PubMed Health⌕ Search

Biomedical subjects

R Wichmann

Publications and source records attributed to R Wichmann.

11 recordsLinked to original sources
PubMed2005

Cofactor regeneration at the lab scale.

Progress made in lab-scale applications of various coenzyme regeneration systems over the last two decades has mainly focused on the applications of NAD+/NADH- and NADP+/NADPH-dependent oxidoreductase reactions. In situ regeneration systems for these reactions, as well as whole cell, enzymatic, electro-enzymatic, chemical, and photochemical reactions are presented, including details about their efficiency and novelty. The progress of enzyme reaction engineering is also reported.

Bioreactors↗
PubMed2001

Ground-based observation of emission lines from the corona of a red-dwarf star.

All 'solar-like' stars are surrounded by coronae, which contain magnetically confined plasma at temperatures above 106 K. (Until now, only the Sun's corona could be observed in the optical-as a shimmering envelope during a total solar eclipse.) As the underlying stellar 'surfaces'-the photospheres-are much cooler, some non-radiative process must be responsible for heating the coronae. The heating mechanism is generally thought to be magnetic in origin, but is not yet understood even for the case of the Sun. Ultraviolet emission lines first led to the discovery of the enormous temperature of the Sun's corona, but thermal emission from the coronae of other stars has hitherto been detectable only from space, at X-ray wavelengths. Here we report the detection of emission from highly ionized iron (Fe XIII at 3,388.1 A) in the corona of the red-dwarf star CN Leonis, using a ground-based telescope. The X-ray flux inferred from our data is consistent with previously measured X-ray fluxes, and the non-thermal line width of 18.4 km s-1 indicates great similarities between solar and stellar coronal heating mechanisms. The accessibility and spectral resolution (45,000) of the ground-based instrument are much better than those of X-ray satellites, so a new window to the study of stellar coronae has been opened.

Journal Article↗
PubMed2000

Continuous enzymatic transformation in an enzyme membrane reactor with simultaneous NAD(H) regeneration. Reprinted from Biotechnology and Bioengineering, Vol. XXIII, No. 12, Pages 2789-2802 (1981).

Multienzyme reaction systems with simultaneous coenzyme regeneration have been investigated in a continuously operated membrane reactor at bench scale. NAD(H) covalently bound to polyethylene glycol with a molecular weight of 10(4) [PEG-10,000-NAD(H)] was used as coenzyme. It could be retained in the membrane reactor together with the enzymes. L-leucine dehydrogenase (LEUDH) was used as catalyst for the reductive amination of alpha-ketoisocaproate (2-oxo-4-methylpentanoic acid) to L-leucine. Formate dehydrogenase (FDH) was used for the regeneration of NADH. Kinetic experiments were carried out to obtain data which could be used in a kinetic model in order to predict the performance of an enzyme membrane reactor for the continuous production of L-leucine. The kinetic constants V(max) and k(m) of the enzymes are all in the same range regardless of whether native NAD(H) or PEG-10,000-NAD(H) is used as coenzyme. L-leucine was produced continuously out of alpha-ketoisocaproate for 48 days; a maximal conversion of 99.7% was reached. The space-time yield was 324 mmol/L day (or 42.5 g/L day).

Bioreactors↗
PubMed1998

Simulation of in situ subsurface biodegradation of polychlorophenols in air-lift percolators.

Air-lift percolator experiments simulated in situ subsurface degradation of 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol, in mixtures and individually, by indigenous microorganisms from a chlorophenol-contaminated aquifer. Inoculation with a chlorophenol(CP)-degrading gram-positive isolate from the CP-contaminated groundwater did not significantly increase CP degradation rates. Feed concentrations of up to 55 mg CP l-1 were degraded. Stable CP degradation was maintained for over 6 months. CP degradation rates up to 54.3 mg l-1 day-1 and effluent concentrations below 40 micrograms CP l-1 were achieved. CP were mineralized as shown by CP reduction, dissolved organic carbon removal and release of inorganic chloride.

Bacteria↗
PubMed1993

Spatial updating in Parkinson's disease.

