Biomedical subjects

G Schreiber

Publications and source records attributed to G Schreiber.

At least 91 records · Page 5Linked to original sources

PubMed1997

[Current aspects of hormone diagnosis in andrology--predictive values for the preservation of spermatogenesis].

The occurrence of hormonal disorders in 1.4 to 9.7% of the patients of andrology units justify a corresponding hormone analysis. Besides helping to make the differential-diagnosis of a disease hormone results are important for the description of preservation of spermatogenesis in cases of aspermia or azoospermia. Indications of a rest-spermatogenesis or a spermatozoon-pool could be crucial for assisted reproduction. Spermatological and testis-histological data of 2 independent collectives (n1 = 138; n2 = 110) were correlated with basal levels of FSH, LH, PRL, T, free T, and E2. Serum FSH appears with a sensitivity of 88.8% and a specification of 94.1% as good, but not absolutely certain discriminator of preserved or disturbed spermatogenesis. The inclusion of testis volume improves the diagnostic reliability only negligibly--the critical size is 16 ml. Because of its low diagnostic sensitivity the serum LH alone gives not much information but it can indicate together with serum testosterone causally relevant disorders in androgen metabolism (i.e. androgen resistance syndrome. Klinefelter-syndrome). PRL, T, free T, and E2 gave no conclusion of occurrence of disturbed or preserved spermatogenesis. For indication of performing testis biopsy because of diagnosis and therapeutic considerations further factors of spermatogenesis are required.

Adult↗

PubMed1996

Reduced beta-adrenergic receptor-coupled Gs protein function and Gs alpha immunoreactivity in mononuclear leukocytes of patients with depression.

beta-Adrenergic receptor-coupled Gs protein function was measured in 26 depressed patients through cholera toxin-sensitive, isoproterenol-induced increases in 3H-Gpp(NH)p binding capacity to mononuclear leukocytes (MNL). Highly significant reductions in receptor-coupled Gs protein function were observed in the depressed patients: 2.0 +/- 1.3% increases in guanine nucleotide-binding capacity, in comparison with the control group values of 28.3 +/- 6.9%. Similar reductions in Gs protein function were detected in both uni- and bipolar depressed patients. A significant negative correlation was found between receptor-coupled Gs protein measures and the severity of depression. Adding semiquantitative measures of MNL Gs alpha through immunoblot analysis by use of polyclonal antibodies against Gs alpha subunit, it was found that Gs alpha relative immunoreactivity was reduced from 100 +/- 2.0% in the control group of subjects to 75.9 +/- 2.3% in the depressed patients. We have previously described hyperfunctional Gs proteins in leukocytes of patients with mania. The present findings of reduced function of Gs in depressed patients suggests receptor-coupled Gs protein activity as a biochemical parameter indicatory of the affective state. Reduced receptor-coupled Gs protein function may reflect reduced levels of the beta-adrenergic receptor previously shown in leukocytes of depressed patients; however, our complementary immunoblot studies suggest a direct, postreceptor, quantitative, and functional reduction in Gs protein in MNL of depressed patients.

Adult↗

PubMed1996

Characterization of delta opioid receptors in lung cancer using a novel nonpeptidic ligand.

Cancer cells are often characterized by the presence of membrane receptors not normally associated with nontransformed cells from the same tissue type. Recent studies have demonstrated increased expression of high-affinity binding sites for opioid receptor-selective ligands in lung cancer cell lines relative to normal lung tissue. We investigated the binding of a nonpeptidic delta opioid receptor ligand in small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cells with the aim of developing the ligand as a novel lung cancer imaging agent. The ligand, [3H] (+)-4-[alpha-R)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3- hydroxybenzyl)-N,N-diethylbenzamide ([3H](+)BW373U86), bound with high-affinity [Kd (dissociation constant) = 0.066 +/- 0.012 nM] to membranes prepared from six different SCLC cell lines but not to those from seven NSCLC cell lines, including one mesothelioma. The number of biding sites varied from 10 to 300 fmol/mg membrane protein. Competition binding studies demonstrated displacement of [3H](+)BW373U86 binding by the delta-selective antagonists naltriben and 7-benzylidenenaltrexone but not with the mu- and kappa- selective antagonists D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 and trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]ben zeneacetamide methanesulfonate. Mean apparent Kis for naltriben and 7-benzylidenenaltrexone in membranes from two SCLC cell lines were 0.17 and 3.9 nM, respectively, but were >10 microM for the mu and kappa ligands. The nonselective antagonist naloxone displaced [3H](+)BW373U86 binding with an apparent Ki of approximately 29 nM. On the basis of these data, we believe the lung cancer receptor to be similar, if not identical, to the human brain delta opioid receptor. The lack of high-affinity [3H](+)BW373U86 binding in normal mouse lung membranes suggests a potential role for this ligand as a novel therapeutic or imaging agent.

