PubMed Health⌕ Search

Biomedical subjects

J Feuerstein

Publications and source records attributed to J Feuerstein.

At least 19 recordsLinked to original sources
PubMed1992

Economic aspects of therapeutic drug monitoring.

In the last two decades two major trends heavily influenced the situation of the clinical laboratories. Cost saving issues have become more and more significant and an exploding number of tests has to be performed by a limited number of technicians. The latter task is facilitated by the use of automated analyzers. The CEDIA assays for therapeutic drug monitoring (TDM) can be performed on Boehringer Mannheim/Hitachi systems used for routine clinical chemistry. This means that now it is possible to determine all parameters of clinical chemistry, proteins, and TDM without sample splitting on one analyzer, resulting in saving of manual workload and costs.

Cost-Benefit Analysis↗
PubMed1990

Kinetics of interaction of nucleotides with nucleotide-free H-ras p21.

A method is described for the convenient preparation of substantial quantities of nucleotide-free p21 or of 1:1 complexes with nucleotides other than GDP. The nucleotide-free protein has been used for kinetic studies of the binding of GDP and GTP, making use of the fluorescent analogues 3'-(methylanthraniloyl)-2'-deoxy-GDP and -GTP. Stopped-flow studies have led to the formulation of a two-step binding mechanism for both GDP and GTP, involving initial rapid but weak binding of the nucleotide followed by a relatively slow (10-20 s-1 at 25 degrees C; 3-5 s-1 at 5 degrees C) quasi-irreversible isomerization reaction. By use of a nonequilibrium competition method, guanosine and GMP have been shown to interact weakly but significantly with p21 (dissociation constants of 153 and 29 microM, respectively). The presence of guanosine or GMP at the active site of p21 leads to a marked stabilization of p21 against spontaneous denaturation when compared with the nucleotide- and nucleoside-free protein.

Guanosine↗
PubMed1990

Stereochemistry and lifetime of the GTP hydrolysis intermediate at the active site of elongation factor Tu from Bacillus stearothermophilus as inferred from the 17O-55Mn superhyperfine interaction.

Electron paramagnetic resonance spectroscopy has been used to obtain information on the structure and stability of the products of GTP cleavage at the active site of elongation factor Tu (EF-Tu) from Bacillus stearothermophilus. Using stereospecifically labelled (Sp)-(Rp)-[beta-17O]GTP (prepared by modification of a previously published procedure which is now also suitable for guanine nucleotides), it was found that only one of the two possible diastereomers (Sp) led to detectable line-broadening of the EPR spectrum of Mn2+ at the active site of EF-Tu (linewidth 1.5 mT), whereas the Rp isomer caused the same linewidth as unlabelled nucleotide (1.3 mT). From our earlier work and from a demonstration that the lifetime of the state giving the broadened spectrum is too long to be assigned to the EF-Tu.GDP.Mn complex [the rate constant for decay as measured by displacement of GDP by the fluorescent 2'(3')-O-(N-methylanthraniloyl)-GDP is 6.2 x 10(-3) s-1 at 25 degrees C and pH 6.8], we conclude that the broadened signal arises from the EF-Tu.Mn.GDP.Pi complex, the predominant steady-state species. During the hydrolysis of GTP the Mn2+ remains bound to the beta-phosphate oxygen of GDP which arises from the beta pro-S oxygen of GTP, possibly until GDP dissociates and certainly until Pi dissociates. Addition of elongation factor Ts (EF-Ts) to this intermediate leads to rapid reduction of the linewidth to that expected for random distribution of interactions of one 17O and two 16O atoms of GDP with Mn2+, and is not distinguishable from that exhibited by (Rp)-[beta-17O]GTP in the corresponding complex in the presence of EF-Ts.

Binding Sites↗
PubMed1989

The mechanism of guanosine nucleotide hydrolysis by p21 c-Ha-ras. The stereochemical course of the GTPase reaction.

The use of guanosine 5'-O-(gamma-thio)triphosphate as a substrate for p21 c-Ha-ras was established. By using chirally labeled [gamma-17O,18O]guanosine 5'-O-(gamma-thio)triphosphate, the stereochemical course of the GTPase reaction was determined. The analysis shows that the hydrolysis occurs with inversion at the gamma-phosphorus. This shows that the most likely mechanism is a single step, in-line transfer, without a phosphoenzyme or other phosphorylated intermediate.

Adenosine Triphosphate↗
PubMed1988

Spectroscopic and hydrodynamic studies reveal structural differences in normal and transforming H-ras gene products.

