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G Weber

Publications and source records attributed to G Weber.

At least 451 records · Page 25Linked to original sources
PubMed1986

Dissociation of the lactose repressor protein tetramer using high hydrostatic pressure.

Dissociation of lac repressor tetramer by high hydrostatic pressures was monitored with intrinsic tryptophan fluorescence. With the assumption of complete dissociation to monomer, tryptophan polarization data gave delta V a approximately 170 mL/mol and the concentration for 50% tetramer dissociation, C1/2, was 3.8 X 10(-8) M. Upon addition of inducer, the calculated delta V a increased to approximately 220 mL/mol and the C1/2 decreased to approximately 1 X 10(-8) M, a free energy difference of approximately 0.7 kcal. These results indicate a modest stabilization of the tetramer by the presence of inducer. Monitoring the average energy of tryptophan emission demonstrated that tetramer dissociation takes place over the same range of pressures as evidenced by the polarization data and IPTG dissociation can be more or less superimposed upon tetramer dissociation depending upon the ligand concentration used. Although the two transitions cannot be separated entirely, the delta V a for the region of the pressure dependence dominated by ligand dissociation was 69 mL/mol, an unexpectedly large value. For tetramer modified with methyl methanethiosulfonate, subunit dissociation was shifted to much higher pressures and IPTG dissociation did not occur. The delta V a for subunit association was calculated as approximately 160 mL/mol, and the C1/2 was 3.5 X 10(-9) M. Interactions at the subunit interface of the modified protein are apparently stronger than in the unmodified protein. The absence of inducer dissociation from the MMTS-modified tetramer by the application of high hydrostatic pressure suggests that the volume change for inducer binding to the modified protein is much smaller than that observed for the unmodified repressor.

Escherichia coli↗
PubMed1986

Amphotericin B renders stationary phase hepatoma cells sensitive to dipyridamole.

This study provides evidence that the dipyridamole inhibitory effect on nucleoside incorporation changed with culture time. Lag and log phase hepatoma 3924A cells were highly sensitive to dipyridamole with IC50 values for thymidine incorporation of 0.20 and 0.31 microM, respectively. In contrast, stationary phase cells were comparatively insensitive to dipyridamole with an IC50 of 38.9 microM. Amphotericin B (10 microM) restored the sensitivity of stationary phase cells to dipyridamole, lowering the IC50 value for thymidine incorporation to 0.25 microM. Amphotericin B also enhanced the cytotoxicity of dipyridamole to hepatoma 3924A cells. The combination of amphotericin B and dipyridamole may be useful in cancer chemotherapy.

Amphotericin B↗
PubMed1986

[Treatment of psoriasis arthropathica with bromocriptine].

35 patients suffering from psoriatic arthritis were systemically treated with bromocriptine at increasing doses, starting at 2.5 mg up to 30 mg per day. In 77% of the patients, we observed significant remission; 34% showed total remission and 43% remission of approximately 50% of the articular symptoms. Previous long-term treatment with commonly used anti-rheumatic drugs was not effective in any of the cases.

Adult↗
PubMed1986

Pressure dissociation and conformational drift of the beta dimer of tryptophan synthase.

Micromolar solutions of tryptophan synthase beta 2 dimer dissociate into monomers in the pressure range of 800-1600 bars as shown by studies of the spectral shift of the intrinsic fluorescence and of the fluorescence polarization of dansyl conjugates. At 25 degrees C the standard change in volume on dissociation (dV0) of the holoprotein was -162 mL mol-1, and the dissociation constant at 1 bar was K0 = 3.7 10(-10) M. Pyridoxal-reduced holoprotein and apoprotein had, within 10%, the same dV0, but K0 was decreased in the reduced protein (6 X 10(-11) M) and increased in the apoprotein (3.6 X 10(-9) M). At 4 degrees C the free energy of association of the holoprotein was reduced by 1.4 kcal mol-1, but dV0 was unchanged. In all the protein forms the decompression curves differed from the respective compression curves, indicating the loss of some free energy of association following separation of the monomers. This hysteretic behavior was largest in the apoprotein and amounted to a loss of 2.6 kcal mol-1 in the free energy of association. When the pressure was rapidly raised to 2.2 kbars, half-dissociation of the reduced pyridoxal beta 2 dimer took approximately 12 min. Upon return to atmospheric pressure reassociation was complete in 2-3 min and half of the enzyme activity was regained in 10 min; pyridoxal fluorescence recovered more slowly with a biphasic course. The independent return of these properties and the hysteretic behavior indicate that subunit separation is followed by a conformational drift like that observed in lactate dehydrogenase dissociated by either pressure or temperature or in enolase dissociated by dilution.