Animals↗

PubMed1996

The crystal structure of transthyretin from chicken.

The crystal structure of chicken transthyretin has been solved at 290-pm resolution by molecular-replacement techniques. Transthyretin is the protein component of the amyloid fibrils found in patients suffering from either familial amyloidotic polyneuropathy or senile systemic amyloidosis. Familial amyloidotic polyneuropathy is an autosomal dominant hereditary type of amyloidosis which involves transthyretin with either one or two amino acid substitutions. The three-dimensional structure of chicken transthyretin was determined in order to compare a non-amyloidogenic, species-variant transthyretin with wild-type and mutant transthyretin molecules. Of the 31 chicken-to-human residue differences, 9 occur at positions which in human transthyretin give rise to amyloidogenic variants although none corresponds to the appropriate side-chain substitutions. The model of chicken transthyretin has been refined to an R-factor of 19.9%. The overall fold of the protein is that of an all-beta protein. Compared with wild-type human transthyretin the avian transthyretin shows quite large differences in the region known to be involved in binding to retinol-binding protein, it has a much shorter helical component than the human protein and some of the monomer-monomer interactions are different.

Animals↗

PubMed1996

Measurement of early events in signal transduction beyond receptors involving G proteins function in mononuclear leucocytes.

G protein function in human mononuclear leucocytes was measured through isoproterenol, carbamylcholine and dopamine-enhanced 3H-Gpp(NH)p binding. Dopamine and carbamylcholine exerted their effects through D5 and M2 receptors, respectively. ADP-ribosylation by bacterial toxins indicates that dopamine and isoproterenol affected Gs, while carbamylcholine affected Gi. Quantitative G proteins measures were conducted through immunoblot analyses with specific polyclonal antibodies against G alpha s, and G alpha i subunits. Simultaneous functional and quantitative measures of G proteins showed significant correlations between function and immunoreactivities. Agonist-enhanced guanine nucleotide exchange is thus suggested as a method for measurement of early events in signal transduction beyond receptors in leucocytes, which can potentially serve for detecting alterations in G proteins measures in human disease.

Adenylyl Cyclases↗

PubMed1996

Rapid, electrostatically assisted association of proteins.

The rapid association of barnase and its intracellular inhibitor barstar has been analysed from the effects of mutagenesis and electrostatic screening. A basal association rate constant of 10(5) M(-1) s(-1) is increased to over 5 x 10(9) M(-1) s(-1) by electrostatic forces. The association between the oppositely charged proteins proceeds through the rate-determining formation of an early, weakly specific complex, which is dominated by long-range electrostatic interactions, followed by precise docking to form the high affinity complex. This mode of binding is likely to be used widely in nature to increase association rate constants between molecules and its principles may be used for protein design.

Bacterial Proteins↗

PubMed1996

Wallaby serum amyloid A protein: cDNA cloning, sequence and evolutionary analysis.

A serum amyloid A (SAA) clone was isolated from a Tammar wallaby cDNA library, the most distantly related mammalian species for which an SAA has been described to date. The clone predicts a premolecule of 127 amino acids with good homology to other mammalian SAAs, and consists of an 18 residue leader peptide and a mature protein of 109 amino acids. Evolutionary analysis at both the protein and nucleotide level indicate that the wallaby SAA clone clusters with the acute phase SAAs. However, as the SAA superfamily has undergone concerted evolution it is not possible to determine at this point which acute phase SAA it is most like. The grouping of wallaby SAA inside the acute phase SAA cluster demonstrates that at least some of the duplication events giving rise to multiple acute phase genes occurred prior to the divergence of the eutherian and metatherian mammals.

Amino Acid Sequence↗

PubMed1996

Word associative production in affective versus schizophrenic psychoses.

The production of association word to stimulus words, which was found to be correlated with conceptual disorganization, as clinically measured by the Brief Psychiatric Rating Scale, was developed as a quantifiable measure of formal thought disorder. Associative word production in patients with affective psychoses (acute episodes of mania or schizoaffective disorder) was found to be higher in a statistically significant manner than in patients with acute episode of paranoid schizophrenia. The production of associative words in the two groups of acutely psychotic patients was significantly higher than in normal subjects, unipolar depressed, or residual schizophrenic patients. These quantitative differences reflected qualitative differences in the pattern of the production of word associations. Indeed, while patients with paranoid schizophrenia showed a sinusoidal-like type of oscillation in associative word production, patients with affective psychoses were characterized by exponential-like phases in associative word production. Associative word production may thus serve as a simple quantitative test for differentiating formal thought disorder in acute psychoses between patients with mania and patients with schizophrenia.

Adult↗

PubMed1996

Evolution of transthyretin gene expression in the liver of Didelphis virginiana and other American marsupials.

