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Showing papers on "Aspergillus niger published in 1985"


Journal ArticleDOI
TL;DR: A general, simple and inexpensive method for the isolation of DNA from filamentous fungi, starting from freeze‐dried mycelium 01–015% by weight, which allows the processing of many samples in parallel.
Abstract: We describe a general, simple and inexpensive method for the isolation of DNA from filamentous fungi. Starting from freeze-dried mycelium 01–015% by weight can be isolated as high molecular weight DNA suitable for restriction and ligation in 2 h. The preparation can be done in Eppendorf tubes and allows the processing of many samples in parallel. We have used the method with the basidiomycetes Phanerochaete chrysosporium, Coprinus cinereus and the ascomycete Aspergillus nidulans and others have used it with Trichoderma reesei, Aspergillus niger and for the isolation of DNA from tomato plants.

1,676 citations


Journal ArticleDOI
TL;DR: A transformation system is developed for Aspergillus niger using the amdS gene as a dominant heterologous marker for selecting transformants on the basis of acetamide utilization and it is shown that an unselected plasmid can be co‐transformed with the amdR/intA plasmids into A. niger.
Abstract: Aspergillus niger grows poorly on acetamide as a nitrogen or carbon source and lacks sequences detectably homologous to the amdS gene encoding the acetamidase of Aspergillus nidulans. We have taken advantage of these observations to develop a transformation system for A. niger using the amdS gene as a dominant heterologous marker for selecting transformants on the basis of acetamide utilization. Transformants varied in their ability to grow on amide media and the number of integrated copies of the amdS plasmid ranged from 1 or 2 to greater than 100. Southern analysis of transformants revealed that the multiple copies were integrated into the chromosome in tandem arrays. This result indicates that transformation of A. niger is more similar to mammalian cells than to yeast. Analysis of enzyme activity levels and RNA levels showed that most of the copies of amdS were expressed. Mitotic stabilities of transformants were found to be high. A transformant containing greater than 100 copies of the amdS gene was impaired in omega-amino acid utilization, a result that has also been found in A. nidulans. Since, in A. nidulans, omega-amino acids induce acetamidase via a characterizied regulatory gene (amdR/intA) this observation implies that titration of an analogous A. niger regulatory gene product by multiple amdS copies has occurred. Additional evidence suggested that the amdS gene is regulated in A. niger. It has also been shown that an unselected plasmid can be co-transformed with the amdS plasmid into A. niger.

437 citations


Journal ArticleDOI
01 Jan 1985-Gene
TL;DR: A mutant of Aspergillus niger defective in ornithine transcarbamylase function was transformed with plasmids carrying a functional copy of the argB gene of As pergilli nidulans after treatment of spheroplasts in the presence of polyethylene glycol and calcium ions to insert any gene into the genome of A. niger.

130 citations


Journal ArticleDOI
TL;DR: In this paper, the degradation of chlorsulfuron was evaluated using plant bioassay and high-performance liquid chromatography (HPLC) radiotracer techniques.
Abstract: Degradation of chlorsulfuron {2-chloro-N- (((4- methoxy- 6- methyl-1,3 ,5 -triazin-yl)amino) carbonyl) benzene- sulfonamide} in acidic and alkaline soils was evaluated using plant bioassay and high-performance liquid chromatography (HPLC) radiotracer techniques. Soil sterilization with either ethylene oxide (EtO) or gamma irradiation significantly reduced breakdown of chlorsulfuron; the ability for degrada- tion was restored by reinoculation with indigenous soil micro- organisms. Streptomyces griseolus (a soil actinomycete), Aspergillus niger, and Penicillium sp. (soil fungi) were demon- strated to degrade 14C-chlorsulfuron in pure culture. In addition to microbial breakdown, chemical hydrolysis was an important factor in the disappearance of chlorsulfuron from soil. The contribution of chemical hydrolysis to total degradation was a function of soil pH, with hydrolysis oc- curring most rapidly in acidic soils. Both dissipation processes slowed markedly at low temperatures. Additional index words. Soil pH, soil temperature, soil mois- ture, Streptomyces griseolus, Aspergillus niger, Penicillium