Escherichia coli↗
PubMed1986

Pressure-induced dissociation of solubilized sarcoplasmic reticulum ATPase.

The effect of hydrostatic pressure on the self-association of sarcoplasmic reticulum ATPase solubilized by nonionic detergent was studied in the pressure range of 1 atm up to 2 kilobars. Polarization of intrinsic tryptophan fluorescence or of fluorescence of a pyrene probe covalently attached to the ATPase was measured. An increase in hydrostatic pressure promoted dissociation of the protein into monomers. For a midpoint dissociation pressure of 1.3 kilobars, the standard volume change in the dissociation reaction was delta Vop = -167 ml/mol. Full reversibility of the pressure effects was shown to occur, as seen by recovery of polarization. An increase in Ca2+ concentration from 50 microM to 5 mM and of pH from 6.9 to 8.6 were found to increase the midpoint dissociation pressure, indicating that these factors stabilize the dimeric state. The hydrolytic activity of the ATPase was measured under pressure. The activity was inhibited by pressure increase. It was found that an irreversible inactivation of the solubilized enzyme occurred during turnover and that increasing pressure added to this instability. Reversibility of the activity was critically dependent on the presence of 10 mM Ca2+ in the assay medium.

Adenosine Triphosphatases↗
PubMed1986

Phenomenological description of the association of protein subunits subjected to conformational drift. Effects of dilution and of hydrostatic pressure.

The native conformation of oligomers may be expected to undergo reversible changes when they separate upon dissociation of the original aggregate. When these changes are slow in comparison with the time of an association-dissociation (AD) cycle, they give rise to characteristic effects in the dependence of the dissociation: upon dilution, at constant pressure, and upon the applied pressure, at constant concentration. The phenomenological description of these effects is examined by comparing two possible models: The first model assumes a continuous loss in free energy of association with the extent of dissociation; the second supposes the existence of two or more distinct aggregates differing in subunit affinity and present in proportions that vary with the extent of dissociation. The latter model fits better the experimental data available, with regard to both the concentration and the pressure dependence of the association, and gives a particularly simple explanation of the hysteresis phenomena observed in several oligomeric proteins after application of pressure. The validity of the principle of detailed balance, often assumed in dealing with complex equilibria, is discussed in detail as it does not appear possible to reconcile it with some of the experimental observations or with the proposed model.

Hydrostatic Pressure↗
PubMed1986

Conformational drift of dissociated lactate dehydrogenases.

Bovine and porcine lactate dehydrogenases, in solutions of 0.1-10 microM at neutral pH, dissociate into monomers upon application of hydrostatic pressures of up to 2 kbar. The dissociation was determined from observations of the polarization of fluorescence under pressure in seeming equilibrium conditions and by occasional hybridization experiments of the H4 and M4 isozymes. Decompression is followed by the rapid association of the monomers into tetramers and by slow, and sometimes incomplete, return of the enzymic activity. The dissociation curves obtained on compression and decompression differ, indicating that association results in partial loss of subunit affinity. These phenomena are attributed to a slow conformational drift that follows the loss of contact of the monomers with each other and to an even slower reversal of the drift that takes place upon reassociation.

Animals↗
PubMed1986

Conformational drift and cryoinactivation of lactate dehydrogenase.

Solutions of porcine lactate dehydrogenase of micromolar concentration kept at 4 degrees C for several days lose the greater part of their enzymic activity but recover it when returned to room temperature. The rate of spoiling decreases and the rate of recovery increases with the concentration of the solutions. The decrease in tetramer stability in the cold is shown by experiments of pressure dissociation at various temperatures and confirmed because isozyme hybridization occurs in parallel with the inactivation at low temperature but is absent at room temperature. Cold-inactivated solutions contain tetramers that dissociate much more readily than those of the fully active solutions. It is postulated that cryoinactivation, like pressure inactivation, takes place through a cycle of dissociation, conformational drift [King, L., & Weber, G. (1986) Biochemistry (second paper of three in this issue)] and reassociation into inactive tetramers.

Animals↗
PubMed1986

Selective sensitivity to tiazofurin of human leukemic cells.

