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Biomedical subjects

G Weber

Publications and source records attributed to G Weber.

At least 505 records · Page 28Linked to original sources
PubMed1984

Negative correlation of L-glutamine concentration with proliferation rate in rat hepatomas.

The concentration of L-glutamine was determined in freeze-clamped samples of normal liver of adult male fed rats (5.7-6.1 mumol/g) and in transplantable hepatomas of vastly different proliferative rates. The L-glutamine concentration in the slowly growing hepatomas was in the range of the normal liver and it decreased in relation to the increase of hepatoma growth rate, in the most rapidly growing tumors amounting to 12% of that of normal liver. In 24-hour regenerating liver, the glutamine content was slightly reduced (by 17%). In normal rat organs of high cell renewal, such as testis, intestinal mucosa, spleen, and thymus, the L-glutamine concentration was 18 to 46% of that of normal rat liver. The L-glutamine content was similar in rat brain and liver, but it was 1.6-fold higher in the heart, and low in the blood. Glutamine synthetase (EC 6.3. 1.3) activity in normal adult liver of ACI/N strain rats was 1,000 nmol per hr per mg protein; the activity increased in the very slowly growing hepatoma 20, but decreased markedly in all the other hepatomas. Thus, glutamine synthetase activity was essentially transformation-linked. The negative correlation of glutamine content with growth rate in transplanted hepatomas appears to be more closely linked with the activities of enzymes that utilize glutamine. The low L-glutamine concentration in the rapidly growing hepatomas provides a potential marker for anti-glutamine chemotherapy selectively targeted against the glutamine-utilizing enzymes.

Animals↗
PubMed1984

High cytotoxicity and membrane permeability of Et3Pb+ in mammalian and plant cells.

Cells of mammalian origin as well as those of higher plants appear to be very sensitive to triethyllead ion (Et3Pb+). Neuroblastoma cells kept in the presence of 1 microM Et3Pb+ lost their viability within 6 h. Growth of suspension culture cells of soybean (G. max(L.)Merr.) was inhibited by 1 microM Et3Pb+, and finally the cells died. Morphologically, Et3Pb+ caused the complete breakdown of microtubular structures in neuroblastoma cells; thus microtubules appeared to be the main target for the toxin. While in a previous study the effect of Et3Pb+ on microtubules has been well documented at concentrations of 50-200 microM 1, the present study demonstrates that the formation of microtubules from pig brain tubulin is disturbed at concentrations of Et3Pb+ as low as 0.5 to 1 microM. We conclude from these data that Et3Pb+ freely permeates the plasma membranes of mammalian as well as plant cells.

Animals↗
PubMed1984

Three-dimensional structure of fungal proteinase K reveals similarity to bacterial subtilisin.

The three-dimensional structure of the fungal serine protease proteinase K has been determined at 3.3 A resolution by single crystal X-ray diffraction analysis. The enzyme crystallizes in the tetragonal space group P4(3)2(1)2 with cell constants a = b = 68.3 A, c = 108.5 A. The asymmetric unit consists of one monomer of 27 000 daltons mol. wt., approximately 50% higher than the so far assumed value of 18 500 daltons. The main chain fold of proteinase K shows a high degree of tertiary homology with the corresponding bacterial subtilisin BPN'. Proteinase K is the second enzyme in this family of serine proteases to be studied by X-ray diffraction, thus confirming the existence of two unrelated families of serine proteases in pro-and eukaryotes.

Bacteria↗
PubMed1984

[Types of binding of iron, copper and zinc in various varieties of tea].

Extracts of several varieties of tea were separated by HPLC and the resulting substances detected by various techniques with a view to characterizing the fractions of organic metal complexes of copper, zinc, and iron. In addition to uv methods and conductivity measurements particular stress was laid on the application of HPLC coupled with chemical reaction detectors for metals (photometric determination of total content) and for functional groups, such as phenolic OH-, SH-, and NH-groups. The distribution of the different metals was found by coupling HPLC with AAS. The chromatograms obtained permitted the fractions of individual metals to be attributed to the appropriate organic binding forms. With tea, phenolic bonds are important but binding to amino groups could also be shown to exist. The differences between the types of metal binding forms encountered in the varieties of tea investigated are caused by their constituents and/or by their modification brought about by processing.

