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N Van Uden

Publications and source records attributed to N Van Uden.

17 recordsLinked to original sources
PubMed2000

Rabaptin4, a novel effector of the small GTPase rab4a, is recruited to perinuclear recycling vesicles.

The small GTPase rab4a is associated with early endocytic compartments and regulates receptor recycling from early endosomes. To understand how rab4a mediates its function, we searched for proteins which associate with this GTPase and regulate its activity in endocytic transport. Here we identified rabaptin4, a novel effector molecule of rab4a. Rabaptin4 is homologous with rabaptin5 and contains a C-terminal deletion with respect to rabaptin5. Rabaptin4 preferentially interacts with rab4a-GTP and to a lesser extent with rab5aGTP. We identified a rab4a-binding domain in the N-terminal region of rabaptin4, and two binding sites for rab5, including a novel N-terminal rab5a-binding site. Rabaptin4 is a cytosolic protein that inhibits the intrinsic GTP hydrolysis rate of rab4a and is recruited by rab4a-GTP to recycling endosomes enriched in cellubrevin and internalized indocarbocyanine-3 (Cy3)-labelled transferrin. We propose that rabaptin4 assists in the docking of transport vesicles en route from early endosomes to recycling endosomes.

Amino Acid Sequence↗
PubMed1990

Inverse Diauxy in the Yeast Hansenula anomala: Mutants Derepressed for Malic Acid Utilization in the Presence of Glucose.

Utilization of l-malic acid by yeast strain Hansenula anomala IGC 4380 is subject to glucose repression. Derepressed mutants were obtained with UV light by use of the nonmetabolizable glucose analog 2-deoxyglucose as a selective agent. Three mutant strains degraded l-malic acid in the presence of up to 30% (wt/vol) glucose and are of potential interest for the biological deacidification of grape must. The mutant strains, as compared with the parent strain, displayed inverse diauxy in glucose-malate medium, glucose being metabolized only after malate consumption had been completed.

Journal Article↗
PubMed1989

Leucosporidium fellii sp. nov., a basidiomycetous yeast that degrades L(+)-tartaric acid.

A new species of basidiomycetous yeast Leucosporidium fellii was isolated from soil in Portugal on a selective L(+)-tartaric acid medium. This yeast is self-sporulating but forms dikaryotic hyphae with clamp connections and is presumably homothallic. It differs from the type strain of Leucosporidium scottii in its life cycle, assimilation pattern and guanine-cytosine content and from the other described Leucosporidium species by additional characteristics.

Basidiomycota↗
PubMed1987

Role of de novo protein synthesis in the interconversion of glucose transport systems in the yeast Pichia ohmeri.

Glucose-repressed cells of the yeast Pichia ohmeri IGC 2879 transported glucose by facilitated diffusion. Derepression led to the formation of a glucose/proton symport and the simultaneous reduction of the facilitated diffusion capacity by about 70%. Cycloheximide prevented this interconversion indicating its dependence on de novo protein synthesis (proteosynthetic interconversion). In buffer with 2% glucose the glucose/proton symport suffered irreversible inactivation while the facilitated diffusion system was simultaneously restored. This reverse interconversion process did not require de novo protein synthesis as indicated by its lack of sensitivity to cycloheximide (degradative interconversion). Thus the glucose/proton symport system appeared to consist of about 70% of the facilitated diffusion proteins turned silent through association with additional protein(s) the latter being sensitive to glucose-induced repression and glucose-induced inactivation.

3-O-Methylglucose↗
PubMed1985

The temperature profiles of growth, thermal death and ethanol tolerance of the xylose-fermenting yeast Candida shehatae.

