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W Block

Publications and source records attributed to W Block.

At least 73 records · Page 4Linked to original sources
PubMed1983

The elongation factor Tu from Escherichia coli, aminoacyl-tRNA, and guanosine tetraphosphate form a ternary complex which is bound by programmed ribosomes.

The interaction of the Escherichia coli elongation factor Tu guanosine tetraphosphate complex (EF-Tu ppGpp) with aminoacyl-tRNAs(aa-tRNA) was reinvestigated by gel filtration and hydrolysis protection experiments. These experiments show that EF-Tu X ppGpp like EF-Tu X GDP (Pingoud, A., Block, W., Wittinghofer, A., Wolf, H. & Fischer, E. (1982) J. Biol. Chem. 257, 11261-11267) forms a fairly stable complex with Phe-tRNAPhe, KAss being 0.6 X 10(5) M-1 at 25 degrees C. The binding of the EF-Tu X ppGpp X aa-tRNA complex to programmed ribosomes was investigated by a centrifugation technique. It is shown that this complex is bound codon-specific with KAss = 3 X 10(7) M-1 at 0 degrees C and that it stimulates peptidyl transfer. A numerical estimation of the intracellular concentration of EF-Tu X GTP X aa-tRNA and EF-Tu X ppGpp X aa-tRNA during normal growth and under the stringent response indicates that ppGpp accumulation does affect the EF-Tu X GTP X aa-tRNA concentration but does not lead to major depletion of this pool. Furthermore, due to the higher affinity of EF-Tu X GTP to aa-tRNA and of the ternary complex EF-Tu X GTP X aa-tRNA to the ribosome, EF-Tu X ppGpp X aa-tRNA binding to the ribosome is not significant. According to our measurements and calculations, therefore, a direct participation of EF-Tu in slowing down the rate of protein biosynthesis and improving its accuracy during amino acid starvation is not obvious.

Escherichia coli↗
PubMed1982

The elongation factor Tu binds aminoacyl-tRNA in the presence of GDP.

Escherichia coli elongation factor (EF-Tu) binds aminoacyl-tRNAs (aa-tRNA) not only in the presence of GTP but also in the presence of GDP. Complex formation leads to a protection of the aa-tRNA against nonenzymatic deacylation and digestion by pancreatic ribonuclease, as well as to a protection of EF-Tu against proteolysis by trypsin. The equilibrium constant for the binding of Phe-tRNAPheyeast for example to EF-Tu.GDP has been determined to be 0.7 X 10(5) M-1 which is 2 orders of magnitude lower than the equilibrium constant for Phe-tRNAPheyeast binding to EF-Tu.GTP. In the presence of kirromycin, aminoacyl-tRNA binding to EF-Tu.GDP is not affected as much: Phe-tRNAPheyeast is bound with an equilibrium constant of 3 X 10(5) M-1. While there is also a measurable interaction between EF-Tu.GTP and tRNA, such an interaction cannot be detected with EF-Tu.GDP and tRNA, not even at millimolar concentrations. A so far undetected complex formation between aminoacyl-tRNA and EF-Tu.GTP in the presence of pulvomycin, however, could be detected. The results are discussed in terms of the structural requirements of ternary complex formation and in the light of proofreading schemes involving A-site binding on the E. coli ribosome.

Escherichia coli↗
PubMed1982

The antibiotics kirromycin and pulvomycin bind to different sites on the elongation factor Tu from Escherichia coli.

Pulvomycin and kirromycin, two antibiotics which inhibit protein biosynthesis in Escherichia coli by complex formation with the elongation factor Tu (EF-Tu), bind to different sites on the protein. While only one molecule of kirromycin can be bound to one molecule of EF-Tu, more than one molecule of pulvomycin interacts with a molecule of EF-Tu. This has been deduced from experiments in which the aminoacyl-tRNA binding and the GTPase activity of EF-Tu were measured in the presence of varying amounts of both antibiotics. These experiments are interpreted to mean that pulvomycin but not kirromycin can replace the other antibiotic in its respective site. Our conclusions are supported by circular dichroism spectroscopy.

Aminoglycosides↗
PubMed1981

The elongation factor Tu . guanosine tetraphosphate complex.

