 0.16 mmol 100 g−1 min−1 and 1 mM; for the low-affinity system, ∼ 5 mmol 100 g−1 min−1 and ∼ 1 M. With these values, physiological glucose concentrations were not sufficient to saturate the low-affinity system. In normoglycemia, therefore, three independent pathways of glucose transport from blood to brain appear to exist: a high-affinity facilitated diffusion pathway of apparent permeability 235·10−7 cm s−1 , a specific but nonsaturable diffusion pathway of permeability 85·10−7 cm s−l , and a nonspecifc passive diffusion pathway of permeability 2·10−7 cm s−1 . 相似文献
16.
H. Y. Ogata 《Journal of fish biology》2002,61(6):1504-1512
Juvenile yellowtail Seriola quinqueradiata (initial body mass of 22 g) were fed either a commercial diet (control, diet 1) or diets supplemented with histidine (diet 2), histidine+β-alanine (diet 3), or histidine+β-alanine+thyroxine (diet 4), for 6 weeks. The dietary treatment did not affect the final body mass. Free histidine levels of white muscle in the fish fed the diets supplemented with histidine (diets 2-4) were significantly higher (>62 mmol kg−1 of wet tissue) than that of control group (42 mmol kg−1 of wet tissue). Dietary supplementation of β-alanine (diet 3) or β-alanine+thyroxine (diet 4) failed to increase muscle anserine (β-alanyl-π-L.-histidine) level. Muscle buffering capacity of the range from pH 6·0 to 7·5 of the fish fed the diets 2-4 (41·6-42·7 mmol NaOH pH−1 kg muscle−1 ) reflected the increase of muscle histidine level, having slightly but significantly intensified compared to control fish (36·6 mmol NaOH pH−1 kg muscle−1 ). Most of the free amino acids other than histidine were significantly lower in the fish fed the diets 2-4 than in control fish. Thus, crystalline histidine supplemented to diets appears to be deposited in muscular tissue, and consequently enhance muscle buffering capacity in this species. 相似文献
17.
Solubility of zinc and interactions between zinc and phosphorus in the hyperaccumulator Thlaspi caerulescens 总被引:5,自引:0,他引:5
The relationship between Zn and P in the Zn hyperaccumulator Thlaspi caerulescens J. & C. Presl was investigated using hydroponic culture. Total concentrations of Zn in the shoots increased from 0·2 to 27 g kg–1 dry mass when solution Zn increased from 1 to 1000 mmol m–3 . Water-soluble Zn accounted for > 80% of the total Zn in the shoots containing > 5 g Zn kg–1 dry mass. Total P was maintained at about 3 g kg–1 dry mass in the shoots containing < 20 g Zn kg–1 dry mass, but significantly decreased with higher Zn concentrations. Linear regression between insoluble P and insoluble Zn in the shoots produced a small slope, suggesting that co-precipitation of Zn and P was not an important detoxification mechanism in the shoots. In contrast, there was a strong correlation between insoluble P and insoluble Zn in the roots, with a linear slope of 0·3 — close to the P:Zn ratio in Zn3 (PO4 )2 . Foliar sprays of phosphate did not affect shoot dry mass significantly, but decreased root length and root dry mass significantly at Zn concentrations in solution from 10 to 3000 mmol m–3 . Foliar P was translocated to roots to enhance co-precipitation of Zn and P, although this did not enhance Zn tolerance. The results suggest that T.caerulescens possesses mechanisms which allow it to accumulate and sequester huge amounts of Zn in the shoots without causing P deficiency. 相似文献
18.
Aims: To investigate the effects of salicylates in Saccharomyces cerevisiae exposed to oxidative stress induced by hydrogen peroxide (H2 O2 ).