The temperature profile of growth and thermal death of the xylose-fermenting yeast Candida shehatae was dissociative. The ARRHENIUS plot of growth lacked a descending supraoptimal branch and the specific growth rate at the maximum temperature for growth (around 31 degrees C) was not significantly different from its values at the other temperatures studied (down to 20 degrees C). Ethanol enhanced thermal death by increasing its entropy of activation (entropy coefficient 16.1 entropy units mol-1]-1). The temperature profile of ethanol tolerance with respect to growth displayed a temperature plateau (10-17.5 degrees C) of maximum ethanol tolerance (limit 6% v/v of ethanol) while the toxic effects of ethanol increased on either side of the plateau depressing the maximum temperature for growth from 31 to 17.5 degrees C and increasing the minimum temperature for growth from 2.5 to 10 degrees C.

Candida↗
PubMed1984

Effects of ethanol and other alkanols on passive proton influx in the yeast Saccharomyces cerevisiae.

Ethanol, isopropanol, propanol and butanol enhanced the passive influx of protons into deenergized cells of Saccharomyces cerevisiae. The influx followed first-order kinetics with a rate constant that increased exponentially with the alkanol concentration. The exponential enhancement constants increased with the lipid solubility of the alkanols, which indicated hydrophobic membrane regions as the target sites. While the enhancement constants were independent of pH over the range tested (3.3-5.0), the rate constants decreased linearly with increasing extracellular proton concentration, indicating the presence of an additional surface barrier against proton penetration, the effectiveness of which increased with protonation. The alkanols affected the acidification curves of energized yeast suspensions in such a way that the final pH values were linear functions of the alkanol concentrations. These results were consistent with a balance between active and passive proton movements at the final pH, the exponential enhancement constants calculated from the slopes being nearly identical with those obtained with deenergized cells. It was concluded that passive proton influx contributes to the kinetics of acidification in S. cerevisiae and that uncoupling contributes to the overall kinetics of alkanol-inhibited secondary active transport across the yeast plasma membrane.

Acid-Base Equilibrium↗
PubMed1983

Effects of cycloheximide on the temperature profile of Sacharomyces cerevisiae.

Tmax, the maximum temperature for growth of Saccharomyces cerevisiae, decreased linearly with increasing concentrations of cycloheximide added to the medium, to about 20 degrees C at 2.5 microgram ml-1. In this concentration range thermal death was not enhanced. The Arrhenius plot of growth was shifted to lower temperatures as a function of the cycloheximide concentration and became dissociated from the Arrhenius plot of thermal death. It was concluded that the target site of cycloheximide, the cytoplasmic ribosome, is not identical with the physiological Tmax site of S. cerevisiae and that the binding of cycloheximide to its target sites is strongly enhanced by the temperature.

Cycloheximide↗
PubMed1982

The temperature profile of growth, death and yield of the starch-converting yeast Lipomyces kononenkoae.

A strain of Lipomyces kononenkoae earlier proposed for industrial starch bioconversion was found to have a dissociative temperature profile. The Arrhenius plot of sustained exponential growth displayed a single branch between the optimum (32-33 degrees C) and the maximum (about 35 degrees C) temperature for growth while the extrapolated Arrhenius plots of growth and thermal death intersected at a biologically non-significant value. The yield of L. kononenkoae on glucose did not decrease at supraoptimal temperatures while the associative yeast Saccharomyces cerevisiae suffered yield decreases above the optimum temperature for growth with increasing temperature.

Ascomycota↗
PubMed1982

The temperature profile of the pathogenic yeast Candida albicans.

A strain of Candida albicans was found to have an associative temperature profile with respect to growth, thermal death and yield on glucose. The ARRHENIUS plot of sustained exponential growth displayed two branches in the supraoptimal temperature range with the optimum temperature for growth around 33 degrees C, the final maximum temperature for growth around 38 degrees C and the initial maximum temperature for growth around 42 degrees C. The yield on glucose was temperature dependent in the supraoptimal range and declined linearly to zero between the optimum and the initial maximum temperature for growth.

Candida albicans↗
PubMed1977

Isothermic variation of the specific growth rate of Saccharomyces cerevisiae in batch culture.

