PubMed Health⌕ Search

Biomedical subjects

R Brugger

Publications and source records attributed to R Brugger.

At least 19 recordsLinked to original sources

Expression pattern and localization of beta,beta-carotene 15,15'-dioxygenase in different tissues.

Beta,beta-carotene 15,15'-dioxygenase cleaves beta,beta-carotene into two molecules of retinal, and is the key enzyme in the metabolism of beta,beta-carotene to vitamin A. The enzyme has been known for more than 40 years, yet all attempts to purify the protein to homogeneity have failed. Recently, the successful cloning and sequencing of an enzyme with beta,beta-carotene 15,15'-dioxygenase activity from chicken, as well as from Drosophila, has been reported. Here, we describe in detail our attempt to enrich the chicken beta,beta-carotene 15,15'-dioxygenase to such an extent as to allow determination of partial amino acid sequences, which were then used to design degenerate oligonucleotides. Screening of a chicken duodenal expression library yielded a full-length clone containing a coding sequence of 1578 bp. Functional expression in Escherichia coli and in eukaryotic cell lines confirmed that we had cloned the first vertebrate dioxygenase that cleaves beta,beta-carotene at the central 15,15'-double bond. By performing a sequence homology search, the cDNA sequence of the mouse homologue was found as an expressed sequence tag (EST) in the gene bank. At the amino-acid level, the degree of homology between the chicken and mouse sequences is 81%. Thus beta,beta-carotene 15,15'-dioxygenase can be considered as being an enzyme that is evolutionarily rather well conserved. We established the expression pattern of beta,beta-carotene 15,15'-dioxygenase in chicken and mouse tissues with a combination of Northern blots and in situ hybridization. The mRNA for beta,beta-carotene 15,15'-dioxygenase was localized primarily in duodenal villi, as well as in liver and in tubular structures of lung and kidney. These new findings demonstrate that beta,beta-carotene 15,15'-dioxygenase is also expressed in epithelial structures, where it serves to provide the tissue-specific vitamin A supply.

Amino Acid Sequence↗

Expression, gene cloning, and characterization of five novel phytases from four basidiomycete fungi: Peniophora lycii, Agrocybe pediades, a Ceriporia sp., and Trametes pubescens.

Phytases catalyze the hydrolysis of phosphomonoester bonds of phytate (myo-inositol hexakisphosphate), thereby creating lower forms of myo-inositol phosphates and inorganic phosphate. In this study, cDNA expression libraries were constructed from four basidiomycete fungi (Peniophora lycii, Agrocybe pediades, a Ceriporia sp., and Trametes pubescens) and screened for phytase activity in yeast. One full-length phytase-encoding cDNA was isolated from each library, except for the Ceriporia sp. library where two different phytase-encoding cDNAs were found. All five phytases were expressed in Aspergillus oryzae, purified, and characterized. The phytases revealed temperature optima between 40 and 60 degrees C and pH optima at 5.0 to 6.0, except for the P. lycii phytase, which has a pH optimum at 4.0 to 5.0. They exhibited specific activities in the range of 400 to 1,200 U. mg, of protein(-1) and were capable of hydrolyzing phytate down to myo-inositol monophosphate. Surprisingly, (1)H nuclear magnetic resonance analysis of the hydrolysis of phytate by all five basidiomycete phytases showed a preference for initial attack at the 6-phosphate group of phytic acid, a characteristic that was believed so far not to be seen with fungal phytases. Accordingly, the basidiomycete phytases described here should be grouped as 6-phytases (EC 3.1.3.26).

6-Phytase↗

Cloning and expression of beta,beta-carotene 15,15'-dioxygenase.

beta,beta-Carotene 15,15'-dioxygenase cleaves beta-carotene into two molecules of retinal and is therefore the key enzyme in beta-carotene metabolism to vitamin A. In the present study, it was possible to enrich the chicken beta,beta-carotene 15,15'-dioxygenase to such an extent that partial amino acid sequence information could be obtained to design degenerate oligonucleotides. With RT-PCR a cDNA fragment could be obtained and used subsequently in a radioactive screening of a chicken duodenal expression library. We cloned the first eukaryotic beta,beta-carotene 15,15'-dioxygenase which symmetrically cleaves beta-carotene at the 15,15'-double bond.

