scholarly journals Differential uptake of [3H]guanosine by nucleoside transporter subtypes in Ehrlich ascites tumour cells

1992 ◽  
Vol 287 (2) ◽  
pp. 431-436 ◽  
Author(s):  
J R Hammond
Keyword(s):  
Mammalian Cells ◽  
Nucleoside Transport ◽  
Transport Systems ◽  
Nucleoside Transporter ◽  
Ehrlich Ascites ◽  
Ehrlich Ascites Tumour ◽  
Transport Inhibitors ◽  
Influx Kinetics ◽  
Ascites Tumour Cells ◽  
Ehrlich Ascites Tumour Cells

Intracellular metabolism of [3H]guanosine was minimal (< 15%) during the first 22 s of incubation, and hence reasonable estimates of initial-rate influx kinetics could be derived by using metabolically active cells. Na(+)-dependent concentrative [3H]guanosine uptake was not observed. Data suggest that [3H]guanosine was accumulated primarily via the nitrobenzylthioguanosine (NBTGR)-sensitive subtype of facilitated nucleoside transporter. Incubation of cells with 100 nM-NBTGR significantly decreased the potency of guanosine as an inhibitor of [3H]uridine influx. The Vmax. for [3H]guanosine influx (9.2 pmol/s per microliters) was significantly lower than that for [3H]uridine influx (16 pmol/s per microliters). The Km for transporter-mediated [3H]guanosine influx determined in the presence of 100 nM-NBTGR was 16-fold higher (1780 microM) than that determined in its absence, whereas the Km for [3H]uridine influx was shifted by only 2-fold. In other respects, the cellular accumulations of [3H]guanosine and [3H]uridine were similar; both had Km values of approx. 140 microM for total mediated influx, and both were inhibited similarly by other nucleosides and transport inhibitors. These characteristics, and the fact that guanosine is an endogenous nucleoside, suggest that [3H]guanosine may prove useful as a poorly metabolized, relatively selective, substrate for study of the NBTGR-sensitive nucleoside transport systems of mammalian cells.

scholarly journals The pathway of glutamine and glutamate oxidation in isolated mitochondria from mammalian cells

1971 ◽  
Vol 125 (3) ◽  
pp. 757-763 ◽  
Author(s):  
Zoran Kovačević
Keyword(s):  
Glutamate Dehydrogenase ◽  
Mammalian Cells ◽  
Tumour Cells ◽  
Co2 Production ◽  
Isolated Mitochondria ◽  
Ascites Tumour ◽  
Ehrlich Ascites ◽  
Ehrlich Ascites Tumour ◽  
Ascites Tumour Cells ◽  
Ehrlich Ascites Tumour Cells

1. Pyruvate strongly inhibited aspartate production by mitochondria isolated from Ehrlich ascites-tumour cells, and rat kidney and liver respiring in the presence of glutamine or glutamate; the production of14CO2 from l-[U-14C]glutamine was not inhibited though that from l-[U-14C]glutamate was inhibited by more than 50%. 2. Inhibition of aspartate production during glutamine oxidation by intact Ehrlich ascites-tumour cells in the presence of glucose was not accompanied by inhibition of CO2 production. 3. The addition of amino-oxyacetate, which almost completely suppressed aspartate production, did not inhibit the respiration of the mitochondria in the presence of glutamine, though the respiration in the presence of glutamate was inhibited. 4. Glutamate stimulated the respiration of kidney mitochondria in the presence of glutamine, but the production of aspartate was the same as that in the presence of glutamate alone. 5. The results suggest that the oxidation of glutamate produced by the activity of mitochondrial glutaminase can proceed almost completely through the glutamate dehydrogenase pathway if the transamination pathway is inhibited. This indicates that the oxidation of glutamate is not limited by a high [NADPH]/[NADP+] ratio. 6. It is suggested that under physiological conditions the transamination pathway is a less favourable route for the oxidation of glutamate (produced by hydrolysis of glutamine) in Ehrlich ascites-tumour cells, and perhaps also kidney, than the glutamate dehydrogenase pathway, as the production of acetyl-CoA strongly inhibits the first mechanism. The predominance of the transamination pathway in the oxidation of glutamate by isolated mitochondria can be explained by a restricted permeability of the inner mitochondrial membrane to glutamate and by a more favourable location of glutamate–oxaloacetate transaminase compared with that of glutamate dehydrogenase.

