PubMed Health⌕ Search

Biomedical subjects

D Visser

Publications and source records attributed to D Visser.

At least 19 recordsLinked to original sources
PubMed2001

Improved rapid sampling for in vivo kinetics of intracellular metabolites in Saccharomyces cerevisiae.

An integrated approach is used to develop a rapid sampling strategy for the quantitative analysis of in vivo kinetic behavior based on measured concentrations of intracellular metabolites in Saccharomyces cerevisiae. Emphasis is laid on small sample sizes during sampling and analysis. Subsecond residence times are accomplished by minimizing the dead volume of the sterile sampling system and by maximizing flow rates through application of vacuum to the sampling tubes in addition to the overpressure in the fermenter. A specially designed sample tube adapter facilitates sampling intervals of 4 to 5 s for various test tube types. Statistical analysis of the results obtained from enzymatic and liquid chromatography mass spectrometry (LC-MSMS) analysis of the metabolite concentrations was used to optimize the sampling protocol. The most notable improvement is reached through the introduction of vacuum drying of the cell extract. The presented system is capable of reliably dealing with fermenter samples as small as 1-g with a variation of less than 3%, and is thus ideally suited for intracellular measurements on small, lab-scale fermenters.

Biomass↗
PubMed2001

Polymerase chain reaction-restriction fragment-length polymorphism method to distinguish Liriomyza huidobrensis from L. Langei (Diptera: Agromyzidae) applied to three recent leafminer invasions.

A molecular method is presented for differentiating the morphologically cryptic leafminers Liriomyza langei Frick and L. huidobrensis (Blanchard). This method requires polymerase chain reaction (PCR) amplification of a 1031-bp region of mitochondrial cytochrome oxidase DNA followed by restriction fragment analysis using the restriction enzymes SpeI and EcoRV. Spel cuts the mitochondrial fragment of L. langei into two fragments, but does not cut the L. huidobrensis fragment. EcoRV cuts the L. huidobrensis fragment into two fragments, but does not cut the L. langei fragment. This PCR-restriction fragment-length polymorphism (RFLP) method is faster and less costly than DNA sequencing,which is currently the only other way to differentiate these two species. We apply the method to samples from recently introduced leafminer populations in Sri Lanka, Canada, and South Africa and find that the invasive leafminer in all three locations is L. huidobrensis.

Animals↗
PubMed2000

Glucose and the ATP paradox in yeast.

A sustained decrease in the intracellular ATP concentration has been observed when extra glucose was added to yeast cells growing aerobically under glucose limitation. Because glucose degradation is the main source of ATP-derived free energy, this is a counter-intuitive phenomenon, which cannot be attributed to transient ATP consumption in the initial steps of glycolysis. We present a core model for aerobic growth in which glucose supplies carbon, as well as free energy, for biosynthesis. With Metabolic Control Analysis and numerical simulations, we demonstrate that the decrease in the ATP concentration can be reproduced if the biosynthetic route is more strongly activated by carbon substrates than is the catabolic (ATP-producing) route.

Adenosine Triphosphate↗
PubMed2000

Chiral critical exponents of the triangular-lattice antiferromagnet CsMnBr3 as determined by polarized neutron scattering

The critical exponents gamma(c) = 0.84(7) of the chiral susceptibility above the Neel temperature, T(N), and beta(c) = 0. 44(2) of the average chirality below T(N) have been determined for the triangular-lattice antiferromagnet CsMnBr3 by means of polarized neutron scattering. These first experimental values of chiral critical exponents are in line with theoretical predictions and fulfill their scaling relation. The temperature at which the average chirality appears coincides with the spin-order transition temperature, T(N).

Journal Article↗
PubMed2000

Tendency modeling: a new approach to obtain simplified kinetic models of metabolism applied to Saccharomyces cerevisiae.

A novel approach to construct kinetic models of metabolic pathways, to be used in metabolic engineering, is presented: the tendency modeling approach. This approach greatly facilitates the construction of these models and can easily be applied to complex metabolic networks. The resulting models contain a minimal number of parameters; identification of their values is straightforward. Use of in vitro obtained information in the identification of the kinetic equations is minimized. The tendency modeling approach has been used to derive a dynamic model of primary metabolism for aerobic growth of Saccharomyces cerevisiae on glucose, in which compartmentation is included. Simulation results obtained with the derived model are satisfying for most of the carbon metabolites that have been measured. Compared to a more detailed model, the simulations of our model are less accurate, but taking into account the much smaller number of kinetic parameters (35 instead of 84), the tendency the modeling approach is considered promising.

Biomedical Engineering↗
PubMed1998

Fungal bezoars as a cause of renal insufficiency in neonates and infants--recommended treatment strategy.

Fungal bezoars may be a cause of urinary tract obstruction and acute renal failure in neonates and young infants. We describe a female very low birth weight infant (25+3 weeks, 795 gram) who developed renal insufficiency on the basis of systemic fungal infection with fungal bezoars in both kidneys. The girl was treated by local irrigation of the kidneys and bladder with amphotericin B via percutaneously inserted bilateral nephrostomy catheters, in combination with intravenous fluconazol. Renal function subsequently improved and after 11 weeks of treatment the bezoars had disappeared sonographically. Follow-up of this child and the one we similarly treated for fungal bezoars before, however, shows suboptimal renal function as assessed by the clearance of creatinine and the mercapto acetyl triglycine scan (MAG III). Until now, insufficient data are available yet to assess with certainly the long-term effects of fungal bezoars on renal function. Based on our experience and a review of the recent literature (1980-1996) on systemic candidal infections in premature infants, we recommend to perform regular renal ultrasound in any case of systemic candidal infection in a prematurely born infant. If candidal bezoars are found with pelvic obstruction, we suggest to start treatment by the insertion of bilateral nephrostomy catheters and local irrigation with amphotericin B in combination with systemic antifungal agents, aiming at both the restoration of renal function and the eradication of the fungal infection.

Candidiasis↗
PubMed1992

[Nutrition pumps in pediatrics: a comparative study].

Home enteral nutrition as the sole or as an additional way of feeding children is becoming increasingly popular. It can be used in the form of bolus-feeding, or as drip-feeding, either continuous (24 hours) or semicontinuous (nightly). For the latter method usually a feeding pump is used. In the Netherlands several feeding pumps are available, which were tested in this report. These feeding pumps (Compat, Enteroport, Flexiflo Companion, Flocare 500, Frenta Mat, Frenta-System II, Kangaroo 324, Nutromat Päd S, Nutromat S) were investigated for accuracy, available rate-settings, adequate alarming at interruption of the drip feeding, weight and ease of operation. All pumps were tested stationary, and suitable pumps weighing less than 1000 grams were subsequently tested ambulatory. The nine tested pumps were all fairly easy to operate. Three pumps were not suitable for pediatric use, either because the infusion rate was more than 30% out of range (Flexiflo Companion) or because of inadequate rate settings (Nutromat S and Frentasystem II; respectively 20 and 25 ml/hour minimally). Accuracy for the other pumps was always within 10% of the set rate. One pump, the Enteroport, has a rate setting which is suboptimal for pediatric use. In addition this pump does not alarm when the drip feeding is interrupted. The other pumps (Compat, Frenta Mat, Kangaroo 324, Flocare 500, and Nutramat Päd S) are all suitable for pediatric use, both with respect to the rate settings as to the adequate alarming when the drip feeding is interrupted. The Flocare 500 and the Nutromat Päd S, in addition to the Enteroport, have a weight below 1000 grams.(ABSTRACT TRUNCATED AT 250 WORDS)

Consumer Product Safety↗