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M Schubert

Publications and source records attributed to M Schubert.

At least 37 records · Page 2Linked to original sources
PubMed2001

MUSIC and aromatic residues: amino acid type-selective (1)H-(15)N correlations, III.

Amino acid type-selective experiments can help to remove ambiguities in automated assignment procedures for (15)N/(13)C-labeled proteins. Here we present five triple-resonance experiments that yield amino acid type-selective (1)H-(15)N correlations for aromatic amino acids. Four of the novel experiments are based on the MUSIC coherence transfer scheme that replaces the initial INEPT transfer and is selective for CH(2). The MUSIC sequence is combined with selective excitation pulses to create experiments for Trp (W-HSQC) as well as Phe, Tyr, and His (FYH-HSQC). In addition, an experiment selective for Trp H(epsilon1)-N(epsilon1) is presented. The new experiments are recorded as two-dimensional experiments and their performance is demonstrated with the application to a protein domain of 115 amino acids.

Algorithms↗
PubMed2001

[Subretinal microphotodiode array as replacement for degenerated photoreceptors?].

A survey is given on the status of developments, concerning a subretinal electronic microphotodiode array that aims at replacing degenerated photoreceptors. Various prototypes have been developed, tested, and implanted in various experimental animals up to 18 months. The fact that electrical responses were recorded from the visual cortex of pigs after electrical stimulation by subretinal electrodes and the fact that responses are also recorded in-vitro in degenerated rat retinae, shows the feasibility of this approach. However, there are a number of open questions concerning the biocompatibility, the long-time stability, and the type of transmitted image to be solved before application in patients can be considered.

Animals↗
PubMed2001

Electrical properties of a light-addressable microelectrode chip with high electrode density for extracellular stimulation and recording of excitable cells.

A light-addressable microelectrode chip with 3600 TiN electrodes was fabricated. Amorphous silicon (a-Si:H) serves as a photo conductor. The electrodes on the chip are addressed by a laser spot and electrical properties of the system are determined. DC measurements show a dark to bright dynamic of 10(6)-10(7). The AC impedance dynamic @ 1 kHz/100 mV and thus the signal-to-noise-ratio is determined to 60. This value is quite sufficient for electrophysiological measurements. For the first time, recordings from cardiac myocytes are reported using the principle of light-addressing. Measurements were done with a standard laser scan microscope (Zeiss LSM 410).

Electric Stimulation↗
PubMed2001

Remote F-wave changes after local botulinum toxin application.

OBJECTIVE: Although the therapeutic effects of botulinum toxin A can be explained by its action at the neuromuscular junction, central or more proximal effects have also been discussed. METHODS: Eleven patients with torticollis spasmodicus and 3 patients with writer's cramp were studied before and 1 and 5 weeks after the first treatment with botulinum toxin. We measured compound muscle action potentials (CMAPs), motor conduction velocities (MCVs), the shortest (SFL) and the mean F-wave latencies (MFL) and F-wave persistence (30 trials) of untreated muscles for each side (ulnar nerve-abductor digiti minimi muscle, peroneal nerve-tibialis anterior muscle). RESULTS: CMAPs and MCVs showed no significant changes. For both nerves, however, SFL and MFL were prolonged slightly 1 week after treatment and returned to about baseline after 5 weeks (t test). The F-wave persistence was reduced 1 week after treatment for the right ulnar and both peroneal nerves (t test). CONCLUSIONS: These results are not likely due to an impairment of neuromuscular transmission. Instead, we propose a decreased excitability of alpha-motoneurons supplying non-treated muscles. A reduction of muscle spindle activity or changes of the recurrent inhibition are discussed as possible causes.

Action Potentials↗
PubMed2001

Amino acid type-selective backbone 1H-15N-correlations for Arg and Lys.

Four novel amino acid type-selective triple resonance experiments to identify the backbone amino proton and nitrogen resonances of Arg and Lys and of their sequential neighbors in (13C,15N)-labeled proteins are presented: the R(i+1)-HSQC and R(i,i+1)-HSQC select signals originating from Arg side chains, the K(i+1)-HSQC and K(i,i+1)-HSQC select signals originating from Lys side chains. The selection is based on exploiting the characteristic chemical shifts of a pair of carbon atoms in Arg and Lys side chains using selective 90 degree pulses. The new experiments are recorded as two-dimensional 1H-15N-correlations and their performance is demonstrated with the application to a protein domain of 83 amino acids.

Animals↗
PubMed2001

Use of intralesional interferon-alpha for the treatment of recalcitrant oral warts in patients with AIDS: a report of 4 cases.

