Production of β-glucosidase (cellobiase) by Curvularia sp.

A Curvularia sp. isolated from soil was found to produce extracellular β-glucosidase activity when grown in yeast extract, peptone, carboxymethylcellulose (YPC) medium. An initial medium pH of 6·5 and cultivation temperature of 30°C were found to be most suitable for high enzyme productivity. The pH and temperature optima for the enzyme were 4·0 and 70°C, respectively. Under these conditions, the enzyme exhibited a K_m (0-nitrophenyl-β- d -glucoside) value of 0.20 mmol/l. Several divalent metal ions inhibited enzyme activity at high concentration. EDTA. also inhibited β-glucosidase activity.     

Purification and characterization of β-amylase from leaves of potato (Solanum tuberosum)

Amylolytic activity is widely distributed in plants. In potato leaves ( Solanum tuberosum L.) the abundant amylolytic activity was found to be β-amylase (EC 3.2.1.2, a-1,4-D-glucan maltohydrolase). β-Amylase from potato leaves was purified to homogeneity for study of enzyme characteristics. The purification steps included ammonium sulphate precipitation, anion exchange chromatography, affinity chromatography and gel filtration. The end product of α-1,4-glucan degradation was maltose. The protein is a 111-kDa homo-dimer with a subunit molecular mass of 56 kDa and a pl of 5.6. The pH-optimum is 6.5 using p -nitrophenylmaltopentaoside (PNPG5) as substrate. The optimal temperature for hydrolysis is at 40°C. The enzyme is unstable at temperatures above 40°C. The K_nt-value for PNPG5 is 0.73 m M and the activity is inhibited by cyclodextrins. At a concentration of 1 m M , β-cyclodextrin is a stronger inhibitor than α-cyclodextrin (68 and 20% inhibition, respectively). Branched glucans (e.g. starch and amylopectin) are superior substrates as compared to long, essentially unbranched glucans (e.g. amylose). This study of the catalytic properties of β-amylase from potato leaves indicates the importance of β-amylase as a starch degrading enzyme.     

An evaluation of the use of 4-methylumbelliferyl-β-D-glucuronide (MUG) in different solid media for the detection and enumeration of Escherichia coli in foods

The use of 4-methylumbelliferyl-β- D -glucuronide (MUG) in different solid media for the detection and enumeration of Escherichia coli in foods was evaluated by testing the effects of different substrate concentrations (50 or 100 μg ml⁻¹), incubation temperatures (37 or 41·5°C) and incubation times (8, 12, 24 and 48 h). Different kinds of foods, both naturally and artificially contaminated, were analysed. The use of selective media without differential substances and an incubation time of 24 h seem to be worthy of recommendation. In this case an incubation temperature of 37°C would be preferred and the MUG concentration could be reduced to 50 μg ml⁻¹. Incubation times shorter than 24 h, which may cause a loss of sensitivity, require higher incubation temperatures (41·5°C) and MUG concentration (100 μg ml⁻¹).     

Subject index volume 144

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.     

Methyl 3β-(4-[125I]Iodophenyl)Tropane-2β-Carboxylate In Vitro Binding to Dopamine and Serotonin Transporters Under "Physiological" Conditions

Abstract: Methyl 3β-(4-[¹²⁵I]iodophenyl)tropane-2β-carboxylate ([¹²³I]β-CIT) is a single photon emission computed tomographic radiotracer for in vivo labeling of dopamine (DA) and serotonin (5-HT) transporters. Single photon emission computed tomographic experiments in nonhuman primates showed that [¹²³I]β-CIT in vivo binding to DA transporters had a much slower washout than binding to 5-HT transporters. This observation was not predicted from previously published in vitro studies. These studies, performed at 22°C in nonphysiological buffer, reported similar affinity of [¹²⁵I]β-CIT for DA and 5-HT transporters. We now report [¹²⁵I]β-CIT binding parameters to fresh rat membranes at 22°C and 37°C, in a buffer mimicking the composition of cerebrospinal fluid. At both temperatures, binding to DA transporters was best fit by a twosite model, whereas binding to 5-HT transporters was compatible with one population of sites. At 22°C, [¹²⁵I]β-CIT showed similar affinity to high-affinity DA (0.39 n M ) and 5-HT transporter sites (0.47 n M ). Increasing the incubation temperature from 22°C to 37°C reduced binding to DA transporters by 60%, whereas binding to 5-HT transporters was only marginally affected. In vitro kinetic experiments failed to detect significant differences in on or off rates that could explain the observed in vivo kinetics. These experiments thus failed to explain [¹²³ I]β-CIT in vivo uptake kinetics, suggesting the existence of specific factors affecting the in vivo situation.     

