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Biomedical subjects

K Menzel

Publications and source records attributed to K Menzel.

At least 19 recordsLinked to original sources
PubMed2003

Crossover behavior in micellar solutions with lower critical demixing point: broadband ultrasonic spectrometry of the isobutoxyethanol-water system.

The aggregation kinetics of isobutoxyethanol-water mixtures with lower critical demixing point has been investigated. Two types of kinetics have been observed, a diffusion-controlled formation of micellar species and the formation of a microheterogeneous liquid structure, governed by fluctuations in the local concentration. Ultrasonic attenuation spectra of isobutoxyethanol-water mixtures have been measured between 100 kHz and 2 GHz at 25 degrees C and at several concentrations, covering the complete composition range. With the mixture of critical composition measurements have been performed at some temperatures near the critical temperature (T(c)=299.51 K). In addition to the asymptotic high frequency background contribution, the broadband spectra reveal a Bhattacharjee-Ferrell relaxation term due to critical concentration fluctuations, a restricted Hill term reflecting the monomer exchange between micelles and the suspending phase, and two Debye-type relaxation terms that are assigned to chemical relaxations. The relaxation rates of the Bhattacharjee-Ferrell term exceed those from static and dynamic light scattering (amplitude Gamma(0)=5.3 x 10(9) s(-1)), likely due to the effect of a second parallel pathway of relaxation in the ultrasonic field. The adiabatic coupling constant following from the amplitude in the ultrasonic spectrum agrees with that from a thermodynamic relation (g=1.3). The restricted Hill term displays the features of an extended Teubner-Kahlweit-Aniansson-Wall model of the micelle formation and decay kinetics in surfactant solutions with high critical micelle concentration (C=0.6 mol/l). The idea of a fluctuation controlled monomer exchange in aqueous solutions of poly(ethylene glycol) monoalkyl ether-water mixtures near the critical point is briefly discussed.

Journal Article↗
PubMed1999

Microbial production of 1,3-propanediol.

1,3-Propanediol (1,3-PD) production by fermentation of glycerol was described in 1881 but little attention was paid to this microbial route for over a century. Glycerol conversion to 1,3-PD can be carried out by Clostridia as well as Enterobacteriaceae. The main intermediate of the oxidative pathway is pyruvate, the further utilization of which produces CO2, H2, acetate, butyrate, ethanol, butanol and 2,3-butanediol. In addition, lactate and succinate are generated. The yield of 1,3-PD per glycerol is determined by the availability of NADH2, which is mainly affected by the product distribution (of the oxidative pathway) and depends first of all on the microorganism used but also on the process conditions (type of fermentation, substrate excess, various inhibitions). In the past decade, research to produce 1,3-PD microbially was considerably expanded as the diol can be used for various polycondensates. In particular, polyesters with useful properties can be manufactured. A prerequisite for making a "green" polyester is a most cost-effective production of 1,3-PD, which, in practical terms, can only be achieved by using an alternative substrate, such as glucose instead of glycerol. Therefore, great efforts are now being made to combine the pathway from glucose to glycerol successfully with the bacterial route from glycerol to 1,3-PD. Thus, 1,3-PD may become the first bulk chemical produced by a genetically engineered microorganism.

Adenosine Triphosphate↗
PubMed1998

Kinetic, dynamic, and pathway studies of glycerol metabolism by Klebsiella pneumoniae in anaerobic continuous culture: IV. Enzymes and fluxes of pyruvate metabolism.

The activities of pyruvate kinase (PK), pyruvate: formate-lyase (PFL), pyruvate dehydrogenase (PDH), and citrate synthase (CS) involved in the anaerobic glycerol conversion by Klebsiella pneumoniae were studied in continuous culture under conditions of steady states and sustained oscillations. Both the in vitro and in vivo activities of PK, PFL, and PDH are strongly affected by the substrate concentration and its uptake rate, as is the in vitro activity of CS. The flux from phosphoenolpyruvate to pyruvate is found to be mainly regulated on a genetic level by the synthesis rate of PK, particularly at low substrate concentration and low growth rate. In contrast, the conversion of pyruvate to acetyl-CoA is mainly regulated on a metabolic level by the in vivo activities of PFL and PDH. The ratio of in vitro to in vivo activities is in the range of 1 to 1.5 for PK, 5 to 17 for PFL and 5 to 80 for PDH under the experimental conditions. The regulation of in vivo activity and synthesis of these enzymes is sensitive to fluctuations of culture conditions, leading to oscillations of both the in vitro and in vivo activities. In particular, PFL is strongly affected during oscillations; its average in vitro activity is only about half of its corresponding steady-state value under similar environmental conditions. The average in vitro activities of PDH and PK under oscillations are close to their corresponding steady-state values. In contrast to all other enzymes measured for the glycerol metabolism by K. pneumoniae PFL and PDH are more effectively in vivo utilized under oscillations than under steady state, underlining the peculiar role of pyruvate metabolism in the dynamic responses of the culture.