Four human immunodeficiency virus-positive homosexual men with 2- to 4.5-year histories of recurrent oral warts that had failed to respond to conventional surgical and other treatment modalities were offered treatment with interferon-alpha. All had multiple or large oral warts, 3 had skin warts, 2 had a history of anal warts, and 1 had penile lesions. All 4 patients were treated with a combination of intralesional and subcutaneous interferon-alpha. Adverse side effects were dose-related, mild, and transient; they included flulike symptoms (3 patients), hair loss and tachycardia (1 patient), and transient changes in the white blood cell count. All patients responded to therapy and remained free of disease up to 42 months. Intralesional injection with interferon-alpha appears to provide excellent clinical control for recurrent, multiple, and extensive oral warts in the human immunodeficiency virus-positive population, and is a useful adjunct to initial surgical removal of oral warts.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Requirement of specific intrahelical interactions for stabilizing the inactive conformation of glycoprotein hormone receptors.

Systematic analysis of structural changes induced by activating mutations has been frequently utilized to study activation mechanisms of G-protein-coupled receptors (GPCRs). In the thyrotropin receptor and the lutropin receptor (LHR), a large number of naturally occurring mutations leading to constitutive receptor activation were identified. Saturating mutagenesis studies of a highly conserved Asp in the junction of the third intracellular loop and transmembrane domain 6 suggested a participation of this anionic residue in a salt bridge stabilizing the inactive receptor conformation. However, substitution of all conserved cationic residues at the cytoplasmic receptor surface did not support this hypothesis. Asp/Glu residues are a common motif at the N-terminal ends of alpha-helices terminating and stabilizing the helical structure (helix capping). Since Asp/Glu residues in the third intracellular loop/transmembrane domain 6 junction are not only preserved in glycoprotein hormone receptors but also in other GPCRs we speculated that this residue probably participates in an N-terminal helix-capping structure. Poly-Ala stretches are known to form and stabilize alpha-helices. Herein, we show that the function of the highly conserved Asp can be mimicked by poly-Ala substitutions in the LHR and thyrotropin receptor. CD and NMR studies of peptides derived from the juxtamembrane portion of the LHR confirmed the helix extension by the poly-Ala substitution and provided further evidence for an involvement of Asp in a helix-capping structure. Our data implicate that in addition to well established interhelical interactions the inactive conformation of GPCRs is also stabilized by specific intrahelical structures.

Amino Acid Sequence↗
PubMed2000

Frataxin activates mitochondrial energy conversion and oxidative phosphorylation.

Friedreich's ataxia (FA) is an autosomal recessive disease caused by decreased expression of the mitochondrial protein frataxin. The biological function of frataxin is unclear. The homologue of frataxin in yeast, YFH1, is required for cellular respiration and was suggested to regulate mitochondrial iron homeostasis. Patients suffering from FA exhibit decreased ATP production in skeletal muscle. We now demonstrate that overexpression of frataxin in mammalian cells causes a Ca(2+)-induced up-regulation of tricarboxylic acid cycle flux and respiration, which, in turn, leads to an increased mitochondrial membrane potential (delta psi(m)) and results in an elevated cellular ATP content. Thus, frataxin appears to be a key activator of mitochondrial energy conversion and oxidative phosphorylation.

3T3 Cells↗
PubMed2000

Evolutionary conservation of the presumptive neural plate markers AmphiSox1/2/3 and AmphiNeurogenin in the invertebrate chordate amphioxus.

Amphioxus, as the closest living invertebrate relative of the vertebrates, can give insights into the evolutionary origin of the vertebrate body plan. Therefore, to investigate the evolution of genetic mechanisms for establishing and patterning the neuroectoderm, we cloned and determined the embryonic expression of two amphioxus transcription factors, AmphiSox1/2/3 and AmphiNeurogenin. These genes are the earliest known markers for presumptive neuroectoderm in amphioxus. By the early neurula stage, AmphiNeurogenin expression becomes restricted to two bilateral columns of segmentally arranged neural plate cells, which probably include precursors of motor neurons. This is the earliest indication of segmentation in the amphioxus nerve cord. Later, expression extends to dorsal cells in the nerve cord, which may include precursors of sensory neurons. By the midneurula, AmphiSox1/2/3 expression becomes limited to the dorsal part of the forming neural tube. These patterns resemble those of their vertebrate and Drosophila homologs. Taken together with the evolutionarily conserved expression of the dorsoventral patterning genes, BMP2/4 and chordin, in nonneural and neural ectoderm, respectively, of chordates and Drosophila, our results are consistent with the evolution of the chordate dorsal nerve cord and the insect ventral nerve cord from a longitudinal nerve cord in a common bilaterian ancestor. However, AmphiSox1/2/3 differs from its vertebrate homologs in not being expressed outside the CNS, suggesting that additional roles for this gene have evolved in connection with gene duplication in the vertebrate lineage. In contrast, expression in the midgut of AmphiNeurogenin together with the gene encoding the insulin-like peptide suggests that amphioxus may have homologs of vertebrate pancreatic islet cells, which express neurogenin3. In addition, AmphiNeurogenin, like its vertebrate and Drosophila homologs, is expressed in apparent precursors of epidermal chemosensory and possibly mechanosensory cells, suggesting a common origin for protostome and deuterostome epidermal sensory cells in the ancestral bilaterian.