The elongation factor Tu (EF-Tu) isolated from Escherichia coli cells that have undergone the stringent response is predominantly complexed with guanosine 5'-diphosphate 3'-diphosphate. This complex can be separated by anion-exchange chromatography from Ef-Tu . GDP. Unlike EF-Tu complexed with guanosine 5'-triphosphate 3'-diphosphate, the complex with guanosine 5'-diphosphate 3'-diphosphate cannot form a ternary complex with aminoacyl-tRNAs as can be shown directly by hydrolysis protection experiments.

Bacterial Proteins↗
PubMed1981

The pharmacokinetics, bioequivalence and bioavailability of different formulations of metoclopramide in man.

The pharmacokinetics of 4-amino-5-chloro-N-(2-diethylaminoethyl)-2-methoxybenzamide (metoclopramide, Paspertin) after a single dose of the drug in five different dosage forms: ampoules, tablets, drops, dragées and suppositories, were studied. The clinical investigations were carried out on 10 healthy subjects under carefully controlled conditions. The analysis of metoclopramide in plasma was carried out using reverse-phase high-pressure liquid chromatography. Bioavailabilities between 76 and 79% were determined for the oral application forms and 53% for the rectal application form. Significant differences between maximum plasma levels were found for different individuals. The initial distribution of the drug is very rapid, and the elimination half-lives are comparable for all formulations and ranged from 3.9 and 5.3 h. The apparent volume of distribution is 3.1 l/kg body weight and the total body clearance is 38.4 l/h.

Adolescent↗
PubMed1978

Chromatographic study on the specificity of bis-p-nitrophenylphosphate in vivo. Identification of labelled proteins of rat liver after intravenous injection of bis-p-nitro[14C]phenylphosphate as carboxylesterases and amidases.

The procedure established to isolate the carboxylesterases E1, E2 and EA from rat liver (Arndt, R. and Krisch, K. (1972) Hoppe-Seyler's Z. Physiol. Chem. 353, 589-598) was applied to characterize in vivo bis-p-nitro[14C]-phenyl-P-labelled proteins. The peaks of radioactivity and of residual enzyme activities (hydrolysing methylbutyrate, p-nitrophenylacetate and acetanilide) were found in the same peaks after column chromatography and could be related to the well-defined esterases E1, E2 and EA. There is no indication of a nonspecific binding of bis-p-nitrophenyl-P or of one of its metabolites. The relative quantitative amounts of E1, E2 and EA were calculated to represent 40, 14 and 46%, respectively, of the total carboxylesterase content of rat liver. The relative amount of bound (not dialysable) radioactivity in rat liver depended on the survival time. During purification, the yield of enzyme activities corresponded to that of bound radioactivity, confirming the specificity of bis-p-nitrophenyl-P in vivo. Hence the radioactive metabolites of the inhibitor obviously do not possess binding affinities of quantitative importance to the rat liver proteins.

Amidohydrolases↗
PubMed1977

Glucose tolerance and physical fitness: an epidemiologic study in an entire community.

A modification of the Harvard Step Test was administered to approximately 4700 males and females, age 10-69 in Tecumseh, Michigan. Heart rate response to this standardized exercise test is an estimate of capacity for muscular work. A blood sample was drawn 1 h after a glucose challenge on the same day the exercise test was given. Four skinfolds were measured as an index of body fatnes. It was the purpose of this analysis to study the relationship of glucose tolerance to heart rate response to exercise. All analyses were done in age and sex-specific sub-groups. The correlation coefficients are low but positive in all but one sub-group and half of the coefficients are statistically significant. This suggests that poor fitness for work (high heart rate in response to exercise) was related, albeit weakly, to lowered glucose tolerance. However, there is a positive relationship between body fatness on the one hand and serum glucose and heart rate response to exercise on the other. When the effect of body fatness was eliminated the relationship of heart rate response to exercise ahd glucose tolerance remained about the same; low but statistically significant in some age groups.

Adolescent↗
PubMedDate not supplied

Enhancement efficacy of magnetic starch microshperes (MSM) in conventional spin-echo and turbo spin-echo sequences at 0.5 T and 1.5 T.

