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H Verachtert

Publications and source records attributed to H Verachtert.

At least 37 records · Page 2Linked to original sources
PubMed1993

Parameters affecting the degradation of benzothiazoles and benzimidazoles in activated sludge systems.

It was found that benzothiazole, 2-oxybenzothiazole and 2-benzothiazolesulphonate were degraded in activated sludge systems. 2-Mercaptobenzothiazole (MBT) was more resistant, although the first step in MBT degradation seemed to be transformation to the sulphonate form. At higher MBT concentrations, it was transformed into a disulphide, which accumulated in the sludge. MBT was also found to be mainly responsible for the toxicity of rubber chemical waste-water towards activated sludges. It inhibited the degradation of the other heterocycles. Only at concentrations of around 20 ppm was MBT degraded. Mercaptobenzimidazole ranked second in resistance to degradation.

Benzimidazoles↗
PubMed1993

Localization and Characterization of alpha-Glucosidase Activity in Brettanomyces lambicus.

Brettanomyces lambicus was isolated and identified from a typical overattenuating Belgian lambic beer and exhibited extracellular and intracellular alpha-glucosidase activities. Production of the intracellular enzyme was higher than production of the extracellular enzyme, and localization studies showed that the intracellular alpha-glucosidase is mostly soluble and partially cell wall bound. Both intracellular and extracellular enzymes were purified by ammonium sulfate precipitation, gel filtration (Sephadex G-150, Sephadex G-200, Ultrogel AcA-44), and ion-exchange chromatography (sulfopropyl-Sephadex C-50, (carboxymethyl-Sephadex C-50). The intracellular alpha-glucosidase exhibited optimum activity at 39 degrees C and pH 6.2. The extracellular enzyme exhibited optimum catalytic activity at 40 degrees C and pH 6.0. The molecular masses of purified intracellular and extracellular alpha-glucosidases, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, were 72,500 and 77,250, respectively. For both enzymes there was a decrease in the rate of hydrolysis with an increase in the degree of polymerization, and both enzymes hydrolyzed dextrins isolated from lambic wort (degrees of polymerization, 3 to 9 and more than 9). The K(m) values for p-nitrophenyl-alpha-d-glucopyranoside, maltose, and maltotriose for the intracellular enzyme were 0.9, 3.4, and 3.7 mM, respectively. The K(i) values for both enzymes were between 28.5 and 57 muM for acarbose and between 7.45 and 15.7 mM for Tris. These enzymes are probably involved in the overattenuation of spontaneously fermented lambic beer.

Journal Article↗
PubMed1987

Purification and characterization of extracellular alpha-amylase and glucoamylase from the yeast Candida antarctica CBS 6678.

An alpha-amylase and a glucoamylase were purified to homogeneity from the culture fluid of beta-cyclodextrin-grown Candida antarctica CBS 6678 by protamine sulfate treatment, ammonium sulfate precipitation, gel filtration (Sephadex G-75 sf, Ultrogel AcA 54), DEAE-Sephacel chromatography, hydroxyapatite chromatography and affinity chromatography on acarbose--AH-Sepharose 4B. Both enzymes were monomeric glycoproteins with fairly different amino acid compositions. Their apparent relative molecular mass, sedimentation coefficient (Szero20,w), isoelectric point, absorption coefficient (280 nm), pH and temperature optima were estimated as 48,500, 4.7 S, 10.1, 1.74 cm2 mg-1, 4.2 and 57 degrees C, respectively, for glucoamylase and as 50,000, 4.9 S, 10.3, 1.53 cm2 mg-1, 4.2 and 62 degrees C, respectively, for alpha-amylase. Kinetic analyses indicated that both enzymes preferentially hydrolyzed high-molecular-mass substrates, including some raw starches. alpha-Amylase was active on cyclodextrins, whereas debranching activity was demonstrated for glucoamylase. Trestatins were potent inhibitors of both alpha-amylase (Ki less than 1 microM) and glucoamylase (Ki less than 0.1 microM), being more effective than Bay e 4609 (Ki less than 10 microM). Glucoamylase was selectivity and strongly inhibited by acarbose (Ki less than 0.1 microM). Activity of the latter enzyme was also affected by 1-deoxynojirimycin (Ki less than 1 mM), maltitol and amino alcohols (Ki less than 10 mM). Unlike alpha-amylase, glucoamylase adsorbed strongly onto raw starch, the adsorption site being non-identical with the active site.