Amino Acid Sequence↗
PubMed2000

Role of brain insulin receptor in control of body weight and reproduction.

Insulin receptors (IRs) and insulin signaling proteins are widely distributed throughout the central nervous system (CNS). To study the physiological role of insulin signaling in the brain, we created mice with a neuron-specific disruption of the IR gene (NIRKO mice). Inactivation of the IR had no impact on brain development or neuronal survival. However, female NIRKO mice showed increased food intake, and both male and female mice developed diet-sensitive obesity with increases in body fat and plasma leptin levels, mild insulin resistance, elevated plasma insulin levels, and hypertriglyceridemia. NIRKO mice also exhibited impaired spermatogenesis and ovarian follicle maturation because of hypothalamic dysregulation of luteinizing hormone. Thus, IR signaling in the CNS plays an important role in regulation of energy disposal, fuel metabolism, and reproduction.

Adipose Tissue↗
PubMed2000

IRS-2 pathways integrate female reproduction and energy homeostasis.

Severe dietary restriction, catabolic states and even short-term caloric deprivation impair fertility in mammals. Likewise, obesity is associated with infertile conditions such as polycystic ovary syndrome. The reproductive status of lower organisms such as Caenorhabditis elegans is also modulated by availability of nutrients. Thus, fertility requires the integration of reproductive and metabolic signals. Here we show that deletion of insulin receptor substrate-2 (IRS-2), a component of the insulin/insulin-like growth factor-1 signalling cascade, causes female infertility. Mice lacking IRS-2 have small, anovulatory ovaries with reduced numbers of follicles. Plasma concentrations of luteinizing hormone, prolactin and sex steroids are low in these animals. Pituitaries are decreased in size and contain reduced numbers of gonadotrophs. Females lacking IRS-2 have increased food intake and obesity, despite elevated levels of leptin. Our findings indicate that insulin, together with leptin and other neuropeptides, may modulate hypothalamic control of appetite and reproductive endocrinology. Coupled with findings on the role of insulin-signalling pathways in the regulation of fertility, metabolism and longevity in C. elegans and Drosophila, we have identified an evolutionarily conserved mechanism in mammals that regulates both reproduction and energy homeostasis.

Animals↗
PubMed2000

[Subcutaneous magnesium pump in a patient with combined magnesium transport defect].

HISTORY AND ADMISSION FINDINGS: A 28-year-old man, known to have abnormal intestinal magnesium absorption, presented with recurrent cerebral seizures. Despite daily intravenous sulphate infusions, magnesium concentration remained inadequate. Physical examination was unremarkable. INVESTIGATIONS: Serum magnesium concentration was markedly reduced to 0.48 mmol/l. The parenteral magnesium tolerance test indicated reduced enteric magnesium absorption of < 20%. Absolute magnesium concentration in 24-hour urine was normal at 6.3 mmol/24 h, but high in proportion to the hypomagnesaemia. All other laboratory data were within normal limits. TREATMENT AND COURSE: In addition to the known intestinal malabsorption the patient also had isolated renal loss of magnesium. It was only by continuous magnesium infusion with a recently developed portable subcutaneous pump system that normal serum magnesium concentrations were attained and all symptoms disappeared. CONCLUSION: This patient has combined magnesium transport defects, which could not be effectively treated by conventional methods, but required continuous magnesium infusion with an indwelling subcutaneous infusion pump. This case serves as an example of the way in which subcutaneous infusion can provide physiological substitution of electrolytes.

Adult↗
PubMed2000

Botulinum toxin treatment of cocontractions after birth-related brachial plexus lesions.