110 citations


Journal ArticleDOI
TL;DR: Two endo‐xylanases were purified to homogeneity from a crude Aspergillus niger pentosanase preparation and their low activity on a linear xylooligosaccharide mixture and absence of activity on insoluble xylan freed of branches suggest that the xylanases require a branch point nearby for significant attack.
Abstract: Two endo-xylanases (1,4-beta-D-xylan xylanohydrolase, EC 3.2.1.8) were purified to homogeneity from a crude Aspergillus niger pentosanase preparation by Ultrogel AcA 54 gel permeation chromatography, SP-Sephadex C-25 cation exchange chromatography at pH 4.5, Sephadex G-50 gel permeation chromatography, and a second SP-Sephadex C-25 step, this one at pH 5.8. The two xylanases hydrolyzed soluble xylan more rapidly than insoluble branched xylan, but attacked each substance to an equal extent. Their low activity on a linear xylooligosaccharide mixture and absence of activity on insoluble xylan freed of branches suggest that the xylanases require a branch point nearby for significant attack. No xylose or L-arabinose was produced, the major products of low molecular weight being tri- and pentasaccharides and smaller amounts of di-, tetra-, and hexasaccharides. There was low activity on untreated and crystalline cellulose and on carboxymethylcellulose and no activity on other polysaccharides tested. These two xylanases had molecular weights of ca. 1.3 x 10(4) and similar amino acid profiles, high in acidic and low in sulfur-containing residues. Isoelectric points were 8.6 for I and 9.0 for II. Optimum pH values for activity were 6.0 and 5.5, respectively. In a 20-min assay at pH 5.5, each was most active at 45 degrees C, with activation energies up to 40 degrees C of 30.4 and 38.8 kJ/ mol, respectively. Optimum pH levels for stability were 5.0 and 6.0, with half-lives at 60 degrees C and those pHs of 20 and 75 min, respectively.

84 citations


Journal ArticleDOI
TL;DR: The formation and location of glucose oxidase was studied in Aspergillus niger, which was pregrown under citric acid producing conditions and could be “de novo” induced by a shift in pH from 1.7 to 5.5.
Abstract: The formation and location of glucose oxidase was studied in Aspergillus niger, which was pregrown under citric acid producing conditions. Glucose oxidase could be “de novo” induced by a shift in pH from 1.7 to 5.5. The induction required the intracellular presence of either glucose or glucose-6-phosphate. Glucose oxidase so produced was rapidly secreted into the medium, which was not due to autolysis.

80 citations


Journal ArticleDOI
TL;DR: Growth and sterol synthesis of Aspergillus fumigatus and A. niger were studied in control cultures and in the presence of ketoconazole or itraconazole, the latter compound being 100 times more growth inhibitory than the former.
Abstract: Growth and sterol synthesis of Aspergillus fumigatus and A. niger were studied in control cultures and in the presence of ketoconazole or itraconazole, the latter compound being 100 times more growth inhibitory than the former. Sterol synthesis is inhibited more rapidly than any visible fungal outgrowth. This inhibition results in an accumulation of 4,14 dimethyl- and 4,4',14 trimethylsterols. The presence of these membrane-disturbing sterols may result in a pertubation of membrane-bound enzyme systems such as chitin synthase.

65 citations


Journal ArticleDOI
TL;DR: The possibility that citric acid accumulation is caused by oxaloacetate and NADH inhibition of the alpha-ketoglutarate dehydrogenase of A. niger is discussed.
Abstract: alpha-Ketoglutarate dehydrogenase has been demonstrated for the first time in cell extracts from the filamentous fungus Aspergillus niger. A minimum protein concentration of 5 mg/ml is necessary for detecting enzyme activity, but a maximum of ca. 0.060 mumol/min per mg of protein is observed only when the protein concentration is above 9 mg/ml. alpha-Ketoglutarate can partly stabilize the enzyme against dilution in the assay system. Neither bovine serum albumin nor a variety of substrates or effectors of the enzyme could stabilize the enzyme against inactivation by dilution. A kinetic analysis of the enzyme revealed Michaelis-Menten kinetics with respect to alpha-ketoglutarate, coenzyme A, and NAD. Thiamine PPi was required for maximal activity. NADH, oxaloacetate, succinate, and cis-aconitate were found to inhibit the enzyme; AMP was without effect. Monovalent cations including NH4+ were inhibitory at high concentrations (greater than 20 mM). The highest enzyme activity was found in rapidly growing mycelia (glucose-NH4+ or glucose-peptone medium). We discuss the possibility that citric acid accumulation is caused by oxaloacetate and NADH inhibition of the alpha-ketoglutarate dehydrogenase of A. niger.