PROPERTIES OF MEMBRANE-BOUND DOPAMINES-HYDROXYLASE IN CHROMAFFIN GRANULES FROM BOVINE ADRENAL MEDULLA

Abstract— Properties of membrane-bound and soluble dopamine-β-hydroxylase were studied. Both enzyme forms have identical affinities for tyramine as the substrate. Arrhenius plots of the membrane-bound activity displayed a discontinuity at 29°C, the activation energy changing from 20,500 cal/mol below 29°C to 9500 cal/mol above 29°C. The soluble enzyme, like the purified enzyme, did not show discontinuities in Arrhenius plots, the activation energies being 18,500 cal/mol and 16,500 cal/mol respectively. The membrane-bound enzyme showed a discontinuity in the p K^m for tyramine versus reciprocal temperature plot, with a transition at 29°C, whereas the soluble enzyme failed to show such transition.
The membrane-bound dopamine-β-hydroxylase is solubilized by Triton X-100 as well as by lysolecithin. Of lecithin, lysophosphatidyl ethanolamine and phosphatidyl serine, lysolecithin was the only phospholipid to induce solubilization of membrane-bound dopamines β-hydroxylase. The 29°C-transition was not removed by treatment either with lysolecithin or with Triton X-100 used at concentration of up to 2%. This could indicate a solubilization of dopamine-β-hydroxylase with an associated lipid moiety which cannot be dispersed from the enzyme molecule and which still affects the activation energy and Michaelis constant for tyramine.
Results are discussed in terms of the relationship between lipid organization and enzyme activities; the significance of the solubilization by lysolecithin during exocytosis is considered in terms of the exocytosis process and fate of the chromaffin granule.     

Biochemical characterization of a β-fructofuranosidase from Rhodotorula dairenensis with transfructosylating activity

An extracellular β-fructofuranosidase from the yeast Rhodotorula dairenensis was characterized biochemically. The enzyme molecular mass was estimated to be 680 kDa by analytical gel filtration and 172 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, of which the N -linked carbohydrate accounts for 16% of the total mass. It displays optimum activity at pH 5 and 55–60 °C. The enzyme shows broad substrate specificity, hydrolyzing sucrose, 1-kestose, nystose, leucrose, raffinose and inulin. Although the main reaction catalyzed by this enzyme is sucrose hydrolysis, it also exhibits transfructosylating activity that, unlike other microbial β-fructofuranosidases, produces a varied type of prebiotic fructooligosaccharides containing β-(2→1)- and β-(2→6)-linked fructose oligomers. The maximum concentration of fructooligosaccharides was reached at 75% sucrose conversion and it was 87.9 g L⁻¹. The 17.0% (w/w) referred to the total amount of sugars in the reaction mixture. At this point, the amounts of 6-kestose, neokestose, 1-kestose and tetrasaccharides were 68.9, 10.6, 2.6 and 12.7 g L⁻¹, respectively.     

Isolation and properties of free and immobilized β-galactosidase from the psychrotrophic enterobacterium Buttiauxella agrestis (strain NC4)

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.     

Purification and characterization of an endoamylase from tulip (Tulipa gesneriana) bulbs

Amylase activity extracted from tulip ( Tulipa gesneriana L. cv. Apeldoorn) bulbs that had been stored for 6 weeks at 4°C was resolved to 3 peaks by anion-exchange chromatography on diethylaminoethyl-Sephacel. These 3 amylases exhibited different relative mobilities during non-denaturing polyacrylamide gel electrophoresis (PAGE). The most abundant amylase form (amylase I) was purified to apparent homogeneity using hydrophobic interaction chromatography, gel filtration and chromatofocusing. The apparent molecular mass of the purified amylase was estimated to be 51 kDa by sodium dodecyl sulfate-PAGE and 45 kDa by gel filtration chromatography. The purified amylase was determined to be an endoamylase (EC 3.2.1.1) based on substrate specificity and end-product analysis. The enzyme had a pH optimum of 6.0 and a temperature optimum of 55°C. The apparent K_m value with soluble starch (potato) was 1.28 mg ml⁻¹. The presence of Ca²⁺ increased the activity and thermal stability of the enzyme. The presence of dithiothreitol enhanced the activity, while β -mercaptoethanol and reduced glutathione had no significant effect. When pre-incubated in the absence of the substrate, N-ethylmaleimide and 5,5'-dithiobis-(2-nitrobenzoic acid) partially inhibited the enzyme. α -cyclodextrins or β -cyclodextrins had no effect on enzyme activity up to 10 m M . In addition to CaCl₂, CoCl₂ slightly enhanced activity, while MgCl₂ and MnCl₂ had no significant effect at a concentration of 2 m M . ZnCl₂, CuSO₄, AgNO₃ and EDTA partially inhibited enzyme activity, while AgNO₃ and HgCl₂ completely inhibited it at 2.0 m M .     