Animals↗

From DNA sequence to improved functionality: using protein sequence comparisons to rapidly design a thermostable consensus phytase.

Naturally-occurring phytases having the required level of thermostability for application in animal feeding have not been found in nature thus far. We decided to de novo construct consensus phytases using primary protein sequence comparisons. A consensus enzyme based on 13 fungal phytase sequences had normal catalytic properties, but showed an unexpected 15-22 degrees C increase in unfolding temperature compared with each of its parents. As a first step towards understanding the molecular basis of increased heat resistance, the crystal structure of consensus phytase was determined and compared with that of Aspergillus niger phytase. Aspergillus niger phytase unfolds at much lower temperatures. In most cases, consensus residues were indeed expected, based on comparisons of both three-dimensional structures, to contribute more to phytase stabilization than non-consensus amino acids. For some consensus amino acids, predicted by structural comparisons to destabilize the protein, mutational analysis was performed. Interestingly, these consensus residues in fact increased the unfolding temperature of the consensus phytase. In summary, for fungal phytases apparently an unexpected direct link between protein sequence conservation and protein stability exists.

6-Phytase↗

Optimization of the catalytic properties of Aspergillus fumigatus phytase based on the three-dimensional structure.

Previously, we determined the DNA and amino acid sequences as well as biochemical and biophysical properties of a series of fungal phytases. The amino acid sequences displayed 49-68% identity between species, and the catalytic properties differed widely in terms of specific activity, substrate specificity, and pH optima. With the ultimate goal to combine the most favorable properties of all phytases in a single protein, we attempted, in the present investigation, to increase the specific activity of Aspergillus fumigatus phytase. The crystal structure of Aspergillus niger NRRL 3135 phytase known at 2.5 A resolution served to specify all active site residues. A multiple amino acid sequence alignment was then used to identify nonconserved active site residues that might correlate with a given favorable property of interest. Using this approach, Gln27 of A. fumigatus phytase (amino acid numbering according to A. niger phytase) was identified as likely to be involved in substrate binding and/or release and, possibly, to be responsible for the considerably lower specific activity (26.5 vs. 196 U x [mg protein](-1) at pH 5.0) of A. fumigatus phytase when compared to Aspergillus terreus phytase, which has a Leu at the equivalent position. Site-directed mutagenesis of Gln27 of A. fumigatus phytase to Leu in fact increased the specific activity to 92.1 U x (mg protein)(-1), and this and other mutations at position 27 yielded an interesting array of pH activity profiles and substrate specificities. Analysis of computer models of enzyme-substrate complexes suggested that Gln27 of wild-type A. fumigatus phytase forms a hydrogen bond with the 6-phosphate group of myo-inositol hexakisphosphate, which is weakened or lost with the amino acid substitutions tested. If this hydrogen bond were indeed responsible for the differences in specific activity, this would suggest product release as the rate-limiting step of the A. fumigatus wild-type phytase reaction.

6-Phytase↗

Stereoselective disposition of tiaprofenic acid enantiomers in rats.

The pharmacokinetics and metabolic chiral inversion of the S(+)- and R(-)-enantiomers of tiaprofenic acid (S-TIA, R-TIA) were assessed in vivo in rats, and in addition the biochemistry of inversion was investigated in vitro in rat liver homogenates. Drug enantiomer concentrations in plasma were investigated following administration of S-TIA and R-TIA (i.p. 3 and 9 mg/kg) over 24 hr. Plasma concentrations of TIA enantiomers were determined by stereospecific HPLC analysis. After administration of R-TIA it was found that 1) there was a time delay of peak S-TIA plasma concentrations, 2) S-TIA concentrations exceeded R-TIA concentrations from approximately 2 hr after dosing, 3) Cmax and AUC(0-infinity) for S-TIA were greater than for R-TIA following administration of S-TIA, and 4) inversion was bidirectional but favored inversion of R-TIA to S-TIA. Bidirectional inversion was also observed when TIA enantiomers were incubated with liver homogenates up to 24 hr. However, the rate of inversion favored transformation of the R-enantiomer to the S-enantiomer. In conclusion, stereoselective pharmacokinetics of R- and S-TIA were observed in rats and bidirectional inversion in rat liver homogenates has been demonstrated for the first time. Chiral inversion of TIA may involve metabolic routes different from those associated with inversion of other 2-arylpropionic acids such as ibuprofen.