Adsorption↗
PubMed1986

Secretion of alpha-amylase and multiple forms of glucoamylase by the yeast Trichosporon pullulans.

Trichosporon pullulans IGC 3488 produced extracellular alpha-amylase and glucoamylase activities when grown in batches in a medium containing corn steep liquor and soluble starch or corn starch. alpha-Amylase, unlike glucoamylase activity, was secreted biphasically. For both amylases the maximum concentration was found in stationary phase cultures. The amylolytic enzymes, previously concentrated by ammonium sulfate precipitation, were separated into a glucoamylase fraction and an alpha-amylase fraction by Ultrogel AcA 54 gel filtration. Pullulanase activity was located in the glucoamylase fraction, whereas cyclodextrinase activity was restricted to the alpha-amylase fraction. Isoamylase and alpha-glucosidase were not detected. Electrophoretic analysis showed that alpha-amylase activity was due to a single protein. Glucoamylase, however, occurred in multiple forms. The four glucoamylases and the alpha-amylase were glycoproteins.

Chromatography, Gel↗
PubMed1985

Purification and characterization of an extracellular glucoamylase from the yeast Candida tsukubaensis CBS 6389.

The starch-degrading yeast Candida tsukubaensis CBS 6389 secreted amylase at high activity when grown in a medium containing soluble starch. The extracellular alpha-amylase activity was very low. The major amylase component was purified by DEAE-Sephadex A-50 chromatography and Ultrogel AcA 44 gel filtration and characterized as a glucoamylase. The enzyme proved to be a glycoprotein with a molecular weight of 56 000. The glucoamylase had a temperature optimum at 55 degrees C and displayed highest activity in a pH range of 2.4-4.8. Acarbose strongly inhibited the purified glucoamylase. Debranching activity was present as demonstrated by the release of glucose from pullulan.

Candida↗
PubMed1985

Purification and Characterization of Extracellular Amylolytic Enzymes from the Yeast Filobasidium capsuligenum.

The extracellular amylolytic system of Filobasidium capsuligenum consisted of an alpha-amylase (1,4-alpha-d-glucan glucanhydrolase, EC 3.2.1.1) and two forms of glucoamylase (1,4-alpha-d-glucan glucohydrolase, EC 3.2.1.3). The enzymes were purified by ammonium sulfate fractionation, repeated ion-exchange chromatography (DEAE-Sephadex A-50), and gel filtration (Sephadex G-25, Sephadex G-100 sf). alpha-Amylase had an optimum pH of 5.6 and an optimum temperature of 50 degrees C but was rapidly inactivated at higher temperature. The molecular weight was estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be 64,000. An acarbose concentration of 20 mug/ml was required for 50% inhibition of the alpha-amylase. Both glucoamylases are glycoproteins of identical molecular weight (60,000) and produce only glucose by exohydrolysis. The debranching activity of the glucoamylases was evidenced with substrates containing alpha-1,6 linkages. The pH optima were 5.0 to 5.6 for glucoamylase I and 4.8 to 5.3 for glucoamylase II. Glucoamylase I had a higher optimum temperature (55 degrees C) than glucoamylase II (50 degrees C) and was also more resistant to thermal inactivation. Only low acarbose concentrations (<0.1 mug/ml) were required to reduce the activity of the glucoamylases by 50%.

Journal Article↗
PubMed1980

Identification of the quinone species in cyanide-sensitive and cyanide-insensitive mitochondria of Moniliella tomentosa.

Moniliella tomentosa was investigated for the presence of different quinones that might be involved in the cyanide-sensitive and/or cyanide-insensitive electron-transport pathways. The naturally occurring quinone in Moniliella tomentosa was found to be ubiquinone-45. Other quinone species could not be detected. The concentration of ubiquinone-45 in mitochondria is not related to the presence or absence of the alternative oxidase activity.

Chromatography, Thin Layer↗
PubMed1980

Stimulation of the alternative oxidase of Neurospora crassa by Nucleoside phosphates.

The alternative-oxidase-mediated succinate oxidase activity of Neurospora crassa decreases drastically when mitochondria are fractionated into submitochondrial particles or treated with deoxycholate. The activity, however, can be completely restored in the presence of nucleoside 5'-monophosphates. The purine nucleoside 5'-monophosphates are more effective than the pyrimidine homologues. 5'-GMP gives a 10-fold stimulation of the alternative-oxidase-mediated succinate oxidase activity in submitochondrial particles. A comparison is made with the results obtained earlier with Moniliella tomentosa [Hanssens & Verachtert (1976) J. Bacteriol. 125, 825--835; Vanderleyden, Van Den Eynde & Verachtert (1980) Biochem. J. 186, 309--316].