Purification and characterization of cellulolytic enzymes produced by Aspergillus nidulans

Three exo-glucanases, two endo-glucanases and two β-glucosidases were separated and purified from the culture medium of Aspergillus nidulans. The optimal assay conditions for all forms of cellulase components ranged from pH 5.0 to 6.0 and 50°C and 65°C for exo-glucanases and endo-glucanases but 35°C and 65°C for β-glucosidases. A close relation of enzyme stability to their optimal pH range was observed. All the cellulase components were stable for 10 min at 40–50°C. Exo-II and Exo-III ( K _m, 38.46 and 37.71 mg/ml) had greater affinity for the substrate than Exo-I ( K _m, 50.00 mg/ml). The K _m values of Endo-I and Endo-II (5.0 and 4.0 mg/ml) and their maximum reaction velocities ( V _max, 12.0 and 10.0 IU/mg protein) were comparable. β-Glucosidases exhibited K _m values of 0.24 and 0.12 mmol and V _max values of 8.00 and 0.67 IU/mg protein. The molecular weights recorded for various enzyme forms were: Exo-I, 29000; Exo-II, 72500; Exo-III, 138000; Endo-I, 25000; Endo-II, 32500; β-Gluco-I, 14000 and β-Gluco-II, 26000. Exo- and endo-glucanases were found to require some metal ions as co-factors for their catalytic activities whereas β-glucosidases did not. Hg²⁺ inhibited the activity of all the cellulase components. The saccharification studies demonstrated a high degree of synergism among all the three cellulase components for hydrolysis of dewaxed cotton.     

Detection of β-galactofuranosidase production by Penicillium and Aspergillus species using 4-nitrophenyl β-D-galactofuranoside

An assay was developed for detecting β-galactofuranosidase produced by Penicillium and Aspergillus spp. The substrate for the assay, 4-nitrophenyl β-D-galactofura-noside, was synthesized from penta-O-acetyl-β-D-galactofuranose and 4-nitrophenol by a tin chloride catalyzed reaction followed by O-deacetylation. Aspergillus spp. produced only small quantities of β-galactofuranosidase during 30 d at 25°C. Only the biverticillate Penicillium spp. ( P. funiculosum, P. islandicum, P. rubrum and P. tardum ) produced substantial β-galactofuranosidase after 1–4 weeks at 25°C. No extracellular antigens of these four Penicillium spp. could be detected in culture filtrates by the sandwich ELISA technique when antibodies to the extracellular β-galactofuranoside-containing polysaccharide antigen of P. digitatum was used. Antigens to all other Penicillium and Aspergillus spp. were easily detected in their culture filtrates.     

Purification and characterization of a β-glucosidase from the phytopathogenic fungus Fusarium oxysporum f. sp. melonis

T.M. ALCONADA AND M.J. MARTÍNEZ. 1996. Fusarium oxysporum f. sp. melonis produces cellulase and β-glucosidase activities in a medium with glucose and avicel as carbon source. A β-glucosidase from this crude material was purified by gel filtration and ion exchange chromatography successively. This enzyme is a unique band of protein in SDS-PAGE and isoelectric focussing. It had a molecular weight of 66000 and a pI of 5. Using p -nitrophenyl-β-D-glucopyranoside as substrate β-glucosidase shows a K _m of 210 μmol 1^-1, an optimum pH of 5.5 and an optimum reaction temperature of 60°C, being stable in a pH range of 5–7 for 48 h at room temperature.     