The authors studied botulinum toxin type A therapy of severe biceps-triceps cocontractions after nerve regeneration following birth-related brachial plexus lesions. Six children (age, 2 to 4 years) were treated two to three times over a period of 8 to 12 months with 40 mouse units of botulinum toxin at two sites of the triceps muscle. Elbow range of motion improved from 0 to 25 to 50 deg to 0 to 25 to 100 deg (p < 0.05), and muscle force of elbow flexion increased from a mean of Medical Research Council classification 1.7 to 3.7 (p < 0.05). After a 1-year follow-up, there was no clinical recurrence.

Birth Injuries↗
PubMed2000

Characterization of two amphioxus Wnt genes (AmphiWnt4 and AmphiWnt7b) with early expression in the developing central nervous system.

Full-length sequences and developmental expression patterns of two amphioxus Wnt genes (AmphiWnt4 and AmphiWnt7b) are described for the first time. The dynamic expression pattern of AmphiWnt4 suggests roles in the development of the posterior mesoderm, central nervous system, muscular somites, heart, and endostyle (a homolog of the vertebrate thyroid). The less diverse expression domains of AmphiWnt7b indicate that this gene may be involved only in the development of the central nervous system and the endostyle. In contrast to amphioxus, vertebrate embryos do not express Wnt4 homologues in the posterior mesoderm, somites, or heart; instead, Wnt genes of other subfamilies are expressed in these developing vertebrate organs. Because the developmental genetic programs of amphioxus may approximate those in the invertebrate chordate ancestor of the vertebrates, it is possible that some developmental functions of an ancestral Wnt4 gene may have been assumed by genes of other Wnt subfamilies during vertebrate evolution, possibly as a result of functional redundancy among Wnt subfamilies.

Amino Acid Sequence↗
PubMed2000

Analysis of non-covalent protein complexes up to 290 kDa using electrospray ionization and ion trap mass spectrometry.

Non-covalently-bound subunit complexes of proteins have been measured by an ion trap mass spectrometer equipped with an orthogonal electrospray ionization source. For the analysis of the generated molecular ions with high mass/charge ratios, the mass/charge range of the ion trap was extended by increasing its radio frequency (rf) voltage to 15 kV (V(0-p)) and by resonant ion ejection. Ions of the non-covalent dimer of bovine serum albumin (BSA), as well as of subunit complexes of alcohol dehydrogenase (ADH) from bakers' yeast and from horse liver, have been detected at mass/charge values between 3000-9000 Th. The maximum observed molecular weight was that of a non-covalently-bound subunit-octamer of bakers' yeast ADH (two non-covalently-bound subunit-tetramers) at ca. 290 kDa.

Alcohol Dehydrogenase↗
PubMed2000

Subthreshold prefrontal repetitive transcranial magnetic stimulation reduces motor cortex excitability.

The prefrontal cortex plays an important role in central motor control. We have examined whether prefrontal repetitive transcranial magnetic stimulation (rTMS) induces changes of motor cortex excitability determined by motor evoked potentials (MEPs) following single-pulse TMS. We studied 18 healthy volunteers stimulated at 5 Hz with 10% subthreshold prefrontal vs. occipital rTMS for 12 s. MEPs from the flexor carpi radialis muscle after single-pulse vertex stimulation were recorded during rTMS at 0, 4, 8, and 12 s. MEP areas decreased significantly after 8 s of prefrontal rTMS (P < 0. 05) but not after occipital rTMS. We conclude that rTMS of the prefrontal cortex may inhibit the primary motor areas.

Adult↗
PubMed2000

Characterization of an amphioxus wnt gene, AmphiWnt11, with possible roles in myogenesis and tail outgrowth.

The full-length sequence and developmental expression of an amphioxus Wnt gene (AmphiWnt11) are described. A phylogenetic analysis of all known full-length Wnt11 sequences indicates that a gene duplication occurred at the base of the vertebrate Wnt11 clade. The developmental expression domains of AmphiWnt11 resemble those of Wnt11 homologs in vertebrates. The earliest detectable expression is transiently associated with the dorsal lip of the blastopore. At the neurula stage, AmphiWnt11 is expressed in myotomal muscle cells; however, AmphiWnt11 transcription is not associated with metameric pre-patterning prior to morphological segmentation. Finally, in amphioxus and the vertebrates, Wnt11 homologs are expressed in anteroventral ectoderm and in association with the tailbud and the tail fin. Thus, in amphioxus and lower vertebrates, the posterior expression of Wnt11 may be involved in tail fin outgrowth, and this ancient genetic program might have been co-opted at least in part for lateral appendage development during vertebrate evolution. genesis 27:1-5, 2000.

Amino Acid Sequence↗