Deoxycholic Acid↗
PubMed1980

Substrate kinetics of the alternative oxidase of Neurospora crassa.

The kinetics of the succinate oxidation by cyanide-sensitive and cyanide-insensitive submitochondrial particles of Neurospora crassa cells suggest that both respiratory pathways use the same complex II. This is confirmed by comparing the kinetics of the reductase activities of the isolated succinate-ubiquinone oxidoreductase (complex II) of cyanide-sensitive and cyanide-insensitive cells respectively. No alternative-oxidase activity was found to be associated with the isolated complex II of cyanide-insensitive cells.

Chloramphenicol↗
PubMed1980

Nature of the effect of adenosine 5'-monophosphate on the cyanide-insensitive respiration in mitochondria of Moniliella tomentosa.

The alternative oxidase of Moniliella tomentosa mitochondria is stimulated by 5'-AMP. This effect may be masked, depending on the isolation procedure of the mitochondria. The preparation of submitochondrial particles results in the expression of the 5'-AMP effect. Two more methods are now described to reveal the 5'-AMP effect whenever it would be masked: (1) switching on the myokinase activity of the mitochondria to deplete them of endogenous 5'-AMP; (2) using detergents (sodium dodecyl sulphate, sodium deoxycholate) in a controlled detergent:protein ratio, or chloroform. The alternative oxidase of detergent-solubilized mitochondria was somewhat less selective towards nucleotides than were intact mitochondria. The effect of nucleotides on quinol oxidation by mitochondrial preparations and on quinol autoxidation was also studied. Mitochondrial oxidation of succinate by the alternative oxidase and autoxidation of quinols behaved similarly in the presence of certain nucleotides. Both reactions were stimulated. Both reactions were also inhibited by salicylhydroxamic acid. These effects on quinol oxidation disappeared when bovine serum albumin or mitochondrial proteins were present. From the results obtained it is not possible to exclude quinol autoxidation as a final step of the alternative oxidase.

Adenosine Monophosphate↗
PubMed1979

Characterization of cyanide-insensitive respiration in mitochondria and submitochondrial particles of Moniliella tomentosa.

Mitochondria and submitochondrial particles of the osmophilic yeast-like fungus Moniliella tomentosa may respire by means of two pathways: a normal cytochrome pathway, sensitive to cyanide and antimycin A, and an alternative pathway, which is insensitive to these inhibitors but is specifically inhibited by salicylhydroxamic acid. The affinities of both oxidases for succinate and NADH as substrates, for O(2) as terminal electron acceptor, and for AMP as stimulator of the alternative oxidase were determined. 1. Submitochondrial particles of M. tomentosa may also respire by means of a cyanide-sensitive and/or cyanide-insensitive system. 2. The activities of both oxidases as compared with the total activity are roughly the same in submitochondrial particles as in the original mitochondria. 3. The terminal oxidase of the cyanide-insensitive pathway requires a 10-fold higher O(2) concentration for saturation than does cytochrome c oxidase. 4. The apparent K(m) for succinate is about 3 times higher for the alternative than for the normal oxidase when measured in mitochondria, and 4-10 times higher when measured in submitochondrial particles. The apparent K(m) for NADH is roughly the same for both oxidases. 5. The apparent K(m) values of both oxidases for succinate are always lower in submitochondrial particles than in mitochondria. 6. The apparent K(m) for AMP, acting as a stimulator of the alternative oxidase, is the same (25mum) in mitochondria as in sub-mitochondrial particles. These results are discussed in the light of the structure and localization of the components of the alternative oxidase.

Adenosine Monophosphate↗
PubMed1978

[Disinfection of effluents from municipal sewage treatment plants with hydrogen peroxide (author's transl)].