Animals↗

Biochemical characterization of fungal phytases (myo-inositol hexakisphosphate phosphohydrolases): catalytic properties.

Supplementation with phytase is an effective way to increase the availability of phosphorus in seed-based animal feed. The biochemical characteristics of an ideal phytase for this application are still largely unknown. To extend the biochemical characterization of wild-type phytases, the catalytic properties of a series of fungal phytases, as well as Escherichia coli phytase, were determined. The specific activities of the fungal phytases at 37 degreesC ranged from 23 to 196 U. (mg of protein)-1, and the pH optima ranged from 2.5 to 7.0. When excess phytase was used, all of the phytases were able to release five phosphate groups of phytic acid (myo-inositol hexakisphosphate), which left myo-inositol 2-monophosphate as the end product. A combination consisting of a phytase and Aspergillus niger pH 2.5 acid phosphatase was able to liberate all six phosphate groups. When substrate specificity was examined, the A. niger, Aspergillus terreus, and E. coli phytases were rather specific for phytic acid. On the other hand, the Aspergillus fumigatus, Emericella nidulans, and Myceliophthora thermophila phytases exhibited considerable activity with a broad range of phosphate compounds, including phenyl phosphate, p-nitrophenyl phosphate, sugar phosphates, alpha- and beta-glycerophosphates, phosphoenolpyruvate, 3-phosphoglycerate, ADP, and ATP. Both phosphate liberation kinetics and a time course experiment in which high-performance liquid chromatography separation of the degradation intermediates was used showed that all of the myo-inositol phosphates from the hexakisphosphate to the bisphosphate were efficiently cleaved by A. fumigatus phytase. In contrast, phosphate liberation by A. niger or A. terreus phytase decreased with incubation time, and the myo-inositol tris- and bisphosphates accumulated, suggesting that these compounds are worse substrates than phytic acid is. To test whether broad substrate specificity may be advantageous for feed application, phosphate liberation kinetics were studied in vitro by using feed suspensions supplemented with 250 or 500 U of either A. fumigatus phytase or A. niger phytase (Natuphos) per kg of feed. Initially, phosphate liberation was linear and identical for the two phytases, but considerably more phosphate was liberated by the A. fumigatus phytase than by the A. niger phytase at later stages of incubation.

6-Phytase↗

Effect of clofibrate on the chiral disposition of ibuprofen in rats.

A potentially clinically important interaction has been described between clofibrate and ibuprofen in vitro. To determine whether this in vitro interaction is paralleled by a change in pharmacokinetics of ibuprofen in vivo two groups of rats were treated orally with clofibrate (n = 8, 280 mg/kg/day) or vehicle (n = 7) for 3 days. On day 3, 2 hr after the last dose of clofibrate, the rats were given an i.v. dose of pseudoracemic ibuprofen (20 mg/kg, 10 mg R-ibuprofen, 10 mg 13C-S-ibuprofen). Plasma concentrations of the enantiomers were monitored by a stereospecific gas chromatography mass spectrometry assay. The clearance of R-ibuprofen more than doubled in the clofibrate-treated group (mean +/- S.E.M.; 29.4 +/- 4.0 ml/min) as compared to control rats (13.0 +/- 1.4 ml/min; P = .003). This increase was similarly reflected in the clearance by inversion (treated, 23.2 +/- 3.2 ml/min, untreated, 10.0 +/- 1.2 ml/min; P = .003) and there was also an increase in the rate of inversion (treated, t1/2 inversion, 8.3 +/- 1.6 min; untreated, 13.9 +/- 1.4 min; P = .029). By contrast, the estimates of fractional chiral inversion were not affected by clofibrate and were in close agreement whether estimated by the area under the plasma concentration-time curve approach (treated, 0.79 +/- 0.02; untreated, 0.72 +/- 0.02) or by deconvolution (treated, 0.78 +/- 0.02; untreated, 0.73 +/- 0.02). There was a significant increase in volume of distribution at steady-state (treated, 4.42 +/- 1.12 liter/kg; untreated, 1.03 +/- 0.30 liter/kg; P = .017) observed for the R-enantiomer but not the S-enantiomer (treated, 1.04 +/- 0.13 liter/kg; untreated, 1.10 +/- 0.21 liter/kg). Pretreatment of rats with clofibrate significantly increased the concentrations of ibuprofen in fat, lung, brain and liver tissue. With respect to the protein levels of two key enzymes involved in chiral inversion, clofibrate pretreatment significantly induced expression of long chain acyl-coenzyme A synthetase, although the expression of the epimerase was unaltered. It is concluded, that clofibrate may increase the proportion of R-ibuprofen incorporated into long-lived lipid ("hybrid" lipid) stores.