Amines↗
PubMed1984

Increased plasma and aortic triglycerides in rabbits after acute administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Administration of a single nonlethal dose (20 micrograms/kg) of 2,3,7,8-tetrachlorodibenzo-p-dioxin to New Zealand male rabbits, both on a standard and on a cholesterol (0.5% in the diet) regimen, resulted in a significant increase of plasma triglyceride levels. Triglycerides were particularly raised in the very low-density lipoprotein fraction; no significant apolipoprotein changes, as assessed by an analytical isoelectrofocusing procedure, could be determined. Concomitant to the increased triglyceridemia, aortic triglycerides were also significantly elevated in 2,3,7,8-tetrachlorodibenzo-p-dioxin-pretreated rabbits, both on the standard and on the cholesterolemic regimen. These findings suggest that 2,3,7,8-tetrachlorodibenzo-p-dioxin, possibly by inhibiting triglyceride breakdown, may induce an atherogenic form of hypertriglyceridemia in a standard experimental model of atherosclerosis.

Animals↗
PubMed1984

Control of enzymic programs and nucleotide pattern in cancer cells by acivicin and tiazofurin.

The mechanism of action of acivicin and tiazofurin was compared in hepatoma 3924A. The results were evaluated by assessing the impact of these drugs on primary targets, the activities of key enzymes, and on secondary and tertiary targets, the concentrations of pools of ribonucleotides and deoxyribonucleotides. The action of acivicin entails inhibition and inactivation of the key enzymes of glutamine utilization in the biosynthesis of purines and pyrimidines. As a result, the GTP and CTP pools were markedly depleted, whereas those of ATP and UTP were unaffected. Acivicin also markedly decreased the concentrations of all 4 deoxynucleoside triphosphates. The nucleotide pools returned to normal or near normal range within 2 to 3 days after a single acivicin injection. The pharmacologic targets of acivicin in anticancer chemotherapy include prominently the activities of glutamine-utilizing enzymes and the pools of GTP and CTP and all 4 dNTP's. These biochemical targets also serve as indicators of acivicin action in cancer cells. The action of tiazofurin in hepatoma cells entails the primary target, IMP dehydrogenase. The subsequent effects include marked enlargement of IMP and PRPP pools and depletion of the pools of GDP and GTP. The increased IMP concentration selectively inhibited the activities of hypoxanthine-guanine phosphoribosyltransferase, but did not affect that of adenine phosphoribosyltransferase. The markedly decreased GTP pool de-inhibited the activity of AMP deaminase which permitted the channeling of AMP to IMP. An important indicator of tiazofurin action is the prolonged depletion of dGTP pools and similar but less pronounced declines in the pools of dCTP and dATP. In contrast, dTTP pools were increased. The crucial biochemical targets and indicators of tiazofurin action in sensitive cancer cells include inhibition of IMP dehydrogenase, a decrease in the concentrations of GDP, GTP, dGTP, dCTP, dATP and marked rise in the pools of IMP, PRPP and dTTP. Measurements of the molecular targets and indicators of drug action should be helpful in identifying cancer cells and tissues sensitive or resistant to the action of acivicin or tiazofurin. Identification of the targets and indicators should also be helpful in the design of frequency of administration of the drugs in combatting animal and human neoplasia.

Animals↗
PubMed1984

Analogs of arachidonic acid methylated at C-7 and C-10 as inhibitors of leukotriene biosynthesis.

The syntheses and biological activity of (all Z)-7,7-dimethyl-5,8,11,14- eicosatetraenoic acid, (all Z)-7,7,-dimethyl-5,8,11-eicosatrienoic acid, (Z,Z)-7,7-dimethyl-5,8-eicosadienoic acid, (all Z)-10,10-dimethyl-5,8,11,14-eicosatetraenoic acid, (all Z)-10,10-dimethyl-5,8,11-eicosatrienoic acid, and rac.-(Z,Z)-15-hydroxy-7,7-dimethyl-5,8-eicosadienoic acid are described. These arachidonic acid analogs are all inhibitors of ionophore-induced SRS-A biosynthesis in rat peritoneal cells. Their mode of action may involve inhibition of phospholipase A2 rather than delta 5-lipoxygenase. These compounds failed to exhibit significant activity in an in vivo model designed to detect inhibitors of antigen-induced, leukotriene-mediated bronchoconstriction in sensitized guinea pigs.