63 citations


Journal ArticleDOI
TL;DR: Xylanase synthetized in solid fermentation is a little more thermostable than that from liquid fermentation and is maximally active at 50° C, compared to 45° C for enzyme from liquid culture.
Abstract: Xylanase production by Aspergillus niger van Tieghem was studied in solid-state cultivation. The screening of substrates was carried out in column incubators aerated with humidified air at 30°C. Results of physiological studies showed that the best yield of xylanase was 2500 U/g dry matter on a mixture of straw+bran 1:1 at 70% of moisture content.

63 citations


Journal ArticleDOI
TL;DR: Resting cells of bacteria grown in the presence of diphenylmethane oxidized substituted analogs such as 4-hydroxydiphenyl methane, bis(4-Hydroxyphenyl)methanes, bis (4-chlorophenyl)Methane (DDM), benzhydrol, and 4,4'-dichlorobenzhydrol to 4-chlorobenzophenone and a methylated 4- chlorobenzone.
Abstract: Resting cells of bacteria grown in the presence of diphenylmethane oxidized substituted analogs such as 4-hydroxydiphenylmethane, bis(4-hydroxyphenyl)methane, bis(4-chlorophenyl)methane (DDM), benzhydrol, and 4,4'-dichlorobenzhydrol. Resting cells of bacteria grown with benzhydrol as the sole carbon source oxidized substituted benzhydrols such as 4-chlorobenzhydrol, 4,4'-dichlorobenzhydrol, and other metabolites of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT), such as DDM and bis(4-chlorophenyl)acetic acid. Bacteria and fungi converted 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane to 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane, DDM, 4,4'-dichlorobenzhydrol, and 4,4'-dichlorobenzophenone. Aspergillus conicus converted 55% of bis(4-chlorophenyl)acetic acid to unidentified or unextractable water-soluble products. Aspergillus niger and Penicillium brefeldianum converted 12.4 and 24.6%, respectively, of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane to water-soluble and unidentified products. 4-Chlorophenylacetic acid, a product of ring cleavage, was formed from DDM by a false smut fungus of rice. A. niger converted 4,4'-dichlorobenzophenone to 4-chlorobenzophenone and a methylated 4-chlorobenzophenone.

59 citations


Journal ArticleDOI
TL;DR: Living Aspergillus niger cells were entrapped in polyacrylamide gels and employed in both replacement batch and continuous column bioreactors to produce citric acid from sucrose.
Abstract: Living Aspergillus niger cells were entrapped in polyacrylamide gels and employed in both replacement batch and continuous column bioreactors to produce citric acid from sucrose. With the replacement batch bioreactor, increase of citric acid was observed under conditions of higher aeration and of wider surface of immobilized cells. With the continuous bioreactor, the maximum citric acid yield was 39.1 mg/h per 40 g gels. The biocatalyst activity or half-life was 105 days.

Patent
04 Dec 1985
TL;DR: In this paper, a DNA vector containing a selectable marker which is capable of incorporation into the DNA of the host A. niger cells, but which is not to be found in the A.niger cells prior to this transformation, is used for modified expression.
Abstract: Transformants of Aspergillus niger and related Aspergilli, containing foreign DNA conferring modified properties of expression thereon, are prepared by use of a DNA vector which contains a selectable marker which is capable of incorporation into the DNA of the host A. niger cells, but which is not to be found in the A. niger cells prior to this transformation. The vector also contains other foreign DNA to be incorporated into the A. niger, for modified expression. The process suitably uses mutants of A. niger as hosts, the mutants lacking the selectable marker as compared with wild-type A. niger, and conducts the transformation on spheroplasts of A. niger.