The specific growth rate (mu) of a respiration-deficient mutant of Saccharomyces cerevisiae growing under defined experimental conditions in batch culture (mineral medium plus glucose and vitamins at 25 degrees C) varied from experiment to experiment over a wide range (0.10-0.24 h-1) and showed a normal distribution. Neither the age of the culture, the history of the inoculum, nor experimental error accounted wholly for the variability of mu. The variation was positively correlated with the specific rate of glucose transfer and negatively with the specific rate of production of non-fermentative CO2. The yield decreased with mu implying higher maintenance requirements in batch culture (4.7 mmoles g-1 h-1) than in continuous culture (0.8 mmoles g-1 h-1). It was concluded that the strain is capable of establishing any one of several steady states of growth under the same experimental conditions, each steady state displaying some build in inertia with respect to change. The variations of the specific rates of glucose transfer and non-fermentative CO2 production, and of the yield appeared to be consequences rather than causes of the variation of mu. The ultimate causes of the variation of mu remained unidentified.

Carbon Dioxide↗
PubMed1976

Yield and maintenance relations of yeast growth in the chemostat at superoptimal temperatures.

A model is proposed that accounts for the decreases in yield which occur in chemostat cultures of mesophilic yeasts at superoptimal growth temperatures. Two yield depressing effects were identified, one due to increased maintenance requirements by the viable fraction of the population, the other due to energy substrate dissipation by the nonviable function. The two effects are functions of the dilution rate, as is the fraction of nonviable cells. Experimental results were obtained on the yield, maintenance, and dissipation of energy substrate in a glucose-limited chemostat culture of a respiration-deficient mutant of Saccharomyces cerevisiae at 39 degrees C. The rates of glucose utilization for maintenance and for dissipation constituted, respectively, 33-28% and 15-9% of the total glucose utilization rate over the range of dilution rates tested (0.038-0.064 hr-1), while the yield varied over this range from 0.066-0.085 g of biomass (dry wt) per gram of glucose.

Glucose↗
PubMed1976

Thermodynamic conpensation in microbial thermal death. Studies with yeasts.

Sixty eight Arrhenius plots of thermal death in six mesophilic yeast species, tested at various concentrations of NaC1, lacked an isokinetic temperature. Nevertheless the deltaHnot equal to/deltaSnot equal to plot was apparently linear with a slope corresponding to 314degrees K. It was concluded the linear thermodynamic compensation of thermal death is non-existent in heterogeneous groups of yeasts and is unlikely to occur in hetero-geneous groups of other organisms and that deltaHnot equal to/deltaSnot equal to plots lack sensitivity for the detection of non-linearity over narrow temperature ranges. However, the deltaHnot equal to and deltaSnot equal to parameters of thermal death displayed non-linear compensation in such a way that the extrapolated Arrhenius plots of death attained nearly identical values near the respective maximum temperatures for growth. Linear thermodynamic compensation occurred in each of the six strains, when stationary populations of the same strain were tested at various NaC1 concentrations. On the other hand, exponential populations of each of the strains, tested in the same way, lacked an isokinetic temperature of thermal death. The significance of linear and non-linear thermodynamic compensation in biological rate processes is discussed.

Cell Survival↗
PubMed1975

Dependence of the maximum temperature for growth of Saccharomyces cerevisiae on nutrient concentration.

Saccharomyces cerevisae was grown in a chemostat under glucose limitation at three superoptimal temperatures. In each steady state the specific growth rate was the sum of the dilution rate and the specific death rate, exponential death occurring with exponential growth. The specific death rate was a function of both the temperature and the concentration of the limiting nutrient. Each superoptimal temperature was characterized by a critical glucose concentration below which net growth was not possible. The critical glucose concentration increased with the temperature. Consequently the maximum temperature for growth was a function of the concentration of the limiting nutrient and approached the optimum temperature for growth with decreasing glucose concentrations.

Cell Count↗