We compared the ability of 48 patients with Parkinson's disease (PD) (24 mild, 24 moderate) and 35 controls to remain oriented to the starting position after being transported passively in a wheelchair in two conditions: visual and vestibular. The moderate PD group demonstrated the poorest performance in both sensory conditions. The visual condition discriminated between the mild PD group and the controls, but both groups had similar performance in the vestibular condition. Poor performance of the PD group in the visual condition and controls in the vestibular condition correlated significantly with poor performance on selected balance tests. Poor performance in the visual condition correlated significantly with poor performance on judgment of line orientation in the mild PD group. Spatial updating, or maintaining a sense of orientation while being moved in the environment, may be impaired in PD and should be investigated as a possible contributing factor to problems with spatial orientation noted clinically in some patients.

Aged↗
PubMed1984

A clinical comparison of aerosol and powder administration of beclomethasone dipropionate in childhood asthma.

Forty children with childhood asthma were conducted through a double-blind cross-over study to compare the effect of 400 micrograms beclomethasone dipropionate administered as aerosol and powder (Rotacaps). Children with severe asthma derived more benefit from the steroid administered as aerosol judged from their peak flow performance in the morning, although neither evening peak flow nor symptom scores revealed any difference. It is concluded that the Rotacaps are an advantageous supplement to available medication for the treatment of asthmatic children, although it should be observed that, using equal amounts of BDP, powder administration seems less effective than aerosol.

Adolescent↗
PubMed1980

Influence of substrate or product inhibition on the performance of enzyme reactors.

For the design of an enzyme reactor a detailed knowledge of the kinetic parameters of the catalyst under operational conditions is essential. For technical applications high initial substrate concentrations and high degrees of conversions are desirable, in order to save reactor volume and energy in recovery processes. Most of the kinetic data available in the literature have been derived from dilute solutions under initial rate conditions. These data cannot be extrapolated with confidence for technically interesting concentrations because substrate as well as product-inhibition may occur, which would not be observed in dilute solutions and by initial rate measurements. Because of this difficulty effective and fast methods to obtain significant data for technical applications have been developed based on-line rate determinations. Such extensive treatment has proved necessary for the following enzymes: alanine dehydrogenase, formate dehydrogenase and alpha-glucosidase, indicating that we are dealing with a general phenomenon.

Alanine Dehydrogenase↗
PubMed1980

Treatment of girls with excessive height prediction. Follow-up of forty girls treated with intramuscular estradiol and progesterone.

In a follow-up study of 40 tall girls treated with intramuscular estradiol and progesterone, the final height, bone age maturation, side effects and acceptance of treatment were evaluated. The mean duration of treatment was 18 months. During treatment, mean height increase was 6.5 cm (height velocity 3.7 cm/year), which is nearly 50% reduction of normal growth rate. The mean increase in bone age was 2.7 years (bone age velocity 1.8 years/year), which approximates twice the normal maturation rate. The mean reduction in final height was 5.0 cm as evaluated by the method of Bayley. Pinneau (BP), 2.9 cm by the method of Tanner et al. (TW) and 3.0 cm by the method of Roche et al. (RWT). The reduction was greatest when treatment was started before menarche, according to all three prediction methods. When treatment was started after menarch the calculated height reduction was greatest according to the BP method. There was good agreement between the three prediction methods in girls with a bone age below 12 years before treatment. In girls with a bone age above 12 years the height reduction by the BP method was much greater than when measured by the other methods. Side effects evaluated at follow-up were minimal and first menstruation occurred within 3 months (mean) after cessation of treatment. The number of pregnancies was estimated to be normal for age. All but three accepted the treatment. It is concluded that this type of treatment must be restricted to girls with severe psychological problems due to excessive height prognosis and selection for treatment must be based on an individualized evaluation.

Adolescent↗
PubMedDate not supplied

Steam sterilization--the response of the test pack.

The authors obtained temperature recordings from nearly 400 experiments with the standard test pack as defined in the prEN 285 as a basis for methods to evaluate conditions influencing steam sterilization. A new method to scale the duration and the extent of an air pocket (penetration fault) is presented. This method proved suitable for the interpretation and quantification of substantial correlations between the effect of a fault, the volume of the sterilizer chamber, and the rate of pressure change in the chamber. The coolest spot was found near the center of the test pack in only 17% of the tests. The air pocket was found to be an anomaly best elucidated by statistical methods. The prevailing influence of the rate of pressure change does not allow the establishment of limiting values for any fault, such as leakage rate or air dilution in the chamber, except as applied to a well-defined sterilizer. The penetration fault caused by an air leak does not depend on the chamber volume. The effects of residual air and induced air on the penetration fault are fundamentally different. Faults caused by those different air sources should be distinguished from each other even though both cause air pockets.

Evaluation Studies as Topic↗