Carrier-induced localization in In-Ga-As/In-Ga-As-P separate-confinement quantum-well structures.
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Journal Article↗
Biomedical subjects
G Fuchs
Publications and source records attributed to G Fuchs.
Recent advances in the treatment of childhood obesity.
The multidisciplinary, four-phase approach, which includes PSMF, BEM, and MPE is successful in treating mild, moderate, and severe degrees of childhood and adolescent obesity. The MPE program is appropriate for use with PSMF and BEM due to its progressive nature, variety of options, and moderate intensity level. In addition, the MPE program is of sufficient intensity, duration, and frequency to promote a significant increase in estimated aerobic capacity (VO2max) and to promote the maintenance of lean body mass and resting energy expenditure. The short-term intervention of PSMF, BEM, and MPE also results in an improvement in body composition, lipid profiles, and IGF-1 and T3 levels. The 1200-calorie balanced diet, MPE, and BEM also provide a successful method of weight maintenance in children and adolescents, as indicated by further improvement in body composition at the 26-week measure. Additional studies are needed to assess the contribution of exercise to the maintenance of lean body mass and resting energy expenditure in obese children and adolescents. In addition, it will be important to assess long-term weight maintenance in obese adolescents who effectively lose weight in this multidisciplinary program.
Adolescent↗
Direct-to-indirect energy-gap transition in strained GaxIn1-xAs/InP quantum wells.
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Journal Article↗
Retrobiosynthetic analysis of carbon fixation in the phototrophic eubacterium Chloroflexus aurantiacus.
The phototrophic bacterium Chloroflexus aurantiacus does not use any of the known autotrophic CO2 fixation pathways. There is evidence for a new cyclic autotrophic pathway in which acetyl-CoA is converted to 3-hydroxypropionate and further to succinate and malate. This hypothesis was tested by feeding growing cultures during several generations with 3-hydroxy[1-13C]propionate, [1-13C]acetate, or [2-13C]acetate, in addition to unlabeled CO2. The relative 13C content of individual carbon atoms in biosynthetic amino acids and nucleosides was determined by 1H- and 13C-NMR spectroscopy. 13C coupling patterns were analyzed by two-dimensional 13C-TOCSY experiments which were optimized for the analysis of multiply 13C-labeled biosynthetic samples. From the 13C enrichments of amino acids and nucleosides, the labeling patterns of central metabolic intermediates were evaluated by a retrobiosynthetic approach. Both 3-hydroxypropionate and acetate were incorporated into all central metabolic pools. The 13C labeling and coupling patterns suggest a novel carbon fixation pathway via 3-hydroxypropionate. Specifically, we propose that acetyl-CoA is carboxylated to malonyl-CoA which is reduced under formation of 3-hydroxypropionyl-CoA. Dehydration and reduction yield propionyl-CoA which is converted to succinate by a second carboxylation reaction. The net product of autotrophic carbon fixation appears to be glyoxylate. However, it is not yet known how glyoxylate is channeled into anabolic metabolism. Assimilation of acetate can proceed via the CO2 fixation pathway, but also via the glyoxylate pathway.
Acetates↗
Enzymes of a novel autotrophic CO2 fixation pathway in the phototrophic bacterium Chloroflexus aurantiacus, the 3-hydroxypropionate cycle.
The phototrophic bacterium Chloroflexus aurantiacus can grow autotrophically but seems not to assimilate CO2 via any of the known autotrophic pathways. Holo [Holo, H. (1989) Arch. Microbiol. 151, 252-256] proposed a new pathway in which 3-hydroxypropionate is formed from acetyl-CoA. Previous studies excluded the operation of known CO2 fixation pathways and provided indirect evidence for the suggested pathway based on 13C-labelling experiments. Here all enzyme activities of the postulated cyclic CO2 fixation mechanism are demonstrated in vitro. In essence, acetyl-CoA is carboxylated and reductively converted via 3-hydroxypropionate to propionyl-CoA. Propionyl-CoA is carboxylated and converted via succinyl-CoA and CoA transfer to malyl-CoA. Malyl-CoA is cleaved to acetyl-CoA and glyoxylate. Thereby, the first CO2 acceptor molecule acetyl-CoA is regenerated, completing the cycle and the net CO2 fixation product glyoxylate is released. This cycle represents the fourth autotrophic pathway in nature and is designated the 3-hydroxypropionate cycle.