The occurrence of the thyroid hormone-binding plasma protein transthyretin in the bloodstream was investigated for four American marsupial species. Serum samples were analyzed by incubation with radioactive T4, followed by electrophoresis, then autoradiography, and Western blotting. Transthyretin was found in serum from Monodelphis domestica, Didelphis virginiana, Caluromys lanatus, and Dromiciops australis. For unambiguous identification, transthyretin from D, virginiana was purified from serum and its N-terminal amino acid sequence was determined. The obtained results suggest that the initiation of transthyretin gene expression in the liver of marsupials occurred independently in several lineages of American marsupials, all of which are at the ends of phylogenetic branches. The expression of the transthyretin gene in the liver of the American polyprotodont marsupials contrasts with the lack of transthyretin gene expression in the liver of all 22 previously investigated Australian Polyprotodonta.

Amino Acid Sequence↗

PubMed1996

FreeCall, a system for emergency-call-handling support.

This article describes a system for the optimization of the prehospital assessment of emergency, in cases involving thoraco-abdominal complaints and consciousness problems. This assessment is performed by nurses on the basis of a telephone interview at ambulance dispatch centers. The system has a body of biomedical and policy knowledge available to guide the interview and to provide advice.

Algorithms↗

PubMed1995

Characterization of in vitro oxidized barstar.

The polypeptide inhibitor of the ribonuclease barnase, barstar, has two cysteine residues in positions 40 and 82. These have been proposed to form a disulfide bridge leading to an increase in stability without changing the inhibitory activity of the protein. Barstar and a mutant (E80A) were oxidized in vitro and the biochemical and physico-chemical properties of the oxidized monomers were analysed. The oxidized proteins show no inhibition of barnase using a plate assay and are significantly destabilized. CD spectra indicate a loss of secondary structure. The amino acid substitution E80 --> A stabilizes the oxidized barstar to about the same extent as it does the reduced protein, indicating, however, that the helical region which it is in is intact.

Bacterial Proteins↗

PubMed1995

Binding of thyroxine to pig transthyretin, its cDNA structure, and other properties.

Thyroxine binding to proteins in pig plasma during electrophoresis was observed in the albumin, but not in the prealbumin and post-albumin regions. Transthyretin could be identified in medium from in vitro pig choroid plexus incubations by size and number of subunits and a very high rate of synthesis and secretion. Its electrophoretic mobility was intermediate between that of thyroxine-binding globulin and albumin. It bound thyroxine, retinol-binding protein, anti-(rat transthyretin) antibodies and behaved similarly to transthyretins from other vertebrate species when plasma was extracted with phenol. Inhibition experiments with the synthetic flavonoid F 21388, analysing the binding of thyroxine, suggested that transthyretin is not a major thyroxine carrier in the bloodstream of pigs. Cloning and sequencing of transthyretin cDNA from both choroid plexus and liver showed that the same transthyretin mRNA is expressed in pig choroid plexus and liver. The amino acid sequence derived from the nucleotide sequence revealed that pig transthyretin differs from the transthyretins of all other studied vertebrate species by an unusual C-terminal extension consisting of the amino acids glycine, alanine and leucine. This extension results from the mutation of a stop codon into a codon for glycine. The unusual C-terminal extensions do not seem to interfere with the access of thyroxine to its binding site in the central channel of transthyretin.

Amino Acid Sequence↗

PubMed1995

Energetics of protein-protein interactions: analysis of the barnase-barstar interface by single mutations and double mutant cycles.

The interaction of barnase, an extracellular RNase of Bacillus amylolique-faciens, with its intracellular inhibitor barstar is a suitable paradigm for protein-protein interactions, since the structures of both the free and the complexed proteins are available at high resolution. The contributions of residues from both proteins to the energetics of kinetics and thermodynamics of binding were measured by double mutant cycle analysis. Such cycles reveal whether the contributions from a pair of residues are additive, or the effects of mutations are coupled. The aim of the study was to determine which of the interactions are co-operative. Double mutant cycles were constructed between a subset of five barnase and seven barstar residues, which were shown by structural and mutagenesis studies to be important in stabilising the complex. The coupling energy between two residues was found to decrease with the distance between them. Generally, residues separated by less than 7 A interact co-operatively. At greater separations, the effects of mutation are additive, and the energetics of the interactions are independent of each other. The highest coupling energies are found between pairs of charged residues (1.6 to 7 kcal mol-1). Three of the six most important interactions detected by double mutant cycle analysis (with coupling energies of more than 3.0 kcal mol-1) had not been noted previously from examination of the crystal structure. The effects of mutation on the kinetics of association are all additive, apart from charged residues located at distances of up to 10 A apart, which are co-operative. This can be explained by the fact that the transition state for association occurs before most interactions are formed.

Bacterial Proteins↗

PubMed1995

A calorimetric study of the thermal stability of barstar and its interaction with barnase.