Journal ArticleDOI
TL;DR: A homogeneous endo-xylanase (1,4‐β‐D‐xylan xylanohydrolase, EC 3.8) was obtained from a crude Aspergillus niger pentosanase by chromatography, yielding large amounts of unreacted xylan and a mixture of oligosaccharides with chain lengths from two to six, much more active on soluble than on insoluble xylan.
Abstract: A homogeneous endo-xylanase (1,4-..beta..-D-xylan xylano-hydrolase, EC 3.2.1.8) was obtained from a crude Aspergillus niger pentosanase by chromatography with Ultrogel AcA 54, SP-Sephadex C-25 at pH 4.5, DEAE-Sephadex A-25 at pH 5.4, Sephadex G-50, and SP-Sephadex C-25 with a gradient from pH 2.8 to pH 4.6. It was much more active on soluble than on insoluble xylan yielding large amounts of unreacted xylan and a mixture of oligosaccharides with chain lengths from two to six. No xylose or L-arabinose was produced. There was high activity on a xylopentaose through xylononaose mixture, but not on xylobiose, xylotriose, or xylotetraose. The enzyme had slight activity on untreated cellulose, carboxymethylcellulose, and pectin. Molecular weight was ca. 1.4 x 10/sup 4/, with an isoelectric point of 4.5 and an amino acid profile high in acidic but low in sulfur-containing residues. In a 25-min assay at pH 4.7, this endo-xylanase was most active at 45 degrees C, with an activation energy from 5 to 35 degrees C of 33.3 kJ/mol. The optimum pH for activity was 4.9. Decay in buffer was first order, with an activation energy at pH 4.7 from 48 to 53 degrees C of 460 kJ/mol. Optimum pH for stability was about 5.6,more » where the half-life at 48 degrees C in buffer was ca. 40 h.« less

Journal ArticleDOI
TL;DR: The effect of manganese deficiency on macromolecule synthesis has been studied in a citric acid producing strain of Aspergillus niger and addition of inhibitors of RNA, DNA or protein synthesis revealed that only emetine and cycloheximide successfully antagonized the adverse effect ofManganese ions oncitric acid accumulation.
Abstract: The effect of manganese deficiency on macromolecule synthesis has been studied in a citric acid producing strain of Aspergillus niger: pulse labelling experiments showed that the synthesis of both protein and RNA was not influenced by the presence of manganese; however, increased protein degradation occurred under manganese deficiency. This was also reflected by the increased activity of an intracellular proteinase activity under these conditions. In replacement cultures addition of inhibitors of RNA, DNA or protein synthesis revealed that only emetine and cycloheximide (which both act at the ribosome) successfully antagonized the adverse effect of manganese ions on citric acid accumulation. Manganese deficiency was also characterized by a decreased portion of polysomes and 80 S ribosomes.


Journal ArticleDOI
TL;DR: A qualitative screening revealed the occurrence of lipase, esterase, protease, amylase, endo-1,4-β-D-glucanase, xylanase, pectinmethylesterase and polygalacturonase activities in the technical Aspergillus niger enzyme under study.
Abstract: A qualitative screening revealed the occurrence of lipase, esterase, protease, amylase, endo-1,4-β-D-glucanase, xylanase, pectinmethylesterase, polygalacturonase, catalase, β-D-glucosidase and β-D-galactosidase activities in the technical Aspergillus niger enzyme under study (Lipase 2212 D, Rohm). The isolation and purification of lipolytic activities were performed by combination of DEAE-Trisacryl M ion exchange chromatography, Sephadex G 50 gel filtration and hydrophobic chromatography using Phenylsepharose CL-4B. The individual purification steps were checked by specific enzyme visualization in ultrathin agar gels after ultrathin-layer isoelectric focusing (UIEF). Two UIEF homogeneous lipase isoenzymes (I and II) were isolated and characterized by the following parameters: isoelectric points (I: 4.0; II. 3.5); molecular weights (I: 31000 daltons; II: 19000 daltons); carbohydrate contents (I: 6%; II: 9%) and compositions; pH optima (I, II: 5-6); substrate specificities and various effectors.

Journal ArticleDOI
TL;DR: Investigation into the source of the antigen showed that whereas, in some areas of the plant, A niger spores were present, in others there were no detectable spores, in these areas extracts of filters from air samplers were shown by RAST inhibition to contain A nigers antigens, indicating that the culture fluid was generating airborne antigen.
Abstract: The workforce at a biotechnology plant producing citric acid by fermentation of molasses with a strain of Aspergillus niger was studied. A combination of a respiratory questionnaire and clinical assessment identified 18 subjects (4.9% of the workforce) with work related bronchospasm. In nine of these evidence of sensitisation to A niger was obtained by skin prick tests and radioallergosorbent test (RAST) using as an antigen an extract of the A niger culture fluid from the process. Of the 325 subjects without work related bronchospasm, only nine (2.7%) had a positive prick test. There were no subjects with symptoms of extrinsic allergic alveolitis. Investigation into the source of the antigen showed that whereas, in some areas of the plant, A niger spores were present, in others there were no detectable spores. In these areas, however, extracts of filters from air samplers were shown by RAST inhibition to contain A niger antigens, indicating that the culture fluid was generating airborne antigen. RAST inhibition studies showed that the A niger culture fluid used in the process contained antigens that were not present in a commercially available A niger extract, thus emphasising the importance in this type of investigation of using antigens prepared from material to which the workers are exposed.