Acetyl Coenzyme A↗
Purification and properties of N5-methyltetrahydromethanopterin:coenzyme M methyltransferase from Methanobacterium thermoautotrophicum.
N5-Methyltetrahydromethanopterin:coenzyme M meth-yltransferase is an integral membrane protein found in methanogenic archaea. It catalyzes an energy-conserving step in methane formation from CO2 and from acetate. The enzyme from Methanobacterium thermoautotrophicum (strain Marburg) has been purified 30-fold to apparent homogeneity. The purified enzyme had an apparent molecular mass of 670 kDa and was composed of seven different polypeptides of 34 kDa, 28 kDa, 24 kDa, 23 kDa, 21 kDa, 13 kDa, and 12 kDa. The N-terminal amino acid sequences of these polypeptides were determined. The native 670-kDa enzyme was found to contain 7.6 mol 5-hydroxybenzimidazolyl cobamide/mol, 37 mol non-heme iron/mol and 34 mol acid-labile sulfur/mol. Cobalt analyses after sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed that the corrinoid was bound to the 23-kDa polypeptide. The apparent molecular masses of the polypeptides given above were determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis without boiling the samples prior to analysis. When the samples were boiled, as is usually done, the 23-kDa polypeptide changed its apparent molecular mass to 33 kDa and the 21-kDa, 24-kDa, and 28-kDa polypeptides formed aggregates. The specific activity (apparent Vmax) of the purified methyltransferase preparation was 11.6 mumol.min-1.mg protein-1. The apparent Km for N5-methyltetrahydromethanopterin was 260 microM and that for coenzyme M was 60 microM. The preparation was absolutely dependent on the presence of Ti(III) for activity. ATP enhanced the activity 1.5-2-fold.
Amino Acid Sequence↗
Enzymes of anaerobic metabolism of phenolic compounds. 4-Hydroxybenzoate-CoA ligase from a denitrifying Pseudomonas species.
The initial step of anaerobic 4-hydroxybenzoate and 3-hydroxybenzoate degradation was studied in a denitrifying Pseudomonas sp. 4'-Hydroxybenzoate and 3-hydroxybenzoate are converted into their coenzyme A (CoA) thioesters by two different specific coenzyme A ligases. 4-Hydroxybenzoate-CoA ligase (AMP-forming) was purified 350-fold. The ligase is active as a monomer of molecular mass 48 kDa, as determined by gel filtration and SDS/PAGE. At a pH optimum of 8.5, the apparent Km values for 4-hydroxybenzoate, ATP, and coenzyme A are 37 microM, 77 microM, and 125 microM, respectively. The enzyme reacts specifically with 4-hydroxybenzoate (100%) and 4-aminobenzoate (30%). Other analogues of benzoate, notably 3- or 2-hydroxybenzoate, are inactive, and 2,4-dihydroxybenzoate and 2-hydroxy-4-methylbenzoate act as competitive inhibitors (Ki = 1 microM). Polyclonal antibodies were raised and used in immunoblot assays to study the regulation of the expression of 4-hydroxybenzoate-CoA ligase. The ligase is synthesized when cells are grown anaerobically with 4-hydroxybenzoate, phenol, or p-cresol; phenol and p-cresol are degraded via 4-hydroxybenzoate. The enzyme is not present in cells grown aerobically with 4-hydroxybenzoate or anaerobically with benzoate or 4-hydroxyphenylacetate.
Amino Acid Sequence↗
Enzymes of anaerobic metabolism of phenolic compounds. 4-Hydroxybenzoyl-CoA reductase (dehydroxylating) from a denitrifying Pseudomonas species.