Methods and Results: Saccharomyces cerevisiae was cultured through to the postlogarithmic phase of growth. Stress was induced by the addition of 1·5 mmol l−1 H2 O2 for 1 h, while N-acetyl-l-cysteine (NAC) and glutathione (GSSG) were used as control agents that affect the redox balance. Sodium salicylate, at 0·01–10 mmol l−1 or acetylsalicylic acid, at 0·02–2·5 mmol l−1 was administered at various times before hydrogen peroxide stress. Both agents conferred resistance to a subsequent hydrogen peroxide stress, similarly to the induction of the adaptive response observed upon pretreatment with NAC and GSSG. Sodium salicylate was more potent as a short-term, but not as a long-term pretreatment agent, compared to acetylsalicylic acid.
Conclusions: Pharmacological pretreatment with salicylates resulted in dose related increases in cell survival, indicating the induction of the protective response in yeast.
Significance and Impact of the study: The possible role of salicylates in the modulation of the hydrogen peroxide stress response in eukaryotic cells address questions on the effects of these commonly used therapeutic agents in a number of disorders exhibiting an oxidative stress component. 相似文献
Methods and Results: Saccharomyces cerevisiae was cultured through to the postlogarithmic phase of growth. Stress was induced by the addition of 1·5 mmol l
Conclusions: Pharmacological pretreatment with salicylates resulted in dose related increases in cell survival, indicating the induction of the protective response in yeast.
Significance and Impact of the study: The possible role of salicylates in the modulation of the hydrogen peroxide stress response in eukaryotic cells address questions on the effects of these commonly used therapeutic agents in a number of disorders exhibiting an oxidative stress component. 相似文献
19.
I. Castillo T. Requena P. Fernández de Palencia J. Fontecha M. Gobbetti 《Journal of applied microbiology》1999,86(4):653-659
An intracellular esterase from Lactobacillus casei subsp. casei IFPL731 was purified 1000-fold by ion exchange chromatography and gel filtration chromatography. The relative molecular mass of the native enzyme was 105 kDa, while the subunit molecular mass was estimated to be 38 kDa. The esterase hydrolysed tributyrin and had a preference for esters of short-chain fatty acids (butyrate, caproate and caprylate), while it did not hydrolyse palmitate and sterate esters. The apparent Michaelis-Menten constant of the enzyme on p -nitrophenyl butyrate was 0·3 mmol l−1 while on p -nitrophenyl caprylate, it was 0·04 mmol l−1 . The esterase was active over a broad range of pH and temperature values, and retained about 50% of maximal activity at pH 5·0 and 12 °C. Activity was strongly inhibited by 5 mmol l−1 phenylmethylsulphonyl fluoride, β-mercaptoethanol and N -ethylmaleimide, and was stimulated by Zn2+ at 1 mmol l−1 . 相似文献
20.
M. Petruccioli L. Brimer A. R. Cicalini F. Federici 《Journal of applied microbiology》1999,86(2):302-310
Mucor circinelloides LU M40 produced 12·2 mU ml−1 of linamarase activity when grown in a 3 l fermenter in the following optimized medium (g l−1 deionized water): pectin, 10·0; (NH4 )2 SO4 ,
1·0; KH2 PO4 , 2·0; Na2 HPO4 , 0·7; MgSO4 .7H2 O, 0·5; yeast extract, 1·0; Tween-80,
1·0, added after 48 h of fermentation. The purified linamarase was a dimeric protein with a molecular mass of 210 kDa; the enzyme showed optimum catalytic activity at pH 5·5 and 40 °C and had a wide range (3·0–7·0) of pH stability. The enzyme substrate specificity on plant cyanogenic glycosides was wide; the Km value for linamarin was 2·93 mmol l−1 . The addition, before processing, of the fungal crude enzyme to cassava roots facilitated and shortened detoxification; after 24 h of fermentation, all cyanogenic glycosides were hydrolysed. 相似文献
1·0; KH
1·0, added after 48 h of fermentation. The purified linamarase was a dimeric protein with a molecular mass of 210 kDa; the enzyme showed optimum catalytic activity at pH 5·5 and 40 °C and had a wide range (3·0–7·0) of pH stability. The enzyme substrate specificity on plant cyanogenic glycosides was wide; the K