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C Grebing

Publications and source records attributed to C Grebing.

17 recordsLinked to original sources
PubMed1991

Modification of transplasma membrane oxidoreduction by SV40 transformation of 3T3 cells.

Transformation of 3T3 cells by SV40 virus changes the properties of the transplasma membrane electron transport activity which can be assayed by reduction of external ferric salts. After 42 h of culture and before the growth rate is maximum, the transformed cells have a much slower rate of ferric reduction. The change in activity is expressed both by change in Km and Vmax for ferricyanide reduction. The change in activity is not based on surface charge effect or on tight coupling to proton release or on intracellular NADH concentration. With transformation by SV40 virus infection the expression of transferrin receptors increases, which correlates with greater diferric transferrin stimulation of the rate of ferric ammonium citrate reduction in transformed SV40-3T3 cells than in 3T3 cells.

3T3 Cells↗
PubMed1987

Involvement of transferrin in the reduction of iron by the transplasma membrane electron transport system.

Nonpermeable electron acceptors can be reduced by a transplasma membrane electron transport system in suspensions of intact cells. Here we report that diferric transferrin is reduced by HeLa S3 cells. The reduction is recorded spectrophotometrically as the formation of the ferrous complex of bathophenanthroline disulfonate. Ferric ammonium citrate can also be used as an electron acceptor and the presence of low concentrations of diferric transferrin greatly stimulates the reduction of trivalent iron under these conditions. Likewise very low concentrations of ferricyanide, which does not give rise to a ferrous bathophenanthroline disulfonate complex formation, have a strong stimulatory effect on the complex formation when ferric ammonium citrate is the source of ferric iron. Apotransferrin is a potent inhibitor of the reaction. The inhibition occurs at the concentration necessary for complete occupancy of the transferrin receptors. The inhibition can be demonstrated also when high concentrations of ferricyanide are used as electron acceptor. The possible mechanism behind the reported phenomena is discussed, and it is concluded that the transplasma membrane electron transport system can be involved in the process of cellular iron uptake.

Apoproteins↗
PubMed1986

Transplasmalemma electron transport from cells is part of a diferric transferrin reductase system.

Intact cells are known to reduce external, impermeable electron acceptors. We now show that cells can reduce the iron in diferric transferrin at the cell surface and that this reduction reaction depends on the transferrin receptor as well as the transmembrane electron transport system. Reduction of external diferric transferrin is accompanied by oxidation of internal NADH which indicates that the transmembrane enzyme is an NADH diferric transferrin reductase. Highly purified liver plasma membranes have NADH diferric transferrin reductase activity which shows properties similar to the diferric transferrin reductases activity of intact cells. Cell growth stimulation by diferric transferrin and other impermeable oxidants which can react with the diferric transferrin reductase can be based on electron transport through he plasma membrane.

Cell Membrane↗
PubMed1985

Transmembrane redox in control of cell growth. Stimulation of HeLa cell growth by ferricyanide and insulin.

The impermeable electron acceptor ferricyanide stimulates the growth of HeLa cells in the absence of serum and increases cell replication with limiting amounts of serum (0.75%). Maximum growth stimulation occurs at low ferricyanide concentration from 0.01 to 0.1 mM. Higher ferricyanide concentrations inhibit growth on serum. Addition of insulin enhances the stimulating effect of ferricyanide. Increase in the transplasmalemma electron transport activity in the presence of insulin is also observed by measuring the rate of ferricyanide reduction by cells. There is a close correlation between insulin stimulation of ferricyanide reduction and insulin induction of cell proliferation and attachment. In addition to ferricyanide, the growth response is observed with other impermeable oxidants, such as indigotetrasulfonate and hexaamine ruthenium III, which are reduced by the transplasma membrane electron transport system. Inactive oxidants such as cytochrome c do not stimulate cell growth. Ferrocyanide does not stimulate growth. We propose that electron flow through the transplasma membrane electron transport system stimulates growth and that insulin acts to increase that flow.

Blood↗
PubMed1985

Evidence for metabolic regulation of pancreatic glucagon secretion by L-glutamine.

To investigate effects by L-glutamine on pancreatic A-cell secretion and intermediary metabolism, isolated pancreatic islets from normal and streptozotocin treated guinea pigs (A-cell rich islets) were incubated in the presence of glucose (5.5 mM) +/- L-glutamine (10 mM). Glutamine significantly enhanced glucagon release from 297 +/- 54 to 528 +/- 53 pg/micrograms DNA/h in normal islets and from 553 +/- 31 to 806 +/- 50 pg/micrograms DNA/h in A-cell rich islets. All results were expressed on the basis of islet DNA concentration, being 66 +/- 4 ng DNA per normal islet and 32 +/- 2 ng DNA per A-cell rich islet. Simultaneously, glutamine suppressed glucose oxidation to 64 per cent in normal islets and to 47 per cent of basal oxidation in A-cell rich islets. Islet content of ATP was also reduced by glutamine to about 60 per cent in A-cell rich islets, but not significantly changed in normal islets. Glutamine oxidation, at 5.5 mM-glucose, was considerably higher in A-cell rich islets (911 +/- 65 pmol/micrograms DNA/h) than in normal islets (313 +/- 52 pmol/micrograms DNA/h). Addition of porcine insulin (25 mU/ml) counteracted these effects by glutamine, i.e. suppressed glucagon release but increased glucose oxidation and ATP content of the A-cell rich islets. The present findings demonstrate that glutamine stimulates glucagon release and is readily metabolized by the A-cells. Furthermore, the regulation of glucagon secretion by glutamine appears to be reciprocally related to factors affecting glucose metabolism and ATP-levels in the A-cell.

Adenosine Triphosphate↗
PubMed1984

Transplasma membrane redox stimulates HeLa cell growth.

Impermeable ferricyanide stimulates the growth of HeLa cells in absence of fetal bovine serum or other growth factors. A series of impermeable oxidants with redox potentials down to -125 mV stimulate equivalent growth. All of these oxidants are reduced by the transplasma membrane electron transport system. Oxidants with redox potentials below -175 mV are not reduced by the transmembrane electron transport and do not stimulate growth. Insulin which stimulates growth in absence of serum also stimulates transmembrane ferricyanide reduction. Ferricyanide increases growth in presence of insulin. Antitumor drugs, which inhibit HeLa cell growth, inhibit the transplasma membrane redox system. Transplasma membrane electron transport is accompanied by proton release from HeLa cells.

Cell Division↗
PubMed1984

A transmembranous NADH-dehydrogenase in human erythrocyte membranes.

Evidence is presented for a transmembranous NADH-dehydrogenase in human erythrocyte plasma membrane. We suggest that this enzyme is responsible for the ferricyanide reduction by intact cells. This NADH-dehydrogenase is distinctly different from the NADH-cytochrome b5 reductase on the cytoplasmic side of the membrane. Pretreatment of erythrocytes with the nonpenetrating inhibitor diazobenzene sulfonate (DABS) results in a 35% loss of NADH-ferricyanide reductase activity in the isolated plasma membrane. Since NADH and ferricyanide are both impermeable, the transmembrane enzyme can only be assayed in open membrane sheets with both surfaces exposed, and not in closed vesicles. The transmembrane dehydrogenase has affinity constants of 90 microM for NADH and 125 microM for ferricyanide. It is inhibited by p-chloromercuribenzoate, bathophenanthroline sulfonate, and chlorpromazine.

Cytochrome Reductases↗
PubMed1984

Properties of a transplasma membrane electron transport system in HeLa cells.

A transmembrane electron transport system has been studied in HeLa cells using an external impermeable oxidant, ferricyanide. Reduction of ferricyanide by HeLa cells shows biphasic kinetics with a rate up to 500 nmoles/min/g w.w. (wet weight) for the fast phase and half of this rate for the slow phase. The apparent Km is 0.125 mM for the fast rate and 0.24 mM for the slow rate. The rate of reduction is proportional to cell concentration. Inhibition of the rate by glycolysis inhibitors indicates the reduction is dependent on glycolysis, which contributes the cytoplasmic electron donor NADH. Ferricyanide reduction is shown to take place on the outside of cells for it is affected by external pH and agents which react with the external surface. Ferricyanide reduction is accompanied by proton release from the cells. For each mole of ferricyanide reduced, 2.3 moles of protons are released. It is, therefore, concluded that a transmembrane redox system in HeLa cells is coupled to proton gradient generation across the membrane. We propose that this redox system may be an energy source for control of membrane function in HeLa cells. The promotion of cell growth by ferricyanide (0.33-0.1 mM), which can partially replace serum as a growth factor, strongly supports this hypothesis.

Cell Division↗
PubMed1984

Inhibition of plasma membrane NADH dehydrogenase by adriamycin and related anthracycline antibiotics.

Doxorubicin (adriamycin) is cytotoxic to cells, but the biochemical basis for this effect is unknown, although intercalation with DNA has been proposed This study suggests that the cytotoxicity of this drug may be due to inhibition of the plasma membrane redox system, which is involved in the control of cellular growth. Concentrations between 10(-6) - 10(-7) M adriamycin inhibit plasma membrane redox reactions greater than 50%. AD32, a form of adriamycin which does not intercalate with DNA, but is cytotoxic, also inhibits the plasma membrane redox system. Thus, the cytotoxic effects of adriamycin, which limit its use as a drug, may be based on the inhibition of a transplasma membrane dehydrogenase involved in a plasma membrane redox system.

Animals↗
PubMed1983

Transformed liver cells have modified transplasma membrane redox activity which is sensitive to adriamycin.

Electron transport across the plasma membrane is found in all cells which have been tested. This activity has been implicated in control of cellular growth, transport and hormone response. In virus transformed cells and tumor cells we find the activity is decreased and becomes sensitive to the antitumor drug adriamycin. Inhibition of transmembrane redox by adriamycin parallels cytoxicity to transformed cells.

Animals↗
PubMed1983

NADH-monodehydroascorbate reductase in human erythrocyte membranes.

Enzymatic activity of NADH-monodehydroascorbate reductase could be observed in red blood cell membranes. This activity was latent in right side out as well as inside out vesicles. Apart from this latency addition of certain detergents led to activation of the enzyme also in open membrane preparations. The enzyme was inhibited by metal chelators, and displayed a very low apparent Michaelis constant. Monodehydroascorbate is a candidate for the natural electron acceptor of the transmembrane NADH-oxido-reductase. The activation by detergent may be due to enhancement of lipid fluidity or to exposure of a lipophilic substrate binding site.

Erythrocyte Membrane↗
PubMed1982

Insulin control of a transplasma membrane NADH dehydrogenase in erythrocyte membranes.

A study of NADH ferricyanide reductase activity in oriented vesicles or open ghosts of human and porcine erythrocytes shows that the dehydrogenase activity can have three types of orientation in the membrane. There is activity which responds only to acceptors and NADH exclusively on the inside face, or exclusively on the outer surface. There is also activity which requires exposure of both sides of the membrane and thus is transmembranous. The transmembrane activity is inhibited by insulin, whereas the internal and external enzymes do not respond to insulin. The transmembrane dehydrogenase can be a basis for proton transport in the plasma membrane.

Animals↗
PubMed1981

Evidence for the extracellular reduction of ferricyanide by rat liver. A trans-plasma membrane redox system.

1. Reduction of ferricyanide by the isolated perfused rat liver and by isolated rat hepatocytes was studied. 2. Ferricyanide was reduced to ferrocyanide by the perfused liver at a linear rate of 0.22mumol/min per g of liver. Ferricyanide was not taken up by the liver and the perfusate concentration of ferricyanide+ferrocyanide remained constant throughout the perfusion. Perfusate samples from livers perfused without ferricyanide did not reduce ferricyanide. 3. Isolated hepatocytes reduced ferricyanide in a biphasic manner. The initial rate of 2.3mumol/min per g of cells proceeded for approx. 3min and derived from low-affinity sites (apparent K(m)>1.3mm). The secondary rate of 0.29mumol/min per g of cells was maintained for the remainder of the incubation and derived from higher affinity sites (apparent K(m)0.13mm). Disruption of the cells resulted in an increase in the low-affinity rate and a decrease in the high-affinity rate. 4. Ferrocyanide was oxidized by isolated hepatocytes but not by perfused liver. The apparent K(m) for ferrocyanide oxidation by hepatocytes was 1.3mm. 5. Oxidized cytochrome c was reduced by isolated hepatocytes in the presence of 1mm-KCN but at a rate less than that of the reduction of ferricyanide. 6. Properties of the ferricyanide-reducing activities of intact hepatocytes and the perfused liver were examined. The low-affinity rate, present only in cell and broken cell preparations, was inhibited by 1mum-rotenone and 0.5mm-ferrocyanide, and stimulated by 0.1mm-KCN. The mitochondrial substrate, succinate, also stimulated this rate. The perfused liver showed only a high-affinity activity for ferricyanide reduction. This activity was also present in liver cells and was unaffected by rotenone, antimycin A, KCN, NaN(3), or p-hydroxymercuribenzoate but was inhibited by 2.6mm-CaCl(2), 2-heptyl-4-hydroxyquinoline-N-oxide and ferrocyanide. Overall, these results are consistent with the occurrence of a trans-plasma membrane redox system of liver that reduces extracellular ferricyanide to ferrocyanide. The reduction process shows properties which are similar to that of the NADH:ferricyanide oxidoreductase found in isolated liver plasma membranes but different from that of mitochondria.

Animals↗