The reductive removal of aromatic hydroxyl functions plays an important role in the anaerobic metabolism of many phenolic compounds. We describe a new enzyme from a denitrifying Pseudomonas sp., 4-hydroxybenzoyl-CoA reductase (dehydroxylating), which reductively dehydroxylates 4-hydroxybenzoyl-CoA to benzoyl-CoA. The enzyme plays a role in the anaerobic degradation of phenol, 4-hydroxybenzoate, p-cresol, 4-hydroxyphenylacetate, and other aromatic compounds of which 4-hydroxybenzoyl-CoA is an intermediate. The enzyme is therefore induced only under anoxic conditions with these aromatic substrates, but not with benzoate or under aerobic conditions. A similar enzyme which reductively dehydroxylates 3-hydroxybenzoyl-CoA is induced during anaerobic growth with 3-hydroxybenzoate. The soluble enzyme 4-hydroxybenzoyl-CoA reductase was purified. It has a molecular mass of 260 kDa and consists of three subunits of 75, 35, and 17 kDa. The subunit composition is likely to be a2b2c2. The enzyme contains 12 mol iron/mol and 12 mol acid-labile sulfur/mol and exhibits a typical ultraviolet/visible spectrum of an iron-sulfur protein. The reaction requires a reduced electron donor such as reduced viologen dyes; no other co-catalysts are required, the product is benzoyl-CoA and oxidized dye. The reductase is rapidly inactivated by oxygen. The inactivation by low concentrations of cyanide or azide in a pseudo-first-order time course suggests that it may contain a transition metal in an oxidation state which reacts with these ligands. 4-Hydroxybenzoyl-CoA reductase represents a type of enzyme which is common in anaerobic aromatic metabolism of phenolic compounds. A similar enzyme is demonstrated in Rhodopseudomonas palustris anaerobically grown with 4-hydroxybenzoate. The biological significance of reductive dehydroxylation of aromatics and a possible reaction mechanism similar to the Birch reduction are discussed.
Amino Acid Sequence↗
Products of enzymatic reduction of benzoyl-CoA, a key reaction in anaerobic aromatic metabolism.
Benzoyl-coenzyme A is the most common central intermediate of anaerobic aromatic metabolism. Studies with whole cells of different bacteria and in vitro had shown that benzoyl-CoA is reduced to alicyclic compounds, possibly via cyclohexadiene intermediates. This reaction is considered a 'biological Birch reduction'. We have elucidated by NMR techniques the structures of six products of [ring-13C6]benzoate reduction. The reaction is catalyzed by extracts from cells of a denitrifying Pseudomonas strain K172 anaerobically grown with benzoate and nitrate as sole carbon and energy sources. The assay mixture contained [ring-13C6]benzoate plus traces of [U-14C]benzoate, Mg2+, ATP, coenzyme A (CoA), and Ti(III) as reductant. The use of the multiply 13C-labelled precursor increases the sensitivity of NMR detection and allows the analysis of crude product mixtures by two-dimensional coherence transfer procedures such as total correlation 13C-NMR spectroscopy and 13C-filtered 1H-NMR spectroscopy. The time course of product formation is consistent with the following order of events. Benzoyl-CoA is formed from benzoate via benzoate-CoA ligase. The first ring reduction product observed is cyclohex-1,5-diene-1-carboxyl-CoA. The next intermediate is 6-hydroxycyclohex-1-ene-1-carboxyl-CoA which is derived from the diene by addition of water. Part of the diene seems to be reduced to cyclohex-1-ene-1-carboxyl-CoA which becomes hydrated to trans-2-hydroxycyclohexane-1-carboxyl-CoA; these two intermediates may be side products in vitro. The first non-cyclic intermediate formed by beta-oxidation is 3-hydroxypimelyl-CoA. This aliphatic C7 dicarboxylic acid is proposed to be oxidized via glutaryl-CoA and crotonyl-CoA to three molecules of acetyl-CoA and one molecule of CO2. A similar product pattern was observed in the benzoate-degrading phototrophic bacterium Rhodopseudomonas palustris. This indicates that the enzymatic reduction of benzoyl-CoA may be mechanistically similar in different anaerobes.
Acyl Coenzyme A↗
Purification and characterization of phenylacetate-coenzyme A ligase from a denitrifying Pseudomonas sp., an enzyme involved in the anaerobic degradation of phenylacetate.