The temperature-induced unfolding of single, double, and triple mutants of barstar, the specific intracellular protein inhibitor of barnase from Bacillus amyloliquefaciens, has been studied by high-sensitivity differential scanning calorimetry. The thermal unfolding of barstar mutants, where at least one of the two cysteine residues in the molecule had been replaced by alanine, follows a two-state mechanism at neutral and alkaline pH. The unfolding enthalpy and heat capacity changes are slightly lower than those accepted for highly compact, small, globular proteins. We have found that at pH 2.5, where barstar seems to be in a molten globule state, the protein has a heat capacity between that of the native and the unfolded states and shows some tendency for association. Scanning calorimetry experiments were also extended to the barstar--barnase complex in the neutral and alkaline pH range. The binding constants obtained from DSC studies are similar to those already obtained from other (kinetic) studies. The interaction of barstar and barnase was also investigated by isothermal calorimetry in various buffers within the pH range 6.0-10.0 and a temperature range of 15-35 degrees C. The favorable enthalpy contribution to the binding is about 4 times higher than the entropic one at 25 degrees C. The overall data analysis of the combined calorimetric results has led to the thermodynamic characterization of barstar unfolding and the interaction of barstar and barnase over a wide range of temperatures.

Bacterial Proteins↗

PubMed1995

ppGpp-mediated regulation of DNA replication and cell division in Escherichia coli.

ppGpp serves as an alarmon in prokaryotes, distributing and coordinating different cellular processes according to the nutritional potential of the growth medium. This work is interpreted as favoring the view that, in addition to its previously documented role in regulating the rate of ribosome synthesis, ppGpp participates in coordinating DNA replication and cell division. We studied the effects of ppGpp on the cell division cycle, using cells containing plasmid pSM11 that codes for the 55-kDa truncated RelA protein under the inducible Ptac promoter. In this system it was found that the rate of initiation of new rounds of DNA replication is inversely correlated with the intracellular level of ppGpp. Furthermore, ppGpp levels similar to those found during the activation of stringent control inhibited replication initiation, in a manner comparable to that resulting from inhibition of protein synthesis by amino acid starvation or by chloramphenicol addition. However, in contrast to chloramphenicol treatment, elevated ppGpp levels did not block septum formation, and, in fact, there is some evidence for enhanced septation. As a result, the residual cell division following elevation in ppGpp levels was higher than after chloramphenicol treatment, resulting in cells with a size similar to that of stationary phase cells.

Cell Division↗

PubMed1995

Wallaby transthyretin.

A cDNA library was constructed from liver RNA of the Australian diprotodont marsupial Macropus eugenii, the Tammar wallaby. A cloned full-length transthyretin cDNA was sequenced. The derived amino-acid sequence showed 68% overall similarity to that of human transthyretin, with 86% similarity in the thyroxine binding site. Comparisons of nucleotide and amino acid sequences from several vertebrate species indicated that the greatest differences were in the region corresponding to the disordered N-terminus of mature human transthyretin. The evolutionary trees deduced from parsimony analyses of amino acid and nucleotide sequences of transthyretins, are consistent with that derived from fossil records.

Amino Acid Sequence↗

PubMed1995

The cerebral expression of plasma protein genes in different species.

The cerebrospinal fluid (CSF) contains the same proteins as blood plasma, but with a different pattern of concentrations. Protein concentrations in CSF are much lower than those in blood. CSF proteins are derived from blood or synthesized within the brain. The choroid plexus is an important source of CSF proteins. Transthyretin is the protein most abundantly synthesized and secreted by choroid plexus. It determines the distribution of thyroxine in the cerebral compartment. Synthesis of transthyretin first evolved in the brain, then later it became a plasma protein synthesized in the liver. Other proteins secreted by choroid plexus are serum retinol-binding protein, transferrin, caeruloplasmin, insulin-like growth factors, insulin-like growth factor binding proteins, cystatin C, alpha 1-antichymotrypsin, alpha 2-macroglobulin, prothrombin, beta 2-microglobulin and prostaglandin D synthetase. Species differences in expression of the genes for these proteins are outlined, and their developmental pattern, regulation and roles in the cerebral extracellular compartment are discussed.

Animals↗

PubMed1995

A case study in ontology library construction.

The goal of our work is to facilitate the development of medical knowledge-based systems by providing a library of reusable ontologies. The availability of such a library reduces the amount of knowledge acquisition required to create knowledge bases of new applications, and makes it easier to connect a knowledge-based system to existing data bases. This article presents a case study in constructing such a library. The emphasis is on studying the principles that underly the internal structure of the library as well as on the process of constructing and using the library. We envision that, in the future, application ontologies can be constructed by the selection and refinement of generic ontologies and domain ontologies from such a library.

Artificial Intelligence↗