This study reports the selective sensitivity to tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC-286193) of human leukemic leukocytes as compared to normal ones in bone marrow and peripheral blood samples by comparing the production of the active metabolite, thiazole-4-carboxamide adenine dinucleotide (TAD), from labeled tiazofurin and the depression of GTP concentration. When labeled tiazofurin was incubated with leukocytes obtained from healthy volunteers or from leukemic patients (acute non-lymphocytic leukemia or acute lymphoblastic leukemia), the TAD production was 27.0 +/- 8.3, 551.3 +/- 71.8 and 755.9 +/- 94.1 pmoles/10(9) cells per hr, respectively. Thus, the leukemic cells produced over 20-fold higher concentrations of TAD than the normal leukocytes. Incubation with tiazofurin in leukemic leukocytes decreased the GTP pools (to 48-79%), whereas there was no change in the normal leukocytes. These results indicate a selectivity of response to tiazofurin in human normal and leukemic leukocytes. The procedure reported in this work may be suitable as a rapid predictive test for the sensitivity of leukemic leukocytes to tiazofurin. Such a diagnostic test should be helpful in identifying neoplastic cells sensitive to tiazofurin in the Phase II trials now being developed.

Adenine Nucleotides↗
PubMed1986

Mechanism of resistance to tiazofurin in hepatoma 3924A.

Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC-286193) has shown potent cytotoxic and antitumor activity against hepatoma 3924A carried in the rat [Lui et al. J. biol. Chem. 259, 5078 (1984)]. However, eventually the tumor emerged, proliferated and killed the host. To throw light on the factors that play a role in the resistance to this drug, a tiazofurin-induced resistant hepatoma 3924A line in culture was produced, and its biochemical and pharmacological pattern was examined. Resistance in hepatoma cells was expressed by a reprogramming of gene expression that entailed the display of a program of multiple biochemical alterations. In the resistant cells the activity of IMP dehydrogenase, the target enzyme of tiazofurin, was increased 2- to 3-fold. The steady-state guanylate pools were elevated 3-fold, and there was a decrease in the de novo synthesis of guanylate. There was an expansion of guanylate salvage, which could circumvent inhibition of de novo guanylate synthesis by tiazofurin. For the first time in studies on the resistance of different cell lines to tiazofurin, reduced tiazofurin transport (to 50%) in resistant hepatoma cells was identified which might account for the decreased concentration (50%) of the active metabolite, thiazole-4-carboxamide adenine dinucleotide (TAD), in these cells. NAD pyrophosphorylase activity also decreased to 53% of that of the sensitive line, which was responsible, in part at least, for the decreased TAD concentration of the resistant cells. When resistant cells were cultured in the absence of tiazofurin, resistance to the drug gradually decreased, and by 50 passages sensitivity returned. Resistance to tiazofurin in hepatoma cells appears to be a drug-induced metabolic adaptation which involves alterations in the activity of the target enzyme, in the transport and concentration of the drug and the active metabolite, and an increase of guanylate concentration and guanine salvage capacity.

Adenosine Monophosphate↗
PubMed1986

Enzymic imbalance in serine metabolism in rat hepatomas.

The activity of 3-phosphoglycerate dehydrogenase was high in tissues of high cell-renewal capacity, and was increased in neonatal and regenerating liver and, more markedly, in hepatomas. Serine hydroxymethyltransferase activity was present in hepatomas, whereas other enzymes of serine utilization (serine dehydratase and serine aminotransferase) were absent. This enzymic imbalance couples serine biosynthesis preferentially to nucleotide precursor formation in cancer cells.

Animals↗
PubMed1986

Ultrastructural modifications of the platelet plasma membrane in vascular diseases and the effect of a carbochromen derivative as studied by freeze-fracture and computer measurement.

A high surface density of the openings of the surface connected canalicular system (SCCS) has been observed in the freeze-fractured plasma membrane of circulating platelets in rabbits fed an atherogenic diet and in hypercholesterolemic type IIa patients. In vitro tests have revealed a correlation between the increased surface density of the SCCS openings and the initial steps of platelet activation. 8-Chlorocarbochromen, a new drug which enhances the in vivo release of prostacyclin from the arterial wall, has been found to be effective in reducing the high surface density of SCCS openings in platelets of rabbits on an atherogenic diet. The present study shows that circulating platelets from patients with peripheral vascular disease present a high surface density of SCCS openings compared to that observed in control subjects. After a single oral administration of 8-chlorocarbochromen, a reduction of the high number of these openings has been observed. Likewise, beta-thromboglobulin levels were found to be high in the patients and to be significantly reduced after oral administration of the drug. This study shows ultrastructural modifications of platelets in conditions related to atherosclerosis and includes data on the effectiveness of 8-chlorocarbochromen in reducing the platelet activation of these patients.