Animals↗
PubMed1984

A model of dynamic quenching of fluorescence in globular proteins.

A model is presented for the quenching of a fluorophore in a protein interior. At low quencher concentration the quenching process is determined by the acquisition rate of quencher by the protein, the migration rate of quencher in the protein interior, and the exit rate of quencher from the protein. In cases where the fluorescence emission observed in the absence of quencher could be described by a single exponential decay, the presence of quencher led to doubly exponential decay times, and the aforementioned exit rates of the quencher could be determined from experimental data. At high quencher concentration, the processes became more complex, and the deterministic rate equations used at low quencher concentration had to be modified to take into account the Poisson distribution of quencher molecules throughout the protein ensemble and also by using a migration rate for quencher in the protein interior that is a function of the quencher concentration. Simulations performed for typical fluorescent probes in proteins showed good agreement with experiments.

Kinetics↗
PubMed1984

Oxygen distribution and migration within Mbdes Fe and Hbdes Fe. Multifrequency phase and modulation fluorometry study.

Quenching of the intensity and lifetime of porphyrin fluorescence from Mbdes Fe and Hbdes Fe (iron-free myoglobin and hemoglobin) by oxygen was investigated using a multifrequency cross-correlation phase fluorometer. The single exponential decay characteristic of porphyrin emission of Mbdes Fe and Hbdes Fe became doubly exponential upon application of oxygen pressure. The results were interpreted in terms of a general model of dynamic quenching of fluorescence in globular proteins. The model accounted for the rate k+ of acquisition of quencher by the protein, the exit rate k- of quencher from the protein, and the migration rate chi of quencher in the protein interior. The values of k+, k-, and chi were different for Mbdes Fe and Hbdes Fe. The addition of 40% sucrose, which increased the bulk viscosity sixfold, modified these rates. These results are discussed and compared with previous quenching studies on proteins. The significance of these results and the model for the interpretation of protein quenching studies is emphasized.

Animals↗
PubMed1984

Order of free energy couplings between ligand binding and protein subunit association in hemoglobin.

The number of protein subunits that must be liganded to effect changes in subunit interaction may be characterized by defining an order for the free energy couplings between these two processes. From available data on the chemical equilibrium of stripped hemoglobin A with oxygen, I show that couplings are unequivocally of first order. The two-state model of cooperative binding is shown to be incompatible with the results of this analysis, as the Monod-Wyman-Changeux parameters derived from the same experimental data demand free energy couplings of an order higher than the second.

Allosteric Regulation↗
PubMed1984

Increased 5-phospho-alpha-D-ribose-1-diphosphate synthetase (ribosephosphate pyrophosphokinase, EC 2.7.6.1) activity in rat hepatomas.

The behavior of the activity of 5-phosphoribosyl 1-pyrophosphate (PRPP) synthetase (ribosephosphate pyrophosphokinase, EC 2.7.6.1) was elucidated in normal rat liver, in 11 hepatomas of different growth rates, and in rapidly growing differentiating and regenerating liver. Tissue extracts were prepared by centrifugation of 10% homogenates at 100,000 X g for 30 min, and enzyme activity was measured in the protein fractions obtained by 40 and 47% ammonium sulfate saturation of the supernatant fluids from livers and hepatomas, respectively. In the tissue extracts, there was no interfering enzyme activity that utilized PRPP under the standard assay conditions. The affinity of PRPP synthetase for its substrates, ribose 5-phosphate and adenosine triphosphate (ATP), and to Mg2+ was similar in liver and hepatoma extracts. The Km for ribose 5-phosphate was 0.3 mM; for ATP, it was 0.1 mM in the presence of excess Mg2+. The Km for Mg2+ ATP was 1.2 mM in the presence of excess ATP. There was no difference in the affinity of the enzyme for its activators, Mg2+ and inorganic phosphate, in liver and hepatoma preparations; the Km for Mg2+ was 0.6 mM in the presence of excess ATP; the Km for inorganic phosphate was 14.0 mM. The requirement of hepatoma extracts for full phosphate saturation was higher than that of liver extracts (85 versus 65 mM). A standard assay was worked out for the liver and hepatoma systems; in liver, the enzyme activity was linear for 30 min incubation, and in hepatoma it was linear for 15 min incubation. PRPP synthetase activity was proportionate with amounts of protein added over a range of 0.4 to 3.0 mg in both liver and hepatoma extracts. In the liver of normal adult Wistar rats, PRPP synthetase activity was 108 +/- 10 nmol/hr/mg protein. In rat tissues of high cell renewal activity, thymus, testis, spleen, and small intestine, synthetase specific activity was 3.7-, 3.6-, 1.2-, and 1.3-fold higher than that of normal liver. The synthetase specific activity in hepatomas of slow growth rate increased 1.2- to 1.5-fold, and in intermediate and rapidly growing hepatomas it was elevated 1.9- to 4.1-fold higher than that of normal liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1984