We have recorded the circular dichroism spectra of the cellular and the viral H-ras gene products both in the absence and in the presence of guanine nucleotides and analyzed these spectra in terms of the secondary structure composition of these proteins. It is shown that the GTP complex of the ras proteins has a different secondary structure composition than the GDP complex and, furthermore, that there are differences in the secondary structure of the viral ras protein and the cellular ras protein. We have also recorded and analyzed the circular dichroism spectrum of the isolated guanine nucleotide binding domain of the Escherichia coli elongation factor Tu (EF-Tu), which has been considered as a model for the tertiary structure of the ras proteins [McCormick, F., Clark, B. F. C., LaCour, T. F. M., Kjeldgaard, M., Norskov-Lauritsen, L., & Nyborg, J. (1985) Science (Washington, D.C.) 230, 78-82]. Our data show that the guanine nucleotide binding domain of EF-Tu (30% alpha-helix and 16% beta-pleated sheet for the GDP complex) has quite a different secondary structure composition than the ras proteins (e.g., the cellular ras protein has 47% alpha-helix and 22% beta-pleated sheet for the GDP complex), indicating that the protein core comprising the guanine nucleotide binding site might be similar but that major structural differences must exist at the portion outside this core. Normal and transforming ras proteins also differ slightly in their hydrodynamic properties as shown by sedimentation velocity runs in the analytical ultracentrifuge.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Transformation, Neoplastic↗
PubMed1987

Preparation and characterization of nucleotide-free and metal ion-free p21 "apoprotein".

p21 isolated under nondenaturing conditions is obtained as a complex with guanosine nucleotides and magnesium ions. We have developed a high performance liquid chromatography method which removes greater than 95% of bound nucleotide and the metal ion very rapidly under mild conditions. At the same time, p21 is purified from minor protein impurities. The protein thus prepared is thermally much less stable than the complexed p21, but can be used for studying its interaction with nucleotides and metal ions at low temperatures. The association rate constant for p21 and GDP is 1.47 X 10(6) M-1 s-1 and for GTP is 2.9 X 10(6) M-1 s-1 at 0 degree C. By using appropriately determined dissociation rate constants we have determined the binding constant for p21.GDP and p21.GTP in the presence of excess Mg2+ to be 5.7 X 10(10) M-1 and 6.0 X 10(10) M-1, respectively, at 0 degree C.

Guanine Nucleotides↗
PubMed1987

Characterisation of the metal-ion-GDP complex at the active sites of transforming and nontransforming p21 proteins by observation of the 17O-Mn superhyperfine coupling and by kinetic methods.

Kinetic studies on the interaction of three Ha-ras-encoded p21 proteins with GDP and MgGDP have yielded values for the association (10(6)-10(7) M-1 s-1) and dissociation (10(-3)-10(-5) s-1) rate constants at 0 degrees C. Dramatic differences in the rate constants were not observed for the three proteins. Under non-physiological conditions (absence of Mg2+), the rate constant for GDP release was an order of magnitude faster for the viral protein p21v than for the cellular form p21c or the T24 mutant p21t, but this was reduced to a factor of about 3 in the presence of Mg2+. In all cases, there was an increase of about one order of magnitude in the rate of GDP release on removing magnesium. The binding affinities ranged from 5.7 X 10(10) M-1 for p21c to 1.3 X 10(11) M-1 for p21v. Electron paramagnetic resonance (EPR) measurements on Mn2+ bound together with stereospecifically 17O-labelled GDP showed direct coordination of a beta-phosphate oxygen to the metal ion with a superhyperfine coupling constant of 0.16-0.22 mT, but no interaction with the alpha-phosphate oxygens at the active site of all three proteins. The association constant of Mn(II) to p21 proteins in the absence of nucleotides was estimated to be greater than 10(5) M-1. In agreement with the EPR results, experiments on the metal ion dependence of the binding of thiophosphate analogs of GDP provided further evidence for the absence of direct coordination of the metal ion to the alpha-phosphate group. These results have been used to construct a model for the interactions of Mg X GDP with the active site of p21 proteins.

Binding Sites↗
PubMed1986

Expression of p21 proteins in Escherichia coli and stereochemistry of the nucleotide-binding site.

v-Ha-ras encoded p21 protein (p21V), the cellular c-Ha-ras encoded protein (p21C) and its T24 mutant form p21T were produced in Escherichia coli under the control of the tac promoter. Large amounts of the authentic proteins in a soluble form can be extracted and purified without the use of denaturants or detergents. All three proteins are highly active in GDP binding, GTPase and, for p21V, autokinase activity. Inhibition of [3H]GDP binding to p21C by regio- and stereospecific phosphorothioate analogs of GDP and GTP was investigated to obtain a measure of the relative affinities of the three diphosphate and five triphosphate analogs of guanosine. p21 has a preference for the Sp isomers of GDP alpha S and GTP alpha S. It has low specificity for the Sp isomer of GTP beta S. Together with the data for GDP beta S and GTP gamma S these results are compared with those obtained for elongation factor (EF)Tu and transducin. This has enabled us to probe the structural relatedness of these proteins. We conclude that p21 seems to be more closely related to EF-Tu than to transducin.

Cell Line↗
PubMed1984

[Diagnosis of moderate stenoses of the origin of the internal carotid artery using the continuous emission Doppler technic: semeiologic study].

