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Biomedical subjects

Andreas Schmid

Publications and source records attributed to Andreas Schmid.

65 records · Page 4Linked to original sources
PubMed2002

Characterization of hematopoietic bone marrow in male professional cyclists by magnetic resonance imaging of the lumbar spine.

PURPOSE: To prospectively evaluate hematopoietic bone marrow of male professional cyclists in relation to performance data and laboratory data, and in comparison to age-matched healthy volunteers. MATERIALS AND METHODS: Twenty male cyclists and 44 volunteers (27 males and 17 females) were prospectively studied by magnetic resonance imaging (MRI) at high-field strength. A sagittal T1-weighted (T1-w) spin-echo (SE) sequence, a gradient-echo (GE) sequence with an echo time (TE) for out-of-phase (OOP) imaging, and a turbo inversion-recovery sequence with short inversion time (TIRM) for fat suppression was used. The averaged bone marrow signal intensity (SI) of three adjacent vertebrae was related to the signal of an adjacent nondegenerative disk. RESULTS: The cyclists revealed a significantly different SI as compared to male volunteers in the OOP (0.34 +/- 0.14 vs. 0.28 +/- 0.09, P < 0.05) and T1-w sequences (1.62 +/- 0.19 vs. 1.77 +/- 0.30, P < 0.05). Only in TIRM was there a significant difference compared to female volunteers (0.36 +/- 0.08 vs. 0.44 +/- 0.04, P < 0.01). MRI data of cyclists did not correlate to hemoglobin, erythrocyte, or reticulocyte counts; ferritin, relative heart volume, relative maximal power (rPmax; W/kg bw), or relative maximal oxygen consumption (VO(2)max). A borderline linear correlation was found for hematocrit (OOP: r = 0.42, P = 0.06; TIRM: r = 0.44, P = 0.06). CONCLUSION: Bone marrow hyperplasia is observed in male professional cyclists in the axial skeleton. The MR findings are probably independent of mechanically induced marrow edema. A multifactorial cause must be considered, as single laboratory and performance data did not appear to contribute significantly to these results.

Adult↗
PubMed2002

Increasing the microbial activity in activated sludge by the phenomenon of 'biological resonance.

Mechanical oscillations as well as electrical oscillations (e.g. in an electrical oscillatory circuit) can lead to resonance conditions by external agitation with the natural frequency of the system. During the microbial protein synthesis, the induction and repression mechanisms also cause oscillations in the form of varying protein concentrations. The aim of this work concentrates on an induced resonance case of the biological system, comparable with physical resonance phenomena, by external periodic stimulations. For this, system theoretical computer simulations with a structured genetic model were carried out, which built the theoretical fundament for describing the effect of 'Biological Resonance'. Based on that, lab-scale experiments using a mixed microbial culture (activated sludge) and skimmed milk as an inducing substrate revealed an enhanced microbial productivity of around 60%-75% compared to values of the productivity under steady-state conditions in a narrow range of process parameters. The optimum (resonance case) was confirmed by a repetition of the variation experiments and is characterised by a substrate supply period of approx. 18 min and a following starvation period of about 9 min. Long-term investigations under optimised process conditions indicate adaptation mechanisms of the microorganisms to evade the imposed stress conditions. The productivity will not remain constant without additional stimulation and declines to its original level. However, temporal modulation of the starvation period permanently increases the productivity (elevated catabolism) to about 60%, which was observed over a period of several weeks.

Biomass↗
PubMed2002

XOD-catalyzed ROS generation mobilizes calcium from intracellular stores in mouse pancreatic acinar cells.

In fura-2 loaded isolated mouse pancreatic acinar cells, xanthine oxidase (XOD)-catalyzed reactive oxygen species (ROS) generation caused an increase in the cytosolic Ca(2+) concentration ([Ca(2+)](i)) by release of Ca(2+) from intracellular stores. The ROS-induced Ca(2+) signals showed large variability in shape and time-course and resembled in part Ca(2+) signals in response to physiological secretagogues. ROS-induced Ca(2+) mobilization started at the luminal cell pole and spread towards the basolateral side in a wave manner. ROS-evoked Ca(2+) responses were not inhibited by the phospholipase C (PLC) inhibitor U73122 (10 microM). Neither 2-aminoethoxy-diphenylborate (2-APB) (70 microM) nor ryanodine (50 microM) suppressed ROS-evoked Ca(2+) release. ROS still released Ca(2+) when the endoplasmic reticulum Ca(2+)-ATPase was blocked with thapsigargin (1 microM), or when rotenone (10 microM) was added to release Ca(2+) from mitochondria. Our results suggest that pancreatic acinar cells ROS do not unspecifically affect Ca(2+) homeostasis. ROS primarily affect Ca(2+) stores located in the luminal cell pole, which is also the trigger zone for agonist-induced Ca(2+) signals. Release of Ca(2+) induces Ca(2+) waves carried by Ca(2+)-induced Ca(2+) release and produces thereby global Ca(2+) signals. Under oxidative stress conditions, the increase in [Ca(2+)](i) could be one mechanism contributing to an overstimulation of the cell which could result in cell dysfunction and cell damage.