Animals↗

Properties of prostacyclin synthase.

Prostacyclin synthase (PGIS) was isolated from bovine aortic microsomes after detergent solubilisation following purification by DEAE-Sephacel, immobilized metal affinity, and hydroxy apatite chromatography. The homogenous protein exhibited spectral characteristics of a heme-thiolate protein (P450) like the enzyme purified earlier from porcine microsomes and had an apparent mass of 52 kDa on SDS/PAGE. Three peptides from an endoproteinase Lys-C digest were isolated and sequenced. An antiserum was prepared from rabbits and purified by affinity chromatography. This allowed Western blots of microsomes from cultured endothelial cells. After treatment with IL-1 the activity of the cells in producing 6-keto-PGF1 alpha increased about threefold over 27 h which was accompanied by an increase in PGIS mass. A monoclonal antibody was used to set up an ELISA which served for the quantitation of PGIS in bovine tissues.

Amino Acid Sequence↗

The requirements and development of neutron beams for neutron capture therapy of brain cancer.

One of the two overriding conditions for successful BNCT is that there must be a sufficient number of thermal neutrons delivered to each of the boronated cells in the tumour bed (target volume). Despite the poor experience with BNCT in the USA some 40 years ago, the continued apparent success of BNCT in Japan since 1968, lead indirectly to the re-start of clinical trials on BNCT in 1994 at both Brookhaven and MIT. Similar trials will start soon at Petten in Europe. At other centres worldwide, many neutron beam designs are being proposed with either thermal or epithermal neutrons, emanating predominantly from nuclear research reactors. It is apparent that whilst the success of BNCT depends on a suitable neutron beam, there is a diversity in available designs, as well as each proposed type of neutron source, with consequently different characteristics of the emergent neutron beam. The paper presents the historical development of neutron beams used for BNCT, addresses the requirements on the types of beams, describes some of the existing designs and other proposals elsewhere and lastly, considers the broader requirements in designing NCT facilities. The focus of the paper is on treatment of brain cancer, neutron beam requirements for other types of cancer may vary.

Boron Neutron Capture Therapy↗

Effects of ibuprofen enantiomers and its coenzyme A thioesters on human prostaglandin endoperoxide synthases.

1. Ibuprofen enantiomers and their respective coenzyme A thioesters were tested in human platelets and blood monocytes to determine their selectivity and potency as inhibitors of cyclo-oxygenase activity of prostaglandin endoperoxide synthase-1 (PGHS-1) and PGHS-2. 2. Human blood from volunteers was drawn and allowed to clot at 37 degrees C for 1 h in the presence of increasing concentrations of the test compounds (R-ibuprofen, S-ibuprofen, R-ibuprofenoyl-CoA, S-ibuprofenoyl-CoA, NS-398). Immunoreactive (ir) thromboxane B2 (TXB2) concentrations in serum were determined by a specific EIA assay as an index of the cyclo-oxygenase activity of platelet PGHS-1. 3. Heparin-treated blood from the same donors was incubated at 37 degrees C for 24 h with the same concentrations of the test compounds in the presence of lipopolysaccharide (LPS, 10 microg ml[-1]). The contribution of PGHS-1 was suppressed by pretreatment of the volunteers with aspirin (500 mg; 48 h before venepuncture). As a measure of LPS induced PGHS-2 activity immunoreactive prostaglandin E2 (irPGE2) plasma concentrations were determined by a specific EIA assay. 4. S-ibuprofen inhibited the activity of PGHS-1 (IC50 2.1 microM) and PGHS-2 (IC50 1.6 microM) equally. R-ibuprofen inhibited PGHS-1 (IC50 34.9) less potently than S-ibuprofen and showed no inhibition of PGHS-2 up to 250 microM. By contrast R-ibuprofenoyl-CoA thioester inhibited PGE2 production from LPS-stimulated monocytes almost two orders of magnitude more potently than the generation of TXB2 (IC50 5.6 vs 219 microM). 5. Western blotting of PGHS-2 after LPS induction of blood monocytes showed a concentration-dependent inhibition of PGHS-2 protein expression by ibuprofenoyl-CoA thioesters. 6. These data confirm that S-ibuprofen represents the active entity in the racemate with respect to cyclo-oxygenase activity. More importantly the data suggest a contribution of the R-enantiomer to therapeutic effects not only by chiral inversion to S-ibuprofen but also via inhibition of induction of PGHS-2 mediated by R-ibuprofenoyl-CoA thioester. 7. The data may explain why racemic ibuprofen is ranked as one of the safest non-steroidal anti-inflammatory drugs (NSAIDs) so far determined in epidemiological studies.

