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B Völker

Publications and source records attributed to B Völker.

At least 19 recordsLinked to original sources
PubMed1997

Different activation energies in glucose uptake in Saccharomyces cerevisiae DFY1 suggest two transport systems.

The analysis of initial glucose uptake in Saccharomyces cerevisiae at 25 degrees, 20 degrees, 15 degrees and 10 degrees C by computer-assisted nonlinear regression analysis predicts two transport systems. The first demonstrates Michaelis-Menten kinetics and the second shows first order behaviour. The activation energies of these two systems were calculated by the Arrhenius equation at four different growth phases, namely early exponential (EE), middle exponential (ME2), late exponential (LE) and early stationary (ES) with 2% glucose in the batch medium. The activation energies calculated from the V(m) values in EE, ME, LE and ES growth phases were 15.8 +/- 1.7, 13.5 +/- 1.0, 15.1 +/- 0.8 and 13.5 +/- 0.7 kcal/mol. These values are in agreement with activation energies calculated for the first mechanism, facilitated diffusion, which is the mechanism deduced from countertransport experiments. The activation energies derived for the second transport system from the first order rate constants in cells grown to EE, ME2, LE and ES were 8.0 +/- 2.1, 8.1 +/- 1.3, 9.6 +/- 3.0 and 7.5 +/- 2.6 kcal/mol. These values are still significantly higher than for free diffusion of glucose in water and lower as predicted for passage of glucose through the lipid phase. Therefore, we assume in addition to carrier-mediated facilitated diffusion the entrance of glucose into the cell through a pore.

Biological Transport↗
PubMed1993

Misuse of graphical analysis in nonlinear sugar transport kinetics by Eadie-Hofstee plots.

It has become common practice to analyse the sugar transport kinetics from initial uptake rates in Saccharomyces cerevisiae cells with Eadie-Hofstee plots. These plots often demonstrate a nonlinear behaviour. They have been resolved incorrectly into two quasilinear components indicating the presence of (at least) two uptake systems or components, with Km values differing by a factor of about 10. This graphical analysis neglects the obvious additivity of the two hypothetical systems and is therefore in error. A more efficient way to determine kinetic parameters from initial uptake experiments is to use computer-assisted nonlinear regression analysis.

Glucose↗
PubMed1992

Mast cell frequency in soft tissue tumors. Relation to type and grade of malignancy.

A high content of mast cells (MC) is considered characteristic of neurofibromas but not of malignant schwannomas and neurilemmomas. We examined the extent and reliability of this finding by counting MC in 61 peripheral nerve sheath tumors and in 103 non-neurogenic soft tissue sarcomas. We furthermore investigated correlations between the amount of MC and various features of the tumors (e.g. grades of malignancy). Neurofibromas had very high mast cell counts. However, this result only applied to about 70% of these tumors. Malignant schwannomas, malignant fibrous histiocytomas and leiomyosarcomas had remarkably high median values of MC counts with a wide dispersion within the histological groups. Synovial sarcomas were the only group that contained MC in every case, though often in small numbers. In univariate analyses the number of MC was negatively correlated to grades of malignancy, cellularity and mitotic activity of the sarcomas and tended to correlate positively to the amount of myxoid and collagenous connective tissue and lymphocytic infiltrates. Multiple linear regression analysis revealed a significant correlation to the grade of malignancy and the amount of connective tissue.

Cell Count↗
PubMed1991

[Zygomycoses: clinical aspects and pathology in 10 patients].

Deep fungal infections caused by zygomycetes (so-called mucormycoses) are rare. Whereas in the past rhinocerebral mycosis dominated, today a wide range of clinical manifestations must be expected, especially pulmonary infections and invasion of vessel walls with systemic infarction. On the basis of 10 cases of Mucoraceae mycosis and a review of the literature, the predisposing conditions, clinical symptoms and pathologic-anatomic findings are described. Our observations include 7 patients with leukemia and 2 adults and one newborn without malignant neoplasia. Except for the patient with rhinocerebral mycosis, the diagnosis was not established during the patients' lifetime. 3 patients received systemic antimycotic therapy. Our observations suggest that infarctions of internal organs in immunocompromised patients should direct suspicion towards angio-related mycoses, not only of aspergillosis, but also of zygomycosis.