The enzyme catalysing the first step in the anaerobic degradation pathway of phenylacetate was purified from a denitrifying Pseudomonas strain KB 740. It catalyses the reaction phenylacetate + CoA + ATP-->phenylacetyl-CoA + AMP + PPi and requires Mg2+. Phenylacetate-CoA ligase (AMP forming) was found in cells grown anaerobically with phenylacetate and nitrate. Maximal specific enzyme activity was 0.048 mumol min-1 x mg-1 protein in the mid-exponential growth phase. After 640-fold purification with 18% yield, a specific activity of 24.4 mumol min-1 mg-1 protein was achieved. The enzyme is a single polypeptide with Mr of 52 +/- 2 kDa. The purified enzyme shows high specificity towards the aromatic inducer substrate phenylacetate and uses ATP preferentially; Mn2+ can substitute for Mg2+. The apparent Km values for phenylacetate, CoA, and ATP are 60, 150, and 290 microM, respectively. The soluble enzyme has an optimum pH of 8.5, is insensitive to oxygen, but is rather labile and requires the presence of glycerol and/or phenylacetate for stabilization. The N-terminal amino acid sequence showed no homology to other reported CoA-ligases. The expression of the enzyme was studied by immunodetection. It is present in cells grown anaerobically with phenylacetate, but not with mandelate, phenylglyoxylate, benzoate; small amounts were detected in cells grown aerobically with phenylacetate.
Adenosine Monophosphate↗
Anaerobic oxidation of phenylacetate and 4-hydroxyphenylacetate to benzoyl-coenzyme A and CO2 in denitrifying Pseudomonas sp. Evidence for an alpha-oxidation mechanism.
Anaerobic degradation of (4-hydroxy)phenylacetate in denitrifying Pseudomonas sp. was investigated. Evidence is presented for alpha-oxidation of the coenzyme A (CoA)-activated carboxymethyl side chain, a reaction which has not been described. The C6-C2 compounds are degraded to benzoyl-CoA and furtheron to CO2 via the following intermediates: Phenylacetyl-CoA, phenylglyoxylate, benzoyl-CoA plus CO2; 4-hydroxyphenylacetyl-CoA, 4-hydroxyphenylglyoxylate, 4-hydroxybenzoyl-CoA plus CO2, benzoyl-CoA. Trace amounts of mandelate possibly derived from mandelyl-CoA were detected during phenylacetate degradation in vitro. The reactions are catalyzed by (i) phenylacetate-CoA ligase which converts phenylacetate to phenylacetyl-CoA and by a second enzyme for 4-hydroxyphenylacetate; (ii) a (4-hydroxy)-phenylacetyl-CoA dehydrogenase system which oxidizes phenylacetyl-CoA to (4-hydroxy)phenylglyoxylate plus CoA; and (iii) (4-hydroxy)phenylglyoxylate: acceptor oxidoreductase (CoA acylating) which catalyzes the oxidative decarboxylation of (4-hydroxy)phenylglyoxylate to (4-hydroxy)benzoyl-CoA and CO2. (iv) The degradation of 4-hydroxyphenylacetate in addition requires the reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA, catalyzed by 4-hydroxybenzoyl-CoA reductase (dehydroxylating). The whole cell regulation of these enzyme activities supports the proposed pathway. An ionic mechanism for anaerobic alpha-oxidation of the CoA-activated carboxymethyl side chain is proposed.
Acyl Coenzyme A↗
Purification of glutaryl-CoA dehydrogenase from Pseudomonas sp., an enzyme involved in the anaerobic degradation of benzoate.
Cell-free extracts of Pseudomonas sp. strains KB 740 and K 172 both contained high levels of glutaryl-CoA dehydrogenase when grown anaerobically on benzoate or other aromatic compounds and with nitrate as electron acceptor. These aromatic compounds have in common benzoyl-CoA as the central aromatic intermediate of anaerobic metabolism. The enzymatic activity was almost absent in cells grown aerobically on benzoate regardless whether nitrate was present. Glutaryl-CoA dehydrogenase activity was also detected in cell-free extracts of Rhodopseudomonas, Rhodomicrobium and Rhodocyclus after phototrophic growth on benzoate. Parallel to the induction of glutaryl-CoA dehydrogenase as measured with ferricenium ion as electron acceptor, an about equally high glutaconyl-CoA decarboxylase activity was detected in cell-free extracts. The latter activity was measured with the NAD-dependent assay, as described for the biotin-containing sodium ion pump glutaconyl-CoA decarboxylase from glutamate fermenting bacteria. Glutaryl-CoA dehydrogenase was purified to homogeneity from both Pseudomonas strains. The enzymes catalyse the decarboxylation of glutaconyl-CoA at about the same rate as the oxidative decarboxylation of glutaryl-CoA. The green enzymes are homotetramers (m = 170 kDa) and contain 1 mol FAD per subunit. No inhibition was observed with avidin indicating the absence of biotin. The N-terminal sequences of the enzymes from both strains are similar (65%).