The authors propose two signs for detecting moderate (about 50% reduction of the arterial lumen) stenosis at the origin of the internal carotid (IC) using the Doppler technique: (1) the 'arch-pattern,' drawn on the systolic and diastolic blood flow velocity enveloping curve when slowly translating the probe from the common carotid (CC) to the end of the accessible part of the IC; (2) The 'proximo-distal carotidian ratio,' the latter being pathological if below 1. A large scale confrontation with angiography is still necessary to validate them.

Carotid Artery Diseases↗
PubMed1983

[Monotherapy with sodium valproate in generalized primary epilepsy. 2d phase: Study of long-term efficacy and tolerance].

From the analysis of 115 cases of primary generalized epilepsies treated for a mean duration of 43 months with sodium valproate as sole therapy, it appears that: the mean effective daily dosage is 21 mg/kg; the efficacy of valproate proved excellent in 82.6% of cases (seizures fully controlled: 74%, seizures occurring exceptionally: 9%); a loss of activity was never observed; in these circumstances of prolonged administration of the drug, no signs of major intolerance were seen; side-effects occurred in 29% of cases, including 20% long-term effects (weight gain, essential tremor); 64 series of laboratory tests including 15 parameters made it possible to evaluate the hematological, hepatic and pancreatic tolerance of valproate: the majority of the tests were normal. The authors believe that during long-term therapy with valproate, monitoring does not need to include the routine performance of liver function tests, but that it would be more advisable, should a suggestive clinical sign be noted, to investigate the platelet count, coagulation (partial activated thromboplastin time) and protein synthesis (fibrinogen).

Adult↗
PubMed1983

[Apropos of a case of thyrotoxic periodic paralysis (TPP): electromyographic study (EMG)].

The authors report on a case of thyrotoxic periodic paralysis characterized by attacks of flaccid tetraplegia with hypokalemia in a patient with Basedow disease, the cure of which led to the disappearance of the neurological symptomatology. The EMG investigations, performed in the course of a spontaneous paralytic attack, showed the same abnormalities as in the few similar published cases: discordance between the rich interferential recordings and the weakness of the movements; low amplitude of the electrodetection tracings; reduced amplitude of the evoked muscle action potentials on nerve stimulation. These myogenic patterns are related to the aspect of the muscle biopsy which, when performed during the paralytic phase, shows a vacuolization of the muscular fibers. The pathophysiological underlying mechanisms of the thyrotoxic periodic paralysis still remain hypothetic.

Adult↗
PubMed1982

[A case of unilateral and lesional mu rhythm--clinical and encephalographic development].

One case of a strictly unilateral left rolandic mu rhythm, revealing a metastatic tumor of the concerned region, is reported. The clinical feature consisted of partial Jacksonian motor seizures involving the upper limb and the face on the right side. As the tumoral process extended, the mu rhythm turned into a 6 c/sec theta rhythm, similarly located and reactive, then into a larger and more active slow focus. This focus transistorily decreased under X-ray treatment. The particular aspects of this observation are discussed in the light of the literature data.

Aged↗
PubMed1981

[Frequency and semeiological evolution of epileptic seizures occurring between 40 and 65 years of age (author's transl)].

458 patients who had their first epileptic fit between the ages of 40 and 65 are classified into 5 groups according to the seizure symptomatology: when the symptomatology remains unchanged, the frequency of fits is less than 1 per month in 84% of generalized fits and more than 1 per month in 52% of focal fits. When the symptomatology changes, the frequency of fits is less than 1 per month when the inaugural fit is generalized (23 out of 27) and more than 1 per month when the inaugural fit is focal (15 out of 21). Modifications of the symptomatology correlate positively with a prevalence of tumor aetiology. Primary generalized epilepsies are rare (4.4%). Non-specific secondary generalized epilepsies (including vascular, metabolic or toxic encephalopathies) account for 24.4% of the cases. Focal epilepsies are the most common form (40.7%), elementary fits being four times more frequent than complex fits.

Adult↗
PubMed1980

Effect of phenformin on the metabolism of glucose, pyruvate and acetate in guinea-pig heart.

In the isolated perfused heart of the guinea-pig, phenformin could be shown to have a characteristic effect on cardiac performance and metabolism. In the working heart, phenformin (1 mmol1/1) decreased dp/dt and increased the end diatolic pressure; this reduced heart performance could not be explained by changes in the content of energy-rich compounds. Furthermore, phenformin increased lactate production in hearts perfused with glucose as substrate and inhibited the utilisation of pyruvate, but not of acetate. The activity of the purified pyruvate dehydrogenase complex was not influenced by phenformin, but the active form of the pyruvate dehydrogenase complex (PDHa) was diminished. This effect may be explained by an inhibition of the pyruvate dehydrogenase phosphatase. An inhibition of pyruvate dehydrogenase and, coincidently, of oxygen consumption might contribute to the development of lactic acidoses and, particularly, might be deleterious for the heart.

Adenine Nucleotides↗