Journal ArticleDOI
TL;DR: A cellulolytic enzyme was extensively purified from a commercial crude cellulase preparation from Aspergillus niger by consecutive column chromatography and was characterized as an endocellulase on the basis of its action on carboxymethyl cellulose and cellooligosaccharides.
Abstract: A cellulolytic enzyme was extensively purified from a commercial crude cellulase preparation from Aspergillus niger by consecutive column chromatography. The purified enzyme was homogeneous on polyacrylamide gel as well as ampholine electrophoresis. The enzyme was an acidic protein with an isoelectric point at pH 3.67. The molecular weight of the enzyme was estimated to be 31,000 by SDS-polyacrylamide gel electrophoresis. No carbohydrate moiety seemed to be associated with the enzyme protein.The optimum pH was 4.0, and the optimum temperature of the enzyme was 45~50°C. The enzyme was completely stable over the range of pH 5.0~8.0 at 4°C for 24 hr, and retained about 50% of its original activity after heating at 70°C for 10 min. The enzyme was partly inactivated by 1 mm Ag+, Hg2+, and Fe2+.The enzyme was characterized as an endocellulase on the basis of its action on carboxymethyl cellulose and cellooligosaccharides. The enzyme split cellopentaose, retaining the β-configuration of the anomeric carbon atoms...

Journal ArticleDOI
TL;DR: Compared in vivo steady-state concentrations of citrate and isocitrate in Aspergillus niger grown under various citric acid-producing conditions strongly argue against an inhibition of aconitase duringcitric acid fermentation.
Abstract: In view of the often-cited theory that citric acid accumulation is caused by an inhibition of aconitase activity, the equilibrium of the reaction of aconitase was investigated by comparing in vivo steady-state concentrations of citrate and isocitrate in Aspergillus niger grown under various citric acid-producing conditions. With the equilibrium catalyzed by the A. niger enzyme in vitro, similar values were obtained. The validity of our in vivo measurements was verified by the addition of the aconitase inhibitor fluorocitrate, which appreciably elevated the citrate:isocitrate ratio. The results strongly argue against an inhibition of aconitase during citric acid fermentation.


Journal ArticleDOI
TL;DR: This study of the cellobiase activity of these two enzyme sources was undertaken as a first step in the formation of a kinetic model for cellulose hydrolysis that can be used in process design.
Abstract: The enzymatic hydrolysis of cellulose to glucose involves the formation of cellobiose as an intermediate. It has been found necessary to add cellobiase from Aspergillus niger (NOVO) to the cellobiase component of Trichoderma reesei mutant Rut C-30 (Natick) cellulase enzymes in order to obtain after 48 h complete conversion of the cellobiose formed in the enzymatic hydrolysis of biomass. This study of the cellobiase activity of these two enzyme sources was undertaken as a first step in the formation of a kinetic model for cellulose hydrolysis that can be used in process design. In order to cover the full range of cellobiose concentrations, it was necessary to develop separate kinetic parameters for high- and low-concentration ranges of cellobiose for the enzymes from each organism. Competitive glucose inhibition was observed with the enzymes from both organisms. Substrate inhibition was observed only with the A. niger enzymes.

Journal ArticleDOI
TL;DR: The study revealed different reaction mechanisms of the pectin deesterification by pECTin esterases from Aspergillus species and higher plants.
Abstract: By reaction of pectin esterase (PE) from Aspergillus niger and oranges as well as lye, with 95% esterified citrus and apple pectin we prepared series of preparations with degrees of esterification between 35 and 77%. In these partial deesterified pectins the form of distribution of the free and esterified carboxyl groups has been determined from the activity coefficient gamma Ca2+ of the calcium counterions in the solutions of the corresponding calcium pectinates, from the electrostatic free enthalpy delta (Gel/N)KCa of the ion exchange Ca2+----2K+ in these systems as well as from the relative activity of the polygalacturonase reacting with sodium pectinate. The PE from A niger hydrolyzes the esterified carboxyl groups more or less randomly, in a manner similar to the effect of lye on pectin. On the other hand PE from oranges brings about block-like groupings of free carboxyl groups in the pectin molecule. The study revealed different reaction mechanisms of the pectin deesterification by pectin esterases from Aspergillus species and higher plants.