Amino Acid Sequence↗
New aerobic benzoate oxidation pathway via benzoyl-coenzyme A and 3-hydroxybenzoyl-coenzyme A in a denitrifying Pseudomonas sp.
A denitrifying Pseudomonas sp. is able to oxidize aromatic compounds compounds completely to CO2, both aerobically and anaerobically. It is shown that benzoate is aerobically oxidized by a new degradation pathway via benzoyl-coenzyme A (CoA) and 3-hydroxybenzoyl-CoA. The organism grew aerobically with benzoate, 3-hydroxybenzoate, and gentisate; catechol, 2-hydroxybenzoate, and protocatechuate were not used, and 4-hydroxybenzoate was a poor substrate. Mutants were obtained which were not able to utilize benzoate as the sole carbon source aerobically but still used 3-hydroxybenzoate or gentisate. Simultaneous adaptation experiments with whole cells seemingly suggested a sequential induction of enzymes of a benzoate oxidation pathway via 3-hydroxybenzoate and gentisate. Cells grown aerobically with benzoate contained a benzoate-CoA ligase (AMP forming) (0.1 mumol min-1 mg-1) which converted benzoate but not 3-hydroxybenzoate into its CoA thioester. The enzyme of 130 kDa composed of two identical subunits of 56 kDa was purified and characterized. Cells grown aerobically with 3-hydroxybenzoate contained a similarly active CoA ligase for 3-hydroxybenzoate, 3-hydroxybenzoate-CoA ligase (AMP forming). Extracts from cells grown aerobically with benzoate catalyzed a benzoyl-CoA- and flavin adenine dinucleotide-dependent oxidation of NADPH with a specific activity of at least 25 nmol NADPH oxidized min-1 mg of protein-1; NADH and benzoate were not used. This new enzyme, benzoyl-CoA 3-monooxygenase, was specifically induced during aerobic growth with benzoate and converted [U-14C]benzoyl-CoA stoichiometrically to [14C]3-hydroxybenzoyl-CoA.
Acyl Coenzyme A↗
Subcutaneous recombinant human erythropoietin and autologous blood donation before coronary artery bypass surgery.
Conventional therapies with recombinant human erythropoietin (rHuEPO) to sustain preoperative autologous blood collection entail high doses of the drug at short intervals. To evaluate the efficacy of a single weekly dose of rHuEPO for autologous blood collection, we randomly assigned 24 male patients scheduled for coronary artery bypass surgery to receive 400 IU/kg rHuEPO subcutaneously once a week or iron only. Patients were examined weekly and a total of up to 4 units of autologous blood were obtained if the hemoglobin level exceeded 12 g/dL. Patients receiving rHuEPO had consistently higher hemoglobin values than those receiving iron only (P < 0.001). Consequently, more autologous red cells were obtained from this group (776 +/- 49 mL vs 682 +/- 91 mL; P < 0.05). One patient receiving rHuEPO and eight in the control group required homologous blood at surgery (P < 0.01). These results suggest that 400 IU/kg rHuEPO administered subcutaneously once a week efficiently stimulates erythropoiesis and compensates the hemoglobin decrease after autologous blood donation.
Blood Transfusion, Autologous↗
[Course of bacterial infections in high-dose therapy with clozapine].
The influence of neuroleptic drugs on body temperature regulation is well established. Even with atypical neuroleptic drugs such as clozapine, hyperthermia has been observed as well as the malignant neuroleptic syndrome. It is likely that the influence of clozapine affects the immune response. A case is reported in which afebrile angina tonsillaris and endocarditis developed, as a result of high-dosage therapy with clozapine over several years. Besides the special features of the course, differential diagnosis, therapy and possible influence on the body temperature and the immune response are discussed.
