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PubMed1998

Adenosine and hypoxanthine transport in horse erythrocytes: evidence for a polymorphism in the transport of hypoxanthine via a sodium-dependent cotransporter.

The inward transport of two purines, adenosine and hypoxanthine, at 37 degrees C by horse erythrocytes was compared. No mediated transport of adenosine was detected in horse erythrocytes, nor was saturable, high-affinity binding of the potent facilitated-diffusion inhibitor nitrobenzylthioinosine demonstrable in horse erythrocyte membranes. In contrast, erythrocytes from most horses possessed a saturable sodium-dependent hypoxanthine transporter (apparent K(m), 100 +/- 28 microM; Vmax, 0.20 +/- 0.08 mmol (l cells)-1 h-1; means +/- S.E.M., n = 5). Guanine inhibited hypoxanthine influx (apparent Ki, 24 +/- 6 microM), but adenine and xanthine had no effect. Unlike human erythrocytes, no sodium-independent hypoxanthine transporter was detected in horse erythrocytes. There are, however, a small number of animals (approximately 15%) whose erythrocytes fail to transport hypoxanthine. This variation appears to be under genetic control, but the precise nature of the control is unknown.

Adenosine↗
PubMed1972

Calcium-dependent amylase release and electrophysiological measurements in cells of the pancreas.

1. Transmembrane potential, effective membrane resistance, and amylase output were recorded from acinar cells of rat pancreas perfused in vitro.2. Both pancreozymin and acetylcholine hