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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Concentrations of intracellular orthophosphate were determined in Ehrlich ascites tumor cells incubated with glucose, inosine, or uridine in media of different orthophosphate concentration. The effects of orthophosphate concentration on the accumulation of lactate and of phosphoribosyl pyrophosphate and on concentrations of ribose 1-phosphate and ribose 5-phosphate in tumor cells incubated with glucose were also determined. Both the phosphorolysis of inosine and the rate of catabolism of ATP in cells incubated with 2-deoxyglucose were also influenced by the orthophosphate concentration of the medium.
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PMID:Role of orthophosphate concentration in the regulation of ribose phosphate synthesis and purine metabolism in Ehrlich ascites tumor cells. 56 Sep 2

This study was undertaken to examine the mechanism by which metabolic inhibition reduces amino acid active transport in ehrlich ascites tumor cells. At 37 degrees C the metabolic inhibitor combination 0.1 mM 2,4-dinitrophenol (DNP) + 10 mM 2- deoxy-D-glucose (DOG) reduced the cell ATP concentration to 0.10- 0.15 mM in less than 5 min. This inhibition was associated with a 20.6 percent +/- 6.4 percent (SD) decrease in the initial influx of alpha-aminoisobutyric acid (AIB), and a two- to fourfold increase in the unidirectional efflux. These effects could be dissociated from changes in cell Na(+) or K(+) concentrations. Cells incubated to the steady state in 1.0-1.5 mM AIB showed an increased steady-state flux in the presence of DNP + DOG. Steady- state fluxes were consistent with trans-inhibition of AIB influx and trans-stimulation of efflux in control cells, but trans- stimulation of both fluxes in inhibited cells. In spite of the reduction of the cell ATP concentration to less than 0.15 mM and greatly reduced transmembrane concentration gradients of Na(+) and K(+), cells incubated to the steady state in the presence of the inhibitors still established an AIB distribution ration 13.8 +/- 2.6. The results are interpreted to indicate that a component of the reduction of AIB transport produced by metabolic inhibition is attributable to other actions in addition to the reduction of cation concentration gradients. Reduction of cell ATP alone is not responsible for the effects of metabolic inhibition, and both the transmembrane voltage and direct coupling to substrate oxidation via plasma-membrane-bound enzymes must be considered as possible energy sources for amino acid active transport.
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PMID:A reassessment of decreased amino acid accumulation by Ehrlich ascites tumor cells in the presence of metabolic inhibitors. 56 Nov 60

Optimal DNA synthesis in isolated Ehrlich ascites tumor cell nuclei depends upon the presence of ATP. The increased synthesis in the presence of ATP is shown to be due primarily to increased synthesis per active site rather than initiation of synthesis at different sites. The size of the short pieces observed in the presence of ATP is larger than the corresponding pieces observed in the absence of ATP.
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PMID:Nature of DNA synthesized in the presence of ATP in isolated nuclei. 56 77

The addition of glucose to ELD and ELT/B1 mouse ascites tumor cell suspensions caused a 2.3-fold increase in the phosphorylation state ratio, (ATP)/(ADP) (Pi), because of a decrease in the intracellular Pi concentration. The addition of glucose to these cell suspensions has been reported by Chance and Hess ('59) to cause an increase in the study state reduction of cytochrome b and an increase in the steady state oxidation of cytochrome c. On a quantitative basis these two independent measurements suggest that a near equilibrium exists between the oxidation-reduction state of the mitochondrial electron carriers and the reactions of ATP synthesis (as expressed by the phosphorylation state ratio) both before and after glucose addition. We conclude that the mechanism of the inhibition of respiration by glycolysis (the Crabtree effect) is a decrease in the rate of electron transport caused by the mass action effect of the elevated phosphorylation state ratio.
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PMID:On the mechanism of the Crabtree effect in mouse ascites tumor cells. 56 9

Ribonucleotide reductase from Ehrlich tumor cells was separated by chromatography on blue dextran/Sepharose into two protein fractions (Tris and Dye fractions). Neither fraction alone had reductase activity, but when combined, constituted an active enzyme system. Heat treatment of either fraction resulted in an inactive combination. The approximate molecular size of the active component of the Tris and Dye fractions was determined to be 5.7 S and 6.5 S, respectively, compared to 9 S for the intact enzyme. The Tris fraction was inactivated by hydroxylamine while the dye fraction was inactivated by pyridoxal phosphate/BH4-treatment. The inactivation of the Dye fraction was prevented by ATP. These data would indicate that the Tris and Dye fractions were comparable in function to the B2 and B1 proteins, respectively, of the Escherichia coli ribonucleotide reductase.
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PMID:Reconstitution of the ribonucleotide reductase enzyme from Ehrlich tumor cells. 56 57

A regulatory function of the cell membrane in controlling the cytoplasmic level of Pi has been proposed, and in Ehrlich ascites tumor cells an active influx of primary phosphate has been reported in the literature. In the present study, Ehrlich cells were incubated at 1.5--50 mM extracellular Pi at pH 7.4 (Pi mainly secondary phosphate) and at pH 6.0 (mainly primary phosphate), and the measured cell Pi was compared with the value expected from a passive distribution of Pi. At a low extracellular Pi concentration the cell Pi was 3--6 mumol/g or even more. It is suggested that a major part of this cell Pi can be accounted for by enzymic release of Pi during the sampling procedure. If this interpretation is correct, the present results show that both ionic species of Pi are in electrochemical equilibrium across the cell membrane at steady state. Moreover, in vivo the concentration of free Pi in the cytosol will presumably be maintained at a steady-state level of about 0.4 mM, one order of magnitude below the directly measured values. This implies that the ratio [ATP]/[ADP][Pi] which is important in the regulation of energy metabolism, is higher than reported in the literature.
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PMID:Inorganic phosphate in Ehrlich ascites tumor cells and its distribution across the cell membrane. 56 66

In late stages of Ehrlich tumor development there occurs a gradual increase of the portion of cells, being in the second half of the mitotic cycle, on account of cells of the initial stages of mitosis. Simultaneously, resting cells are accumulated. The data of energy metabolism may account for these changes in the population structure. Under conditions of the glucose deficiency accompanying tumor growth the ATP deficit proves to be greater in cells of the second half of the mitotic cycle than in cells of the beginning of mitosis, thus resulting in redistribution of cells with stages of the mitotic cycle. In an old tumor the rate of DNA synthesis was shown to be lower at all stages of S-phase, while RNA synthesis was mostly activated in cells of G-period. In S- and G2 cells of an old tumor the total protein content was reduced. In G0-cells nuclei of Ehrlich tumor electrophoresis in polyacrylamide gel would show protein with a molecular weight 9000 +/- 500, which was absent in proliferating cells nuclei. It was demonstrated that protein with analagous properties is contained in nuclei of 13 transplantable animal tumors.
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PMID:[Changes in the structure of Ehrlich tumor cell populations]. 71 14

Effect of MgCl2 and ATP on the elevation in lactate, pyruvate and methylglyoxale content was studied on incubation of fructosediphosphate with muscle and tumor homogenates. Muscle homogenate accumulated lactate, pyruvate and methyglyoxale more intensively as compared with tumor homogenate. Pyruvate was formed only in presence of MgCl2 and ATP, although it did not practically affect the elevation of lactate in muscle homogenate. The data obtained suggest that tumor homogenate does not contain the enzymatic system involved in methylglyoxale formation.
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PMID:[Splitting of fructose diphosphate by muscle and tumor homogenates]. 88 55

The biochemistry and secretory characteristics of a transplantable rat pheochromocytoma have been studied. This tumor possesses the enzyme required for the biosynthesis of norepinephrine from tyrosine, and stores large amounts of norepinephrine (33 +/- 3 nmol/mg of protein). The tumor does not have detectable levels of noradrenalin N-methyltransferase, nor does it contain significant amounts of epinephrine. Approximately two-thirds of the catecholamine content, and one-half of the dopamine beta-monoxygenase activity in the tumor can be isolated in a granule fraction by sedimentation. This granule fraction also contains ATP; the molar ratio of catecholamine to ATP in this granule fraction (5.6 +/- 0.9) is similar to that found in granules prepared from normal adrenal glands. Cell suspensions were prepared by mechanical disruption of the tumor. Incubation of these cell suspensions in media containing 56 mM K+, or the divalant cation ionophores, lasolocid or A23187, leads to the release of catecholamine from these cells. The cells do not secrete catecholamine in response to acetycholine. Catecholamine release induced by 56 mM K+ appears to be by exocytosis, since this release is dependent upon extracellular Ca++, and is accompanied by the release of dopamine beta-monooxygenase, but not of lactate dehydrogenase, from the cells. The mechanism by which the ionophores stimulate catecholamine secretion has not been established.
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PMID:Studies of a transplantable rat pheochromocytoma: biochemical characterization and catecholamine secretion. 93 94

1. The regulatory properties of two interconvertible kinetic forms of class A pyruvate kinase from Ehrlich ascites tumor cells have been studied with a partially purified enzyme preparation free of interfering enzymatic activities. 2. The hyperbolic form shows Michaelis-Menten kinetics for P-pyruvate, with high affinity for this substrate and low affinity for the inhibitory amino acids alanine and phenylalanine. The sigmoidal form displays positive cooperativity respect to P-pyruvate (n=1.4), with lower affinity for this substrate and higher affinity for the inhibitory amino acids. 3. The equilibrium between the hyperbolic and the sigmoidal forms of the enzyme is affected by substraetes and effectors. P-pyruvate, ADP and Fru-P2 shift the equilibrium to the hyperbolic form while ATP, alanine and phenylalanine stabilize the sigmoidal form. 4. Effector metabolites affect the molecular weight of the protein, acting on an equilibrium between dimers and tetramers. P-pyruvate and ADP associate the enzyme to a tetramer while ATP, alanine and phenylalanine favor the occurrence as a dimer. The positive modifier Fru-P2 did not associate the enzyme to the tetramer, even at 1 mM concentration. 5. A tentative molecular model for pyruvate kinase A on the basis of the kinetic and aggregation interconversion is proposed.
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PMID:Interconversion phenomena between two kinetic forms of class a pyruvate kinase from Ehrlich ascites tumor cells. 100 94


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