Administration, Oral↗
PubMed1986

Regulation of carbamoyl-phosphate synthase II.

Evidence was provided that in rat liver synthase II activity, amount and turnover were regulated primarily by insulin. When rats were starved, synthase II activity and the immunotitratable enzyme amount markedly decreased; refeeding restored enzyme activity and amount to normal range. The changes in activity and amount were paralleled with alterations in the level of circulating insulin in the plasma. When starved rats were treated with anti-insulin serum before and during refeeding, the animals consumed the food, but the rise in synthase II activity was prevented. In diabetic rats, the activity and amount of synthase II in the liver markedly decreased and insulin treatment restored them to normal range. Actinomycin treatment prevented the refeeding and the insulin-induced rise in synthase II activity and amount. Study of the turnover of synthase II showed that in starvation the rate of synthesis decreased and refeeding restored the enzyme synthetic and degradation rates to normal range. In the diabetic rat, synthase II synthetic rate markedly decreased, and the degradation rate increased. Insulin returned the synthetic and catabolic rates to normal livers. In rapidly growing rat hepatoma 3924A, synthase II activity and amount were elevated 9- to 10-fold. Turnover studies showed that the synthetic rate in hepatoma 3924A was approximately 10-fold higher than that of normal liver. The catabolic rates of synthase II were similar in the liver and hepatoma. Thus, the increased activity and amount of synthase II in the hepatoma was due primarily to an increased rate of enzyme biosynthesis. Evidence was presented that in starvation and diabetes and on refeeding and insulin administration there is very little or no change in the enzymic activity, amount and turnover of hepatoma synthase II. The marked contrast between the turnover rate of hepatoma 3924A synthase II activity and that of the normal liver enzyme in starvation and in diabetes is under investigation. This overview of the behavior of activity, amount and turnover of synthase II in liver and hepatoma 3924A provides evidence of the important role of insulin in regulation of liver synthase II and of the apparent lack of responsiveness of the hepatoma enzyme to insulin concentrations. The precise details of the experimental procedures and the enzymic results will be published elsewhere.

Animals↗
PubMed1986

[Psychopathologic changes in chronic schizophrenic patients following withdrawal of neuroleptics: relation to therapeutic, neuroendocrine and computer tomography variables].

The following data were obtained from 36 male chronic schizophrenics (ICD 295.6) of 47 +/- 11 years of age, treated with neuroleptics for the last 16 +/- 6 years: Age, age at first manifestation of disease, duration and dosage scheme of neuroleptic therapy and number of electroconvulsive shock treatments. Blood samples were drawn both under neuroleptic treatment and after a 12-day withdrawal of neuroleptics, for determining cortisol, prolactin, beta-endorphin and noradrenaline. Psychopathology was assessed by standard criteria via BPRS. In 27 patients CT determination was carried out to determine the breadth of the third ventricle and the ventricular brain ratio. Withdrawal of neuroleptics resulted in a marked improvement, whereas 11 patients showed pronounced deterioration of their psychotic symptoms. In respect of the entire group there was a significant improvement of anergy, while disturbances of thinking were significantly enhanced. Serum levels of beta-endorphin and cortisol increased after neuroleptic withdrawal, whereas the levels of prolactin and of noradrenaline dropped. A considerable proportion of the patients showed a distinct extension of the ventricular system, but the CT variables correlated only slight with psychopathological parameters or their changes after neuroleptic withdrawal. The other variables, too, were without clinically relevant prognostic importance compared with the psychopathological changes after neuroleptic withdrawal. These variables were e.g. demography, psychopathology, therapy and neuroendocrinology.

Adult↗
PubMed1986

Features of families with major affective disorders.

This article reports the authors' observations on 22 families in which a young adult member has been diagnosed as manic-depressive, and on 11 families in which a member has been diagnosed as suffering from major schizoaffective disorder. All families could be described as extremely rigid and bound-up systems. Many of them were characterized by a "restrictive parental complementarity" and reciprocal delegation, and they shared certain cognitive features and assumptions. "Manic-depressive" families showed similarities as well as differences when compared with families in which there were schizophrenic and serious psychosomatic disorders.

Bipolar Disorder↗