Adult↗
[Computer controlled brain death documentation in the intensive care unit].
An interactive, knowledge-based computer system for brain death documentation is presented. The specific exponents BRAINDEX R and G were realised by the software tool Personal Consultant Plus and the programming language Clipper, respectively. The strategies of conclusion were forward chaining for approximate evaluation of coma stages and backward chaining for analysing the brain death syndrome. BRAINDEX was developed for use with an IBM personal computer or compatible equipment. Systemic analyses were compared retrospectively with the data from clinical brain death protocols (n = 132) of 128 comatose patients (mean age 35.1 +/- 15.8 years) with a Glasgow Coma Score of 3. Identical classifications (system vs physician) were found in all patients without diagnosis of brain death (n = 35). Differences related to the findings of the physician were evaluated in lower numbers of the systemic positive diagnosis of brain death (82 vs 89) and higher numbers of impossibility of systemic evaluation (11 vs 2). These results were obtained by conclusions of the computer system drawn by restrictive systemic mechanisms to avoid false-negative diagnoses. The system therefore seems to be useful for documentation, consultation, and as a teaching instrument and data bank in brain death.
Adult↗
Gastrointestinal blood loss in older infants: impact of cow milk versus formula.
Concerns that consumption of whole cow milk (WCM) by older infants may result in excessive gastrointestinal blood loss and subsequent iron deficiency led us to perform a prospective, randomized study in 104 infants. Infants were assigned to receive WCM beginning at 6 months or one of three formulas beginning at 4-6 months of age and followed until 12 months of age. Gastrointestinal blood loss was similar for all groups, as determined by both qualitative (Hemoccult II) and quantitative testing (HemoQuant). There was no association between concentration of fecal hemoglobin and volume of WCM consumed or iron status by 12 months of age. Of eight infants (seven WCM, one formula) who became iron-depleted, none had excessive fecal hemoglobin excretion. When pooled and analyzed regardless of feeding group, fecal hemoglobin increased with age and was greater at 11 and 12 months than at younger ages. We conclude that although infants fed WCM are at increased risk of developing iron depletion, the iron insufficiency is not due to gastrointestinal blood loss. We further conclude, based on our sample of normal infants age 4-12 months, that fecal hemoglobin concentrations of 0.5-0.8 mg/g stool correspond to the upper limits of normal, values much lower than in adults.
Analysis of Variance↗
Novel aerobic 2-aminobenzoate metabolism. Nucleotide sequence of the plasmid carrying the gene for the flavoprotein 2-aminobenzoyl-CoA monooxygenase/reductase in a denitrifying Pseudomonas sp.
Pseudomonas KB 740 degrades 2-aminobenzoate aerobically via a chimeric pathway which combines characteristics of anaerobic and aerobic aromatic metabolism. Atypically, 2-aminobenzoyl-CoA is an intermediate, and the activated aromatic acid is not only hydroxylated but also reduced to an alicyclic compound in a single step. The bacterial strain possesses a small plasmid, pKB 740, which carries all essential information of this new pathway. Its total nucleotide sequence was determined. It consists of 8280 bp and contains the genes for the two initial enzymes of the pathway; 2-aminobenzoate-CoA ligase catalyzes the activation of the aromatic acid, and the flavoenzyme 2-aminobenzoyl-CoA monooxygenase/reductase catalyzes the hydroxylation (monooxygenase activity) and subsequent reduction (reductase activity) of the aromatic ring of 2-aminobenzoyl-CoA. Furthermore, five open reading frames (ORF) possibly coding for polypeptides are on the plasmid. Putative promoter sequences were found for two of the ORF. A nucleotide sequence able to form a possible termination loop was located downstream of the gene for 2-aminobenzoyl-CoA monooxygenase/reductase. This gene consists of 2190 bases. The deduced amino acid sequence of the protein (730 residues; calculated molecular mass of the native 729-residue protein, 83,559 Da) contains a consensus sequence for an FAD-binding site at the N-terminus and a possible NAD(P)H-binding site approximately 150 amino acid residues apart from the N-terminus. The monooxygenase/reductase shows low sequence similarity to the flavoprotein salicylate hydroxylase. Functional and evolutionary aspects of this work are discussed.
Amino Acid Sequence↗