Animals↗
PubMed2002

The use of enzymes in the chemical industry in Europe.

Many European chemical industries are in a phase of reorganization resulting in a general opening towards life sciences. Traditional chemical markets are served increasingly with products derived from bioprocesses or hybrid chemical/biocatalytic processes. Biocatalytic steps are already being used to produce a wide range of products, including agricultural chemicals, organics, drugs and plastic materials, to name but a few. Apart from the rapidly growing number of commercialized bioprocesses, a partial survey of exploratory activities points to future applications of enzymes in the European chemical industry, which will bring new products and technologies and, in some cases, replace traditional syntheses.

Biotechnology↗
PubMed2002

The production of fine chemicals by biotransformations.

Today, biocatalysis is a standard technology for the production of chemicals. An analysis of 134 industrial biotransformations reveals that hydrolases (44%) and redox biocatalysts (30%) are the most prominent categories. Most products are chiral (89%) and are used as fine chemicals. In the chemical industry, successful product developments involve on average a yield of 78%, a volumetric productivity of 15.5 g/(L.h) and a final product concentration of 108 g/L. By contrast, the pharmaceutical industry focuses on time-to-market. The implications of this for future research and development on biocatalysis are discussed.

Biotechnology↗
PubMed2002

Oxidative biotransformations using oxygenases.

Considerable progress has been made in manipulating oxidative biotransformations using oxygenases. Substrate acceptance, catalytic activity, regioselectivity and stereoselectivity have been improved significantly by substrate engineering, enzyme engineering or biocatalyst screening. Preparative biotransformations have been carried out to synthesize useful pharmaceutical intermediates or chiral synthons on the gram to several-hundred-gram scale, by use of whole cells of wild type or recombinant strains. The synthetic application of oxygenases in vitro has been shown to be possible by enzymatic or electrochemical regeneration of NADH or NADPH.

Biotransformation↗
PubMed2002

Hematological indices and iron status in athletes of various sports and performances.

PURPOSE: Alterations of the red blood cell system and iron metabolism can influence physical performance. On the other hand, exercise can influence hematological variables. The purpose of this epidemiological study was to investigate the characteristics of the red blood cell system and the iron metabolism in athletes of different sporting disciplines and at different levels of performance. METHODS: We studied 851 male subjects (747 athletes, 104 untrained controls). Hemoglobin (Hb), hematocrit (Hct), red blood cell count (RBC), iron, transferrin, ferritin (Fer), and haptoglobin were analyzed in standardized blood samples, obtained after 2 d of rest, considering levels of performance (internationally, nationally, locally competitive, and leisure time), distinctive sporting category (endurance- (END), strength- (POW), and mixed-trained (MIX)), and, within endurance athletes, distinctive disciplines (cycling (CYC) and running (RUN)). RESULTS: No difference was found between athletes and controls in Hb and Hct. Reduced Hb, Hct, and RBC levels were observed in END compared with POW and MIX. These findings can mainly be attributed to exercise-induced plasma volume expansion, and only to a lesser degree and in selected athlete populations to hemolysis, as low haptoglobin is only observed in RUN, not in CYC, suggesting that not exercise itself but the "traumatic" movement of running might trigger the destruction of red blood cells. Physical activity of increasing duration and workloads (leisure time compared with competitive athletes) leads to decreased Fer levels in athletes, disregarding their discipline, but more pronounced in RUN. CONCLUSION: Physical training itself has no significant effect on selected hematological variables in athletes compared with untrained controls. The specific type and duration of exercise is of major importance in the adaptations of the blood cell system and the iron metabolism.

Blood Chemical Analysis↗
PubMed2002

Blood volume and hemoglobin mass in endurance athletes from moderate altitude.