LOW-TEMPERATURE-INDUCED SYNTHESIS OF α-CAROTENE IN THE MICROALGA DUNALIELLA SALINA (CHLOROPHYTA)

The microalga Dunaliella salina (Teo.) is well known as an accumulator of β-carotene (β,β-carotene) when subjected to growth-limiting conditions (e.g. exposure to high irradiances). In addition, the carotenoid α-carotene (β,ε-carotene) may also be synthesized and subsequently accumulated by this alga under specific growth conditions. The main factor in stimulating the synthesis of this carotene was determined to be exposure to lower than optimum temperatures for algal growth. A 7.5-fold increase in the levels of α-carotene was observed when the temperature was decreased from 34 to 17° C, whilst levels of β-carotene were unaltered. The accumulation of α-carotene was unaffected by irradiance, although its isomeric composition was greatly altered by light levels. The proportion of 9- cis α-carotene increased from 15% to 45% of total α-carotene when the irradiance was decreased from 260 to 50 μmol·m⁻²·s⁻¹. Exposure to higher irradiances had little influence on the isomeric composition of this carotenoid. A reduction in growth temperature did not influence the isomeric composition of α-carotene. Nutrient status (nitrogen and phosphate) had no effect on either the content or isomeric composition of α-carotene accumulated by D. salina.     

Temperature modulates the cell wall mechanical properties of rice coleoptiles by altering the molecular mass of hemicellulosic polysaccharides

The present study was conducted to investigate the mechanism inducing the difference in the cell wall extensibility of rice ( Oryza sativa L. cv. Koshihikari) coleoptiles grown under various temperature (10–50°C) conditions. The growth rate and the cell wall extensibility of rice coleoptiles exhibited the maximum value at 30–40°C, and became smaller as the growth temperature rose or dropped from this temperature range. The amounts of cell wall polysaccharides per unit length of coleoptile increased in coleoptiles grown at 40°C, but not at other temperature conditions. On the other hand, the molecular size of hemicellulosic polysaccharides was small at temperatures where the cell wall extensibility was high (30–40°C). The autolytic activities of cell walls obtained from coleoptiles grown at 30 and 40°C were substantially higher than those grown at 10, 20 and 50°C. Furthermore, the activities of (1→3),(1→4)- β -glucanases extracted from coleoptile cell walls showed a similar tendency. When oat (1→3),(1→4)- β -glucans with high molecular mass were incubated with the cell wall enzyme preparations from coleoptiles grown at various temperature conditions, the extensive molecular mass downshifts were brought about only by the cell wall enzymes obtained from coleoptiles grown at 30–40°C. There were close correlations between the cell wall extensibility and the molecular mass of hemicellulosic polysaccharides or the activity of β -glucanases. These results suggest that the environmental temperature regulates the cell wall extensibility of rice coleoptiles by modifying mainly the molecular mass of hemicellulosic polysaccharides. Modulation of the activity of β -glucanases under various temperature conditions may be involved in the alteration of the molecular size of hemicellulosic polysaccharides.     

The effect of incubation temperature and sodium chloride concentration on the growth kinetics of Vibrio anguillarum and Vibrio anguillarum-related organisms

The effect of temperature and NaCl concentration on the growth kinetics of Vibrio anguillarum and V. anguillarum -related (VAR) strains was studied.
For one wild VAR strain, NaCl concentration interfered with growth temperature parameters, in particular, with the maximum growth temperature but also with the optimum temperature (defined as the temperature at which μ_max equals its maximal value μ_opt), and with μ_opt itself. For the same strain, optimal growth required the adding of NaCl to the medium to a final concentration of 1·5%. These results were not confirmed by tests on a V. anguillarum collection strain.
When the NaCl concentration in the culture media was 1.5%, the optmum temperature for the nine strains studied ranged from 29.7°C to 34°C whereas the maximum temperature ranged between 35.3°C and 38.5°C.
Hence, antbiotic susceptibility testing as well as biochemical identification might be carried out at 30°C in the presence of 1.5% NaCl, which corresponded to a suboptimal growth.     

On the monoterpene emission under heat stress and on the increased thermotolerance of leaves of Quercus ilex L. fumigated with selected monoterpenes

Leaves of the monoterpene emitter Quercus ilex were exposed to a temperature ramp with 5 °C steps from 30 to 55 °C while maintained under conditions in which endogenous emission of monoterpenes was allowed or suppressed, or under fumigation with selected exogenous monoterpenes. Fumigation with monoterpenes reduced the decline of photosynthesis, photorespiration and monoterpene emission found in non-fumigated leaves exposed to high temperatures. It also substantially increased respiration when photosynthesis and photorespiration were inhibited by low O₂ and CO₂-free air. These results indicate that, as previously reported for isoprene, monoterpenes may help plants cope with heat stress. Monoterpenes may enhance membrane stability, thus providing a rather non-specific protection of photosynthetic and respiratory processes. Monoterpene emission was maximal at a temperature of 35 °C and was inhibited at higher temperatures. This is likely to be the result of the temperature dependency of the enzymes involved in monoterpene synthesis. In contrast to other monoterpenes, cis- and trans- β -ocimene did not respond to exposure to high temperatures. Cis- β -ocimene also did not respond to low O₂ or to fumigation. These results indicate that cis and trans- β -ocimene may have a different pathway of formation that probably does not involve enzymatic synthesis.     