Blood Platelets↗

Molecular cloning and expression of a 2-arylpropionyl-coenzyme A epimerase: a key enzyme in the inversion metabolism of ibuprofen.

The 2-arylpropionic acid derivatives, including ibuprofen, are the most widely used anti-inflammatory analgesic cyclooxygenase inhibitors. The (-)-R-enantiomer, which is inactive in terms of cyclooxygenase inhibition, is epimerized in vivo via the 2-arylpropionyl-coenzyme A (CoA) epimerase to the cyclooxygenase-inhibiting (+)-S-enantiomer. The molecular biology of the epimerization pathway is largely unknown. To clarify this mechanism, the sequence of the 2-arylpropionyl-CoA epimerase was identified, and the enzyme cloned and expressed. A cDNA clone encoding the 2-arylpropionyl-CoA epimerase was isolated from a rat liver cDNA library. The nucleotide and the deduced amino acid sequence of this enzyme was determined. Significant amino acid sequence similarity was found between the rat epimerase and carnitine dehydratases from Caenorhabditis elegans (41%) and Escherichia coli (27%). A bacterial expression system (E. coli strain M15[pREP4]) was used to express the epimerase protein, representing up to 20-30% of the total cellular E. coli protein. The expression of the epimerase was confirmed with Western blots using specific anti-epimerase antibodies and by measuring the rate of inversion of (R)-ibuprofenoyl-CoA. Northern blot analysis revealed a prominent 1.9-kb mRNA transcript in different rat tissues. In addition to its obvious importance in drug metabolism, the homology of the epimerase with carnitine dehydratases from several species suggests that this protein, which up to now has only been characterized as having a role in drug transformation, has a function in lipid metabolism.

Amino Acid Sequence↗

Isolation and characterization of rat liver microsomal R-ibuprofenoyl-CoA synthetase.

Microsomal long-chain acyl-CoA synthetase (EC 6.1.2.3.) has been suggested to be involved in the stereoselective formation of the CoA thioester of ibuprofen. In this study, we demonstrated that the microsomal enzyme from rat liver responsible for palmitoyl-CoA synthesis also catalyzes the formation of R-ibuprofenoyl-CoA in a Mg(2+)- and ATP-dependent process. Long-chain acyl-CoA synthetase from rat liver microsomes was purified to homogeneity as evidenced by SDS-gel electrophoresis. Simultaneous measurements of palmitoyl-CoA and R-ibuprofenoyl-CoA formation with HPLC in various fractions and purification steps during protein isolation revealed a high correlation between both activities. The purification procedure included solubilization of the microsomes obtained from rat livers with Triton X-100 and subsequent chromatography of the 100,000 x g supernatant on blue-sepharose, hydroxyapatite, and phosphocellulose. The purified enzyme exhibited an apparent molecular weight of 72 kDa as estimated by SDS gel electrophoresis, with specific activities of 71 nmol.min-1.mg-1 protein and 901 nmol.min-1.mg-1 protein for formation of R-ibuprofenoyl-CoA and palmitoyl-CoA, respectively. Palmitoyl-CoA formation catalyzed by the purified enzyme exhibited biphasic kinetics indicative of two isoforms, a high-affinity (KM 0.13 +/- 0.11 microM), low-capacity form and a low-affinity (KM 81 +/- 11.5 microM), high-capacity form. In contrast, measurement of R-ibuprofenoyl-CoA synthesis over a concentration range from 5 to 3000 microM showed the participation of a single CoA ligase with a KM of 184 +/- 19 microM, corresponding to the low-affinity isoform of palmitoyl-CoA synthesis with a marked enantioselectivity towards the R-form of ibuprofen. R-ibuprofenoyl-CoA formation of the enzyme preparation was inhibited by palmitic acid (KI 13.5 +/- 0.5 microM) and S-ibuprofen (KI 405 +/- 10 microM). In summary, these data give strong evidence for the identity of R-ibuprofenoyl-CoA and long-chain acyl-CoA synthetase.