Adult↗
PubMed1989

Kinetic analysis and simulation of glucose transport in plasma membrane vesicles of glucose-repressed and derepressed Saccharomyces cerevisiae cells.

In this study experimental data on the kinetic parameters investigated by other authors 1-5, 11 together with own data on plasma membrane vesicles, have been subjected to a computer simulation based on the equations describing facilitated diffusion. The simulation led to an ideal fit describing the above data. From this it can be concluded that glucose is transported by facilitated diffusion, and not by active transport as was postulated by Van Steveninck 14,15. The simulation method also demonstrates that the fast sampling technique used by these authors 1-5, 11 underestimated the fluxes. Thus, the parameters given do not contribute to the understand of glucose transport under different metabolic conditions. The K value of plasma membrane vesicles prepared from glucose-repressed cells is around 7 mM. Derepression, particularly by galactose, causes a highly significant increase in affinity as shown by a decrease in the K value to 2 mM. The highest affinity was measured in a triple kinaseless mutant grown on glycerol with a K value of 1 mM. It seems, therefore, that the kinetic parameters derived from initial uptake rates of glucose in intact cells 1-5, 11 using single flux analysis, such as Eadie-Hofstee- or Lineweaver-Burk-plots, are in error.

Biological Transport↗
PubMed1989

Lyme-borreliosis and possible association with HLA-antigens.

The frequencies of HLA A, B, C and DR antigens were evaluated in 220 persons from West Germany with inapparent and manifest Borrelia burgdorferi infections. Thirty-seven forest workers showing elevated antibody titres against Borrelia burgdorferi had asymptomatic infection, and are described as stage 0. One hundred and eighty-three patients presented with the clinical stages 1-3 of the infection. Control persons (n = 655) were typed in the same time period and by identical staff. HLA CW3 was present in 36.3% of patients as compared to 23.2% of the controls (RR = 1.88, pcorr = 0.03) and was significantly associated with manifest infection. In addition, the antigen A2 was found slightly but not significantly more frequent in the patients (55.2% vs 44%; pcorr = 0.41). The phenotype combination HLA A2 and Cw3, however, was significantly elevated in patients (24.6% vs 10.8%; pcorr = 0.0005). In contrast to these class 1 antigens, HLA DR3 showed a tendency of negative association with manifest infection. But this finding was not yet found to be significant (15.3% vs 25.3%; RR = 0.53, pcorr = 0.26). The frequency of HLA DR2 showed a constant decrease from stage 0 to stage 3 (inapparent infection to late complications). Using the rank correlation coefficient of Spearman, this association was found to be significant (-1.00, p less than or equal to 0.05). All other tested HLA antigens and antigen combinations showed no significant differences. The data suggest that HLA CW3 may be associated with Borrelia burgdorferi infection, whereas HLA DR2 and DR3 may be associated with less incidence of severe courses and less complications in this disorder.

Borrelia Infections↗
PubMed1987

[Glaucoma].

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Glaucoma↗
PubMed1987

[Strabismus].

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Humans↗
PubMed1986

A comparison of the influence of temporary balloon buckles and permanent episcleral silicone sponges on postoperative ocular motility in retinal detachment surgery.

The influence of retinal surgery on ocular motility was examined in 60 patients with rhegmatogenous retinal detachment caused by one tear. Thirty patients were treated with cryotherapy and an episcleral radial silicone sponge explant. The remaining 30 patients were treated with a Lincoff temporary balloon buckle procedure. Extensive pre- and postoperative orthoptic examinations showed the impairment of ocular motility to be significantly less with the balloon-buckle procedure.

Eye↗