Journal ArticleDOI
TL;DR: A simple kinetic model for the hydrolysis of starch by glucoamylase from Aspergillus niger and Rhizopus niveus was proposed, and it was found to have practical use.
Abstract: Kinetics of the condensation of glucose into maltose and isomaltose in the hydrolysis of starch by two types of glucoamylase (from Aspergillus niger and Rhizopus niveus) was studied both experimentally and theoretically. A kinetic model for the hydrolysis of starch by glucoamylase from A. niger was proposed. In this model the reversible hydrolysis of maltose and isomaltose and the kinetic parameters change were taken into consideration. Calculated values agreed approximately with the experimental results, and this simple kinetic model was found to have practical use. The rate of condensation of glucose into isomaltose by enzyme from A. niger was about three times larger than that by enzyme from R. niveus. At a higher initial concentration of starch a large amount of isomaltose was reversed, and the glucose yield was reduced significantly after very long reaction times.


Journal ArticleDOI
TL;DR: The mutant (UFA2) of Aspergillus niger contains a higher level of glycerides and lower levels of sterol (both free and esterified form), phospholipids, and glycolipids than the wild type.
Abstract: A comparative study of the mycelial lipid composition of a wild strain (V35) and one unsaturated fatty acid auxotroph (UFA2) of Aspergillus niger has been performed. The lipid composition of both strains are qualitatively the same but quantitatively different. All the strains contain the following phospholipids: cardiolipin, phosphatidylethanolamine, phosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylcholine, and phosphatidylserine; and triglycerides, diglycerides, mono-glycerides, ergosterol, and sterol esters as the neutral lipids; mono- and di-galactosyl diglyceride as the major glycolipids along with small amounts of the corresponding mannose analogs. Phosphatidylethanolamine and phosphatidylcholine constitute the bulk of the phospholipids. The mutant (UFA2) contains a higher level of glycerides and lower levels of sterol (both free and esterified form), phospholipids, and glycolipids than the wild type. Aspergillus niger contains C16 to C18 saturated and unsaturated fatty acids. Small...

Journal ArticleDOI
TL;DR: Plasma membranes were isolated by means of the concanavalin A technique from protoplasts of manganese deficient and sufficient grown mycelium with differences with respect to their quantitative contents of fatty acids, sterols and phospholipids.
Abstract: Plasma membranes were isolated by means of the concanavalin A technique from protoplasts of manganese deficient (< 10−8 M Mn2+) and sufficient (10−5 M Mn2+) grown mycelium. The membranes differed with respect to their quantitative contents of fatty acids, sterols and phospholipids. These changes did not influence the glucose transport system, as shown by kinetic investigations using intact mycelia.

Journal ArticleDOI
TL;DR: Several kinetic characteristics of a thermostable anthocyanin-β-glycosidase from Aspergillus niger have been evaluated and Glucono-deltalactone, gluconic acid, and glucose appeared to be competitive inhibitors of this enzyme.

Journal ArticleDOI
TL;DR: The pH activity of immobilized enzyme was unchanged, but exhibited more stable activity at acidic pH than the free enzyme, and higher resistance to heat inactivation was also observed.
Abstract: Aspergillus niger cellulase was imobilized on cyanogen bromide activated dextran of varying molecular weights. The effect of different concentrations of cyanogen bromide used for the activation process was also studied. About 50% conjugation and 70% retention activity was achieved in the immobilized cellulase. The pH activity of immobilized enzyme was unchanged, but exhibited more stable activity at acidic pH than the free enzyme. Higher resistance to heat inactivation was also observed.

Journal ArticleDOI
TL;DR: Galactose interfered with the glucose-repression of the key enzyme 2-oxoglutarate dehydrogenase, and caused inhibition of citric acid production, and also reduced the rate of glucose utilization.
Abstract: Previous work in this laboratory has demonstrated that although Aspergillus niger can readily utilize galactose, no citric acid is produced from this carbon source (Hossain et al 1984) Experiments were now conducted where galactose was added at various concentrations to synthetic growth medium containing glucose as carbon source, so that the effect of galactose on citric acid production from glucose could be observed The results showed that the presence of galactose or a product of galactose metabolism caused inhibition of citric acid production, and also reduced the rate of glucose utilization Enzyme analyses using mycelial cell-free extracts indicated that galactose interfered with the glucose-repression of the key enzyme 2-oxoglutarate dehydrogenase