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W A Scheffers

Publications and source records attributed to W A Scheffers.

52 records · Page 3Linked to original sources
PubMed1983

An enzymic analysis of NADPH production and consumption in Candida utilis.

Candida utilis CBS 621 was grown in chemostat cultures at D = 0.1 h-1 on glucose, xylose, gluconate, acetate, or ethanol as the growth-limiting substrate with ammonia or nitrate as the nitrogen source and analysed for NADPH-producing and NADPH-consuming enzyme activities. Nitrate and nitrite reductases were strictly NADPH-dependent. For all carbon sources, growth with nitrate resulted in elevated levels of HMP pathway enzymes. NADP+-linked isocitrate dehydrogenase did not vary significantly with the NADPH requirement for biosynthesis. Growth on ethanol strongly enhanced activity of NADP+-linked aldehyde dehydrogenase. Neither NADP+-linked malic enzyme nor transhydrogenase activities were detectable under any of the growth conditions. The absence of transhydrogenase was confirmed by the enzyme profiles of cells grown on mixtures of glucose and formate. It is concluded that the HMP pathway and possibly NADP+-linked isocitrate dehydrogenase are the major sources of NADPH in Candida utilis.

Candida↗
PubMed1981

Metabolism of acetaldehyde and custers effect in the yeast.

Brettanomyces abstinens growing on different initial glucose concentrations showed an anaerobic inhibition of fermentation. This Custers effect decreased as the initial glucose concentration in the medium increased. Two aldehyde dehydrogenases, one NAD+-linked and the other NADP+-linked were observed. The results suggest that the NAD+-linked enzyme is involved in the production of acetic acid and is repressed by glucose. The NADP+-linked enzyme seems to be a constitutive enzyme. Acetyl-CoA synthetase activity also was not greatly affected by the growth conditions. The results support the earlier hypothesis that the Clusters effect in Brettanomyces is provoked by the reduction of NAD+ in the conversion of acetaldehyde to acetic acid.

Acetaldehyde↗
PubMed1980

False-negative oxidase reaction as a result of medium acidification.

Acidification of the culture medium may lead to a false-negative result of the oxidase reaction. Hence, if the medium contained a carbon source or another component that is convertible to acid, a negative oxidase reaction should be considered inconclusive. In order to eliminate false-negative reactions, a reagent freshly adjusted to pH 5-7 might be used; this reagent should be checked on known oxidase-negative strains. However, we recommend that the oxidase test be performed with the normal reagent after (sub)culturing on a non-acidogenic medium.

Aeromonas↗
PubMed1975

Effects of some chemical factors on flagellation and swarming of Vibrio alginolyticus.

Vibrio alginolyticus strains recently isolated from Dutch coastal seawater changed flagellar organization when cultivated in the presence of certain chemical agents. On agar media with more than 4.0% (w/v) NaCl the number of lateral flagella per cell decreased with increasing salt concentration. Both on agar media and in broth cultures with 6.0-9.0% (w/v) NaCl, cells with polar tufts of 2-4 sheathed or unsheathed flagella were frequently found. Cells grown on agar media with 7.3-9.8% (w/v) Na2SO4 had drastically reduced numbers of lateral flagella, but lacked polar tufts. EDTA suppressed growth, but did not affect flagellar arrangement. In the presence of 0.1-0.3% boric acid or 0.05-0.1% aluminum hydroxide, cells in liquid media tended to produce lateral, in addition to the polar flagella normally observed in broth cultures. Of a number of surface-active agents tested, Tween 80 and Na-taurocholate, even in high concentrations, did not affect flagellation. Bile salts (0.1%) and Na deoxycholate (0.05%) strongly reduced the number of both polar and lateral flagella. In agar cultures, Na-lauryl sulphate (0.01-0.1%) inhibited the formation of lateral, but increased the incidence of polar flagella. Teepol (0.05-0.2%) had a similar effect and also it had a deteriorating effect on the sheaths of the polar flagella. Concomitant with the reduction in the number of lateral flagella, induced by these agents, swarming on agar media was inhibited.

Agar↗
PubMedDate not supplied

Kinetics of growth and glucose transport in glucose-limited chemostat cultures of Saccharomyces cerevisiae CBS 8066.

The glucose transport capacity of Saccharomyces cerevisiae CBS 8066 was studied in aerobic glucose-limited chemostat cultures. Two different transport systems were encountered with affinity constants of 1 and 20 mM, respectively. The capacity of these carriers (Vmax) was dependent on the dilution rate and the residual glucose concentration in the culture. From the residual glucose concentration in the fermenter and the kinetic constants of glucose transport, their in situ contribution to glucose consumption was determined. The sum of these calculated in situ transport rates correlated well with the observed rate of glucose consumption of the culture. The growth kinetics of S. cerevisiae CBS 8066 in glucose-limited cultures were rather peculiar. At low dilution rates, at which glucose was completely respired, the glucose concentration in the fermenter was constant at 110 microM, independent of the glucose concentration in the reservoir. At higher dilution rates, characterized by the occurrence of both respiration and alcoholic fermentation, the residual substrate concentration followed Monod kinetics. In this case, however, the overall affinity constant was dependent on the reservoir glucose concentration.

Biological Transport↗
PubMedDate not supplied

Substrate-accelerated death of Saccharomyces cerevisiae CBS 8066 under maltose stress.

When Saccharomyces cerevisiae CBS 8066 was grown under maltose limitation, two enzymes specific for maltose utilization were present: a maltose carrier, and the maltose-hydrolysing alpha-glucosidase. The role of these two enzymes in the physiology of S. cerevisiae was investigated in a comparative study in which Candida utilis CBS 621 was used as a reference organism. Maltose pulses to a maltose-limited chemostat culture of S. cerevisiae resulted in 'substrate-accelerated death'. This was evident from: (1) enhanced protein release from cells; (2) excretion of glucose into the medium; (3) decreased viability. These effects wee specific with respect to both substrate and organism: pulses of glucose to maltose-limited cultures of S. cerevisiae did not result in cell death, neither did maltose pulses to maltose-limited cultures of C. utilis. The maltose-accelerated death of s. cerevisiae is most likely explained in terms of an uncontrolled uptake of maltose into the cell, resulting in an osmotic burst. Our results also provide evidence that the aerobic alcoholic fermentation that occurs after pulsing sugars to sugar-limited cultures of s. cerevisiae (short-term Crabtree effect) cannot solely be explained in terms of the mechanism of sugar transport. Both glucose and maltose pulses to maltose-limited cultures triggered aerobic alcohol formation. However, glucose transport by S. cerevisiae occurs via facilitated diffusion, whereas maltose entry into this yeast is mediated by a maltose/proton symport system.

Carrier Proteins↗
PubMedDate not supplied

Determination of protein concentration by total organic carbon analysis.

Determination of the carbon concentration in protein solutions by total organic carbon analysis was found to be a sensitive and reliable method for the estimation of protein concentrations. Using a carbon content of 0.53 g/g in protein and of 0.44 g/g in carbohydrate, the concentrations of normal proteins, proteins containing chromophoric groups, and proteins containing carbohydrate could be established. The method appeared to be independent of the nature of the protein and showed complete linearity between 25 and 1000 mg/l (0.5-20 micrograms per assay) when protein was serially diluted. Determination of specific absorption coefficients by measuring both the absorbance of protein solutions at 280 nm and their carbon concentrations gave values which, on the average, coincided within 12% with values reported in the literature. The method may have special applicability in protein purification studies, as it does not require knowledge of molar extinction coefficients beforehand, and also monitors the disappearance of carbon compounds other than protein.

Carbon↗