Enzymic capacities of purine de Novo and salvage pathways for nucleotide synthesis in normal and neoplastic tissues.

The enzymic capacities of the de novo and the salvage pathways for purine nucleotide synthesis were compared in rat in normal, differentiating, and regenerating liver, and in three hepatomas of widely different growth rates. The activities of the key de novo and salvage enzymes were also determined in mouse lung and Lewis lung carcinoma, in human kidney and liver, and in renal cell carcinoma and hepatocellular carcinomas. A precise and reproducible assay was worked out for measuring the activities of adenine phosphoribosyltransferase (EC 2.4.2.7) and hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8) in crude liver and hepatoma systems. Kinetic studies on the salvage enzymes were carried out in the crude 100,000 X g supernatant fluid from normal liver and rapidly growing hepatoma 3924A. In both tissue extracts, Michaelis-Menten kinetics was observed for adenine phosphoribosyltransferase and HGPRT. The reciprocal plots for 5-phosphoribosyl-1-pyrophosphate (PRPP) of liver and hepatoma enzymes gave apparent KmS of 2 microM for adenine phosphoribosyltransferase and 4 microM for HGPRT, showing two orders of magnitude higher affinities for PRPP than that of the rate-limiting enzyme of de novo purine synthesis, amidophosphoribosyltransferase (EC 2.4.2.14) (Km = 400 to 900 microM). The apparent Km values for adenine of liver and hepatoma adenine phosphoribosyltransferase were 0.6 to 0.9 microM, respectively. For both liver and hepatoma HGPRT, the reciprocal plots for hypoxanthine and guanine yielded the same Km of 3 microM. The specific activities of purine phosphoribosyltransferases were markedly higher than that of amidophosphoribosyltransferase in rat thymus, spleen, testis, bone marrow, colon, liver, kidney cortex, lung, heart, brain, and skeletal muscle, but were lower in the small intestine. In hepatomas and regenerating and differentiating liver, the activities of the salvage enzymes were 2.1- to 32-fold higher than that of amidophosphoribosyltransferase. The purine phosphoribosyltransferase activities were also higher than that of amidophosphoribosyltransferase in Lewis lung carcinoma (8.2- to 32-fold), human renal cell carcinoma (3.5- to 22-fold), and hepatocellular carcinoma (3.4- to 30-fold). The high activities and the high affinity to PRPP of the purine phosphoribosyltransferases might explain the lack of linkage of the behavior of these enzymic activities with proliferation in normal, regenerating, differentiating, or neoplastic tissues. In contrast, the specific activity of the amidophosphoribosyltransferase, which is lower than that of the salvage enzymes, is linked with transformation as it is increased in all examined tumors.4

Adenine Phosphoribosyltransferase↗
PubMed1984

Evaluation of the slide agglutination test for detection of leptospiral antibodies in serum samples of slaughter pigs.

Serum samples of 259 randomly selected slaughter pigs were studied comparatively in the microscopic agglutination test (MAT) and the slide agglutination test (SAT) for the presence of leptospiral antibodies. 12 of 13 serum samples with MAT titres of 1:400+ + and higher were positive in the SAT. 27 of 46 sera with MAT titres in the borderline range (1:100+ + to 1:400+) showed a positive reaction in the SAT. 31 of 200 serum samples with MAT titres of 1:100+ and less reacted also positively in the SAT. Statistical evaluation of the results showed that the SAT is accurate if results are positive but less so if the results are negative (sensitivity 92.3%, specificity 76.4%).

Abattoirs↗