Acetyltransferases↗
PubMed1998

Kinetic, dynamic, and pathway studies of glycerol metabolism by Klebsiella pneumoniae in anaerobic continuous culture: III. Enzymes and fluxes of glycerol dissimilation and 1,3-propanediol formation.

The initial steps of glycerol dissimilation and 1,3-propanediol (1, 3-PD) formation by Klebsiella pneumoniae anaerobically grown on glycerol were studied by quantifying the in vitro and in vivo activities of enzymes in continuous culture under conditions of steady state and oscillation and during transient phases. The enzymes studied included glycerol dehydrogenase (GDH), glycerol dehydratase (GDHt), and 1,3-propanediol oxidoreductase (PDOR). Three conclusions can be drawn from the steady-state results. First, glycerol concentration in the culture is a key parameter that inversely affects the in vitro activities (concentrations) of all three enzymes, but has a positive effect on their in vivo activities. Growth rate significantly affects the ratio of in vitro and in vivo enzyme activities under low glycerol concentrations, but not under glycerol excess. Second, whereas the flux through the oxidative pathway of glycerol dissimilation is governed mainly by the regulation of in vivo enzyme activity on a metabolic level, the flux through the reductive pathway is largely controlled by the synthesis of enzymes. Third, GDHt is a major rate-liming enzyme for the consumption of glycerol and the formation of 1,3-PD in K. pneumoniae at high glycerol concentrations. Results from oscillating cultures revealed that both in vitro and in vivo activities of the enzymes oscillated. The average values of the in vitro activities during an oscillation cycle agreed well with their corresponding values for nonoscillating cultures under similar environmental conditions. Experiments with step changes in the feed concentration of glycerol demonstrated that growth and product formation are very sensitive to changes of substrate concentration in the culture. This sensitivity is due to the dynamic responses of the genetic and metabolic networks. They should be considered when modeling the dynamics of the culture and attempting to improve the formation of 1,3-PD.

Alcohol Oxidoreductases↗
PubMed1998

Fermentation of glycerol to 1,3-propanediol and 2,3-butanediol by Klebsiella pneumoniae.

Klebsiella pneumoniae was shown to convert glycerol to 1,3-propanediol, 2,3-butanediol and ethanol under conditions of uncontrolled pH. Formation of 2,3-butanediol starts with some hours' delay and is accompanied by a reuse of the acetate that was formed in the first period. The fermentation was demonstrated in the type strain of K. pneumoniae, but growth was better with the more acid-tolerant strain GT1, which was isolated from nature. In continuous cultures in which the pH was lowered stepwise from 7.3 to 5.4, 2,3-butanediol formation started at pH 6.6 and reached a maximum yield at pH 5.5, whereas formation of acetate and ethanol declined in this p range 2,3-Butanediol and acetoin were also found among the products in chemostat cultures grown at pH 7 under conditions of glycerol excess but only with low yields. At any of the pH values tested, excess glycerol in the culture enhanced the butanediol yield. Both effects are seen as a consequence of product inhibition, the undissociated acid being a stronger trigger than the less toxic diols and acid anions. The possibilities for using the fermentation type described to produce 1,3-propanediol and 2,3-butanediol almost without by-products are discussed.

Acetic Acid↗
PubMed1997

Enzymatic evidence for an involvement of pyruvate dehydrogenase in the anaerobic glycerol metabolism of Klebsiella pneumoniae.