Effluents from different sewage treatment plants were disinfected, using hydrogen peroxide in concentrations varying between 500 and 50,000 ppm. With a concentration of 5,500 ppm H2O2 and a contact time of 2 h more than 99% of bacteria were killed, including enterobacteria, total and fecal coliforms (Fig. 1 A, B, C and D) and fecal streptococci (Fig. 2 B). Staphylococci and micrococci were less sensitive and contact times of 2 h were not sufficient to kill 99% of this group (Fig. 2 A). Highly resistant were bacterial endospores (Fig. 2 C). With a concentration of 5% H2O2 50% of the spores still survived after a contact time of 2 h (Fig. 2 D). The effect of 5,500 ppm H2O2 by an exposure time of 2 h was then studied with other effluents. The results show that total counts were also reduced for 90% and some groups for more than 99% (table 1). There was no difference in reduction between catalase positive and catalase negative micro-organisms, indicating that the catalase activity of the bacteria offered no special resistance towards hydrogen peroxide in the concentrations used (table 2). Although the observations of some investigators have shown that metal ions act to increase the bactericidal effect of H2O2 as a result of formation of hydroxyl radicals, the additions of ferrous ions (5,25 and 50 ppm) did not improve the killing activity of H2O2 (table 3).

Disinfection↗
PubMed1978

Disinfection of effluents from municipal sewage treatment plants with peroxy acids.

Two peroxy acids, peracetic acid (PAA) and peroxy-monosulfuric acid or caro acid (CA) were tested as alternative bactericidal agents for the disinfection of effluents from municipal sewage treatment plants and their action was compared with chlorine. PAA added in a concentration of 2000 and 400 ppm, commonly used in medicin, killed in a few minutes 99.9% or more of most bacteria of the effluents (Fig. 1, A, B, C, D, E) excepted staphylococci and micrococci (Fig 1, F) and endospores (Fig. 1, G). These effects were comparable with those obtained with 5 ppm chlorine. Although these results indicate a very good killing effect, such concentrations of PAA are not applicable in practice, as they lowered the pH and increased the BOD of the effluent. When PAA was added in smaller amounts (10 and 5 ppm) no change of the pH and only a negligible increase of the BOD (Table 1) occured. These concentrations with a contact time of 15 min, gave a very good reduction of most bacterial groups, varying between 96% (total count, Fig. 1 A) and 100% (group-D streptococci, Fig. 1 E). With 1 ppm PAA the bactericidal action was slower, but after 30 minutes contact time the effects were similar to these of 5 ppm. It was also demonstrated that the effect of PAA was not affected by the number of bacteria in the effluent before treatment (Table 2), but well by the BOD. The addition of the inorganic CA in high concentrations had only a disadvantageous effect on the pH of the effluent, but no effect was noted when it was added in concentrations of 10 ppm. In this concentration, contact times of 120 min were necessary to kill about 90% of most bacteria (Fig. 2), showing that CA was only a weak disinfectant with slow action. It may be concluded that 5 ppm PAA could be a good alternative disinfectant for secondary effluents with a high degree of purification.

Disinfection↗
PubMed1976

Types of respiratory activity in Moniliella tomentosa during growth under different conditions.

The osmophilic yeastlike fungus Moniliella tomentosa is an obligate aerobe and is not susceptible to glucose repression. Respiration is greatest in exponentially growing cells and is then highly sensitive to cyanide. Respiration in older cells or in chloramphenicol-grown cells is mediated by a cyanide-insensitive respiration which is sensitive to salicyl hydroxamic acid. Growth of cells under reduced oxygen does not influence the respiratory capacity of the cells but results in a longer generation time and a lower final cell yield. Low aeration levels and growth in the presence of chloramphenicol have a profound effect on ethanol and polyol production.

Aerobiosis↗
PubMed1976

Adenosine 5'-monophosphate-stimulated cyanide-insensitive respiration in mitochondria of Moniliella tomentosa.

Mitochondria of the yeastlike fungus Moniliella tomentosa oxidize reduced nicotinamide adenine dinucleotide, reduced nicotinamide adenine dinucleotide phosphate, succinate, isocitrate, and lactate. These oxidations are completely inhibited by cyanide or antimycin A in mitochondria isolated from cells grown in the standard medium. On the other hand, the oxidation of all substrates, except lactate, is almost completely insensitive to cyanide or antimycin A in mitochondria from cells grown in the presence of ethidium bromide. In this instance, the oxidation is mainly mediated by an alternate oxidase which can be blocked by salicyl hydroxamic acid. The alternate oxidase can be specifically stimulated by adenosine 5'-monophosphate and this provides a new method for the characterization of the alternate oxidase in mitochondria of M. tomentosa.

Adenosine Diphosphate↗
PubMed1972

pH-dependent polyol production in Moniliella tomentosa.

Production of polyols by the yeastlike fungus Moniliella tomentosa could be increased by growing the organism at constant low pH. Up to 54% increase in yield was obtained. Growth at low pH also results in the production of D-arabitol which is not found in normal media.

Aerobiosis↗