Animals↗

Regulation of prostanoid-synthesis in the cardiovascular system.

Thromboxane A2 and prostacyclin are the two prostanoids involved in the regulation of the vascular tone. Their release is controlled by the activity of cyclooxygenase which has made this enzyme a preferred pharmacological target. We here report on the distribution of the two isoforms of cyclooxygenase in cultured mesangial cells and on a selective inhibitor of the cytokine-inducible cyclooxygenase-2. We also comment on the structure of thromboxane and prostacyclin synthase and their regulation under physiological and pathophysiological conditions.

Amino Acid Sequence↗

Isolation and molecular cloning of prostacyclin synthase from bovine endothelial cells.

Prostacyclin synthase catalyzes the conversion of prostaglandin H2 to prostacyclin, which is a powerful vasodilator and the most potent natural occurring inhibitor of platelet aggregation. In the present study, we determined the amino acid sequence of bovine prostacyclin synthase by combined protein chemical and molecular cloning techniques. The enzyme was purified and characterized from bovine aorta microsomes, and the partial amino acid sequences were determined with the native enzyme and endoproteinase Lys-C-cleaved peptides. Using primers synthesized according to the amino acid sequences, cDNA coding for prostacyclin synthase was amplified by polymerase chain reaction with bovine endothelial cell poly(A)+ RNA and cloned into pBluescript II. Nucleotide sequence analyses of the cloned cDNA inserts revealed that cDNA for this enzyme contained a 1500-base pair open reading frame coding for a 500-amino acid polypeptide with a M(r) of 56,628. COS-7 cells transfected with an expression plasmid harboring this cDNA clone expressed prostacyclin synthase activity. The primary structure of the enzyme showed structural characteristics of cytochrome P450 and exhibited a 32% identity to that of human cholesterol 7 alpha-hydroxylase. However, the identity between the amino acid sequences of bovine prostacyclin synthase and human thromboxane synthase was only 16%, and no P450 showed an identity higher than 40%, suggesting that prostacyclin synthase represents a new family in the P450 superfamily. RNA blot analysis indicated that the mRNA for prostacyclin synthase from bovine endothelial cells showed a size of approximately 2.7 kilobases and that the mRNA level increased about 3-fold by treatment of tumor necrosis factor-alpha.

Amino Acid Sequence↗

Characterization of monoclonal antibodies generated against bovine and porcine prostacyclin synthase and quantitation of bovine prostacyclin synthase.

Monoclonal antibodies were raised against prostacyclin synthases purified from bovine and porcine aortae, respectively. Two monoclonal antibodies, RS1 and RS2, were purified and characterized. As shown by enzyme activity precipitation and Western blot analysis, in solubilized bovine and porcine aortae microsomes the monoclonal antibodies reacted only with prostacyclin synthase. The monoclonal antibody RS1 cross-reacts with partially purified prostacyclin synthase from human umbilical veins in an ELISA-based assay. None of the antibodies inhibited the enzyme activity. By combination of the monoclonal antibody RS2 with a polyclonal antibody we established an enzyme-linked immunosorbent assay (ELISA) for quantitation of bovine prostacyclin synthase. ELISA data were confirmed by Western blot analysis. Among different bovine tissues, aortae with 1665 +/- 200 ng/mg microsomal protein showed the highest content of PGIS. Significant lower concentrations were observed in tongue, lung, kidney and thymus ranging from 49 +/- 13.4 to 2.7 +/- 0.9 ng/mg protein. The monoclonal antibody RS1 binds to endothelial cells and vascular smooth muscle cells in human liver tissue.

Animals↗