Stoichiometric analysis of pathways involved in anaerobic bioconversion of glycerol by Klebsiella pneumoniae revealed that enzyme(s) in addition to pyruvate formate-lyase (PFL) must be involved in pyruvate decarboxylation. In this work, enzymatic evidence is presented that confirmed a simultaneous involvement of pyruvate dehydrogenase complex (PDH) and excluded the presence of pyruvate:ferredoxin oxidoreductase in this anaerobic bioprocess. The in vitro PDH activity of cell extract from continuous culture was found to be strongly affected by the substrate (glycerol) concentration in medium and cell growth rate (dilution rate). It increases with increasing glycerol concentration and correlates well with the specific substrate uptake rate at different dilution rates in a kind of saturation function. At a similar substrate uptake rate, it decreases with cell growth rate. The in vitro activity of PDH is much higher than its in vivo activity calculated from the pathway stoichiometry but comparable to the calculated in vivo activity of PFL.

Anaerobiosis↗
PubMed1991

[Studies on manifestations of Rh-related hemolytic disease of the newborn in the years 1974-1989 in the Erfurt district].

In the course of 13 years (1977-1989) 223 of 223,121 liveborn infants in the district of Erfurt suffered from haemolytic disease due to Rh-isoimmunization, 0.1 per cent died. An initial drop of morbidity from 1.6 to 0.6 of 1000 newborns was followed by stagnation and further increase during the last years. More than 50% of the affected babies were delivered by women who had to be protected from sensibilization by immune prophylaxis. The cause for the immunization were deliveries (75%), miscarriages and interruptions (23%). The most important reason for the insufficient decrease of the Rh-morbidity is the failure of immune prophylaxis in the case of ABO-incongruence between mother and child. Our results support the demands for a general immune prophylaxis without taking into consideration the main blood groups and the number and result of the pregnancy. The quantity of severe erythroblastosis (7 stillborn and 5 hydropic liveborn) demonstrates the necessity to improve the prenatal management of these babies.

Abortion, Induced↗
PubMed1990

High cell density fermentation of recombinant Escherichia coli expressing human interferon alpha 1.

A defined medium was developed which, by means of a specific fed-batch mode, allows growth of the recombinant Escherichia coli strain TG1 (pBB210) up to a cell density of 60 g dry weight/l. Apart from glucose and aqueous ammonia fed as carbon and nitrogen sources, it was necessary to supply other nutrients or O2-enriched air. Aqueous ammonia also served for pH control. The pO2 level was kept at 20% saturation via closed-loop controls operating the two output variables of stirrer speed and glucose feeding rate. This fed-batch method prevented significant accumulation of acetate and other metabolic by-products. The recombinant E. coli expressed interferon alpha 1 more efficiently at a lower specific growth rate (muPr approximately 0.15 h-1) than at the maximum specific growth rate (mu max = 0.45 h-1). Therefore, fermentation in the batch phase at mu max was only allowed to continue up to a medium cell density. In the succeeding fed-batch phase, the specific growth rate was reduced to muPr by increasing the stirrer speed according to an empirically developed time scale.

Ammonia↗
PubMed1990

[Hygiene regimen in neonatology].

Prophylaxis of contamination, disinfection, sterilization of needed materials and sterile handling are essential suppositions for a successful struggle against hospital infections during the neonatal period. Proposals are presented to the hygienic management at delivery stations, delivery-rooms and neonatal intensive care units.

Cross Infection↗
PubMed1990

[Clinical aspects, diagnosis and therapy of nesidioblastosis].

Hyperinsulinemia due to an excessive secretion of insulin independent on normal regulation is the most frequent cause of persistent neonatal hypoglycemia. We report on clinical course, diagnostic procedures and treatment of nesidioblastosis in three patients. Main symptoms observed in newborn period were hypoglycemia, respiratory embarrassment, cyanosis and convulsions. Primary treatment was started by continuous infusion of glucose, administration of diazoxide and prednisolone or glucagon. Most important investigations were performed simultaneously. In all three children subtotal resection of pancreas was necessary, because there was no constant blood glucose level. Histological specimens confirmed diagnosis. In two of three patients pancreatectomy followed. One suffers from diabetes mellitus, the other one fed normally, has stable blood glucose level possibly due to existence of extrapancreatic insulin producing cells.

Child, Preschool↗
PubMed1990

[Diagnosis of muscle function in hereditary muscular dystrophies].

The evaluation of musclefunction im myopathies has been done upto now only by clinical trial. But in contrast in the field of medicine in sports has been proved the method of dynamometry of the muscles for a longer time which are necessary for objectivation of musclefunktion in myopathies. In this paper we present first results of health children and children suffering from Duchenne myopathy.

Adolescent↗