The efficacy of the superparamagnetic contrast agent magnetic starch microspheres (MSM) was evaluated in vitro by NMR relaxometry and in vivo by MR imaging using T2-weighted spin-echo (SE) and turbo spin-echo (TSE) sequences at 0.5 T and 1.5 T in 60 normal rats who received MSM in doses of 10-50 mu mol/kg. MR imaging was performed using T2-weighted SE and TSE sequences. The relaxation rates 1/T1 and 1/T2 for liver and spleen increased linearly with MSM concentrations up to 30 mu mol/kg body weight, and approached almost constant levels for higher doses. The slopes in the linear part of the 1/T2 diagram were 0.62 Hz +/- 0.03 for the liver and 0.51 Hz +/- 0.06 x kg/mu mol for the spleen. On all T2-weighted sequences at 0.5 T and 1.5 T, liver signal-to-noise ratio (SNR) decreased by a factor of 2-3 already at the lowest dose of 10 mu mol/kg. SNR values of TSE sequences exceeded values for SE sequences by 50-80%. The SNR decrease was not significantly different between SE and TSE sequences. Our results show that MSM is well suited as a T2 contrast agent at both magnetic field strengths when using conventional SE and fast TSE sequences.

Animals↗
PubMedDate not supplied

Determination of 1H relaxation times of water in human bone marrow by fat-suppressed turbo spin echo in comparison to MR spectroscopic methods.

Relaxation times of water were measured in human vertebral bodies by a fat-suppressed dual-echo turbo spin echo/turbo inversion recovery MRI sequence. Comparison was made with T1 and T2 values obtained by localized 1H-MR spectroscopy. The accuracy of the results and the diagnostic potential of the fast quantitative MRI technique were evaluated in 20 volunteers, 11 patients with osteoporosis, 6 patients with lymphoma, and 6 patients with bone marrow metastasis. No significant alterations of T1 and T2 relaxation times of water and fat were found in osteoporosis. With both methods, an increase in the T1 values of the water resonance by 16% was observed in lymphomas, which was highly significant (P < .001) in the MRS measurements, and an elevation by the same amount was obtained by the MRI sequence for the metastases (P = .040). A strong reduction of fat fraction was quantified by MRS in the tumorous cases. T2 of the water resonance increased by more than 30% (P < .003) in metastases. Water T2 values obtained by the MRI sequence showed systematic deviations from the MRS results, especially at short echo spacings.

Adipose Tissue↗
PubMedDate not supplied

Magnetic resonance spectroscopic and relaxometric determination of bone marrow changes in anorexia nervosa.

OBJECTIVE: The objective of this study was to assess and quantify bone marrow changes in patients with anorexia nervosa using 1H magnetic resonance spectroscopy and relaxometry. METHODS: The bone marrow fat fraction and the longitudinal and transverse relaxation times (T1 and T2, respectively) of water were measured in the lumbar and femoral marrow of 20 patients with anorexia nervosa and 19 healthy control subjects. RESULTS: Patients with anorexia nervosa showed significant hyperhydration and reduction of the fat fraction in their bone marrow, predominantly in the proximal femur. These changes were associated with hematological abnormalities. In a retest of seven patients after psychotherapy and gain of weight, the pathological changes in marrow proved to be largely reversible in correlation with the increase in body mass index. CONCLUSIONS: Fat depletion and excess of tissue water in the bone marrow in anorexia nervosa can be quantified by 1H magnetic resonance spectroscopy and relaxometry. The distribution of the pathological changes in the lumbar and femoral marrow follows the pattern of normal bone marrow conversion from hematopoietic to cellular during childhood.

Adolescent↗
PubMedDate not supplied

Profiling cryopreservation protocols for Ribes ciliatum using differential scanning calorimetry.

DSC analysis was performed at three points in the cryopreservation process on encapsulated-dehydrated meristems of Ribes ciliatum. Meristems were excised from shoots pre-treated with either sucrose or glucose, encapsulated in alginate beads, dehydrated in sucrose solutions, air dried, and plunged in liquid nitrogen. Thermal analysis revealed glass transitions during cooling of air-desiccated meristems, however, on rewarming a small endothermic event was detected suggesting glass destabilization can occur. Interestingly, this did not occur in alginate beads or meristems when these components were cooled and rewarmed separately. The possibility exists that thermal and moisture gradients may arise within the alginate bead/tissue complex and we propose that the heterogeneous composition of the meristems and the surrounding alginate may promote ice nucleation on rewarming. The significance of this regarding the stabilization of glasses formed in alginate beads and their encapsulated meristems is discussed. This study also reports an approach to Ribes cryopreservation in which the pregrowth of shoots in 0.75M sucrose for 1 week can be used as a substitute for cold acclimation.

Journal Article↗