scholarly journals Solubilization and reconstitution of a nucleoside-transport system from Ehrlich ascites-tumour cells

1989 ◽  
Vol 262 (1) ◽  
pp. 109-118 ◽  
Author(s):  
J R Hammond ◽  
R M Johnstone
Keyword(s):  
Transport System ◽  
Human Erythrocyte ◽  
Plasma Membranes ◽  
Nucleoside Transport ◽  
Ehrlich Cell ◽  
Ascites Tumour ◽  
Ehrlich Ascites ◽  
Ehrlich Ascites Tumour ◽  
Ascites Tumour Cells ◽  
Ehrlich Ascites Tumour Cells

Uptake of [3H]uridine by Ehrlich cells was mediated by both nitrobenzylthioinosine (NBMPR)-sensitive (75%) and NBMPR-insensitive (25%) mechanisms. Each cell contained approx. 26,000 high-affinity (KD = 0.19 nM) recognition sites for [3H]NBMPR, and binding was inhibited by dipyridamole and adenosine at concentrations similar to those required for inhibition of [3H]uridine uptake. Calculations show that each cell contains a total of about 35,000 nucleoside transporters. Photoaffinity labelling of a partially purified preparation of plasma membranes with [3H]NBMPR resulted in a single broad 3H-labelled band on SDS/polyacrylamide gels, with an apparent molecular-mass peak of 42 kDa. This is in contrast with human erythrocyte membranes, where [3H]NBMPR photolabelled two broad bands with peaks at 55 and 80 kDa. Treatment of photoaffinity-labelled membranes with endoglycosidase F decreased the apparent molecular masses of both the Ehrlich-cell and erythrocyte [3H]NBMPR-labelled proteins to approx. 40 kDa. These results suggest that the human erythrocyte [3H]NBMPR-binding polypeptides are more extensively glycosylated than the corresponding Ehrlich-cell polypeptides. Octyl beta-D-glucopyranoside [1.0% (w/v) + asolectin] solubilized over 90% of the [3H]NBMPR-binding sites, with near-complete retention of [3H]NBMPR-binding characteristics. The only major change was a 65-fold decrease in affinity for dipyridamole, which was partly reversed upon incorporation of the solubilized proteins into asolectin membranes. Proteoliposomes, prepared by using asolectin and the octyl glucoside-solubilized plasma membranes, were capable of accumulating [3H]uridine via a protein-dependent dipyridamole/nitrobenzylthioguanosine/dilazep-sensitive mechanism. We have thus demonstrated the efficient solubilization and functional reconstitution of a nucleoside-transport system from Ehrlich ascites-tumour cells.

scholarly journals The transport and oxidation of succinate by Ehrlich ascites-tumour cells

1976 ◽  
Vol 160 (1) ◽  
pp. 121-123 ◽  
Author(s):  
T L Spencer
Keyword(s):  
Ph Dependence ◽  
Organic Anion ◽  
Tumour Cells ◽  
Cell Integrity ◽  
Carrier System ◽  
Ascites Tumour ◽  
Ehrlich Ascites ◽  
Ehrlich Ascites Tumour ◽  
Ascites Tumour Cells ◽  
Ehrlich Ascites Tumour Cells

The transport and oxidation of succinate by functionally intact Ehrlich ascites-tumour cells was investigated. On the basis of pH dependence and inhibitor sensitivity it was concluded that succinate may be transported across the cell membrane by the organic anion carrier system. Thus the ability of isolated Ehrlich cells to oxidize succinate is real, and is not necessarily a result of damage to cell integrity.

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