Temperature-dependent changes in Photosystem II heterogeneity of attached leaves under high light

Attached leaves of pumpkin ( Cucurbita pepo L. cv. Jattiläismeloni) were exposed to high light intensity at room temperature (ca 23°C) and at 1°C. Fluorescence parameters and electron transport activities measured from isolated thylakoids indicated faster photoinhibition of PSII at low temperature. Separation of the α and β components of the complementary area above the fluorescence induction curve of dichlorophenyl-dimethylurea-poisoned thylakoids revealed that at low temperature only the α-centers declined during exposure to high light intensity while the content of functional β-centers remained constant. Freeze-fracture electron microscopy showed no decrease in the density of particles on the appressed exoplasmic fracture face, indicating that the photoinhibited α-centers remained in the appressed membranes at 1°C. Because of the function of the repair and protective mechanisms of PSII, strong light induced less photoinhibition at room temperature, but more complicated changes occurred in the α/β-heterogeneity of PSII. During the first 30 min at high light intensity the decrease in α-centers was almost as large as at 1°C, but in contrast to the situation at low temperature the decrease in α-centers was compensated for by a significant increase in PSIIβ-centers. Changes in the density and size of freeze-fracture particles suggest that this increase in β-centers was due to migration of phosphorylated light-harvesting complex from appressed to non-appressed thylakoid membranes while the PSII core remained in the appressed membranes. This situation, however, was only transient and was followed by a rapid decrease in the functionalβ-centers.     

An enzyme system hydrolysing the polysaccharides of Xanthomonas species

Enzymes hydrolysing the exopolysaccharides of Xanthomonas campestris and related species (xanthan) have been obtained from a Bacillus species isolated by enrichment culture. Growth on xanthan induced a number of enzymes acting on the xanthan molecule. These included one or more β-glucanohydrolases and β-glucosidases, together with mannosidases. The former activities were also present in cultures grown in the presence of laminaran or scleroglucan, but not in simple synthetic media with glucose as substrate. Partial purification of the enzymes active on glucans was achieved by ammonium sulphate precipitation and chromatography on DEAE-sepharose and CM-sepharose. The specificity of the β-glucosidase and the β-glucanohydrolase were investigated. Several β-glucans were hydrolysed to glucose and disaccharides, but there was no activity against β→ 6 linked polymers, cellulose azure or microcrystalline cellulose. Carboxymethylcellulose was hydrolysed, as were laminaran, scleroglucan and pachyman. Activity was greater against the β→ 4 linked glucans than against the β→ 3 linked glucans tested. As periodate-oxidized laminarin was also hydrolysed, it was concluded that the glucanohydrolase acted as an endo enzyme. The β-glucosidase had a pH optimum at about 8–2 and a temperature optimum at 45°C; it showed higher activity against o -nitrophenyl-D-glucopyranoside, cellobiose, trehalose and sophorose than against gentibiose.     

Extracellular enzyme activities associated with epiphytic microbiota on submerged stems of the reed Phragmites australis

Abstract Fluorogenic 4-methylumbelliferyl (MUF) compounds were used as analogue substrates for assay of extracellular enzyme activities associated with epiphytic microbiota at submerged Phragmites australis stem surfaces. Incubations at a range of MUF substrate concentrations indicated that saturation of enzyme activity was achieved at a MUF substrate concentration of about 200 μmol 1⁻¹. Later determinations at a single, saturation, concentration of MUF substrate were, therefore, carried out at about 200 μmol l⁻¹. Such determinations were undertaken using P. australis stems from eight gravel-pit ponds. The rate of enzymatic hydrolysis of MUF phosphate (analogue substrate for phosphatase activity) was > MUF β- d -glucopyranoside (β- d -glucosidase) > MUF β- d -galactopyranoside (β- d -galactosidase) > MUF sulphate (sulphatase) and MUF palmitate (lipase) on stems from all eight ponds. Thus the relative magnitude of the various components of total epiphyton extracellular enzyme activity might be a conservative feature.