PURPOSE: To determine whether total hemoglobin (tHb) mass and total blood volume (BV) are influenced by training, by chronic altitude exposure, and possibly by the combination of both conditions. METHODS: Four groups (N = 12, each) either from locations at sea level or at moderate altitude (2600 m) were investigated: 1) sea-level control group (UT-0 m), 2) altitude control group (UT-2600 m), 3) professional cyclists from sea level (C-0 m), and 4) professional cyclists from altitude (C-2600 m). All subjects from altitude were born at about 2600 m and lived all their lives (except during competitions at lower levels) at this altitude. tHb and BV were determined by the CO-rebreathing method. RESULTS: VO2max (mL x kg(-1) x min(-1)) was significantly higher in UT-0 m (45.3 +/- 3.2) than in UT-2600 m (39.6 +/- 4.0) but did not differ between C-0 m (68.2 +/- 2.7) and C-2600 m (69.9 +/- 4.4). tHb (g x kg(-1)) was affected by training (UT-0 m: 11.0 +/- 1.1, C-0 m: 15.4 +/- 1.3) and by altitude (UT-2600 m: 13.4 +/- 0.9) and showed both effects in C-2600 m (17.1 +/- 1.4). Because red cell volume showed a behavior similar to tHb and because plasma volume was not affected by altitude but by training, BV (mL x kg(-1)) was increased in C-0 m (UT-0 m: 78.3 +/- 7.9; C-0 m: 107.0 +/- 6.2) and in UT-2600 m (88.2 +/- 4.8), showing highest values in the C-2600 m group (116.5 +/- 11.4). CONCLUSION: In endurance athletes who are native to moderate altitude, tHb and BV were synergistically influenced by training and by altitude exposure, which is probably one important reason for their high performance.

Adult↗
PubMed2002

Characterization and application of xylene monooxygenase for multistep biocatalysis.

Xylene monooxygenase of Pseudomonas putida mt-2 catalyzes multistep oxidations of one methyl group of toluene and xylenes. Recombinant Escherichia coli expressing the monooxygenase genes xylM and xylA catalyzes the oxygenation of toluene, pseudocumene, the corresponding alcohols, and the corresponding aldehydes, all by a monooxygenation type of reaction (B. Bühler, A. Schmid, B. Hauer, and B. Witholt, J. Biol. Chem. 275:10085-10092, 2000). Using E. coli expressing xylMA, we investigated the kinetics of this one-enzyme three-step biotransformation. We found that unoxidized substrates like toluene and pseudocumene inhibit the second and third oxygenation steps and that the corresponding alcohols inhibit the third oxygenation step. These inhibitions might promote the energetically more favorable alcohol and aldehyde dehydrogenations in the wild type. Growth of E. coli was strongly affected by low concentrations of pseudocumene and its products. Toxicity and solubility problems were overcome by the use of a two-liquid-phase system with bis(2-ethylhexyl)phthalate as the carrier solvent, allowing high overall substrate and product concentrations. In a fed-batch-based two-liquid-phase process with pseudocumene as the substrate, we observed the consecutive accumulation of aldehyde, acid, and alcohol. Our results indicate that, depending on the reaction conditions, product formation could be directed to one specific product.

Benzene Derivatives↗
PubMed2001

Changing the substrate reactivity of 2-hydroxybiphenyl 3-monooxygenase from Pseudomonas azelaica HBP1 by directed evolution.

The substrate reactivity of the flavoenzyme 2-hydroxybiphenyl 3-monooxygenase (EC, HbpA) was changed by directed evolution using error-prone PCR. In situ screening of mutant libraries resulted in the identification of proteins with increased activity towards 2-tert-butylphenol and guaiacol (2-methoxyphenol). One enzyme variant contained amino acid substitutions V368A/L417F, which were inserted by two rounds of mutagenesis. The double replacement improved the efficiency of substrate hydroxylation by reducing the uncoupled oxidation of NADH. With guaiacol as substrate, the two substitutions increased V(max) from 0.22 to 0.43 units mg(-1) protein and decreased the K'(m) from 588 to 143 microm, improving k'(cat)/K'(m) by a factor of 8.2. With 2-tert-butylphenol as the substrate, k'(cat) was increased more than 5-fold. Another selected enzyme variant contained amino acid substitution I244V and had a 30% higher specific activity with 2-sec-butylphenol, guaiacol, and the "natural" substrate 2-hydroxybiphenyl. The K'(m) for guaiacol decreased with this mutant, but the K'(m) for 2-hydroxybiphenyl increased. The primary structure of HbpA shares 20.1% sequence identity with phenol 2-monooxygenase from Trichosporon cutaneum. Structure homology modeling with this three-domain enzyme suggests that Ile(244) of HbpA is located in the substrate binding pocket and is involved in accommodating the phenyl substituent of the phenol. In contrast, Val(368) and Leu(417) are not close to the active site and would not have been obvious candidates for modification by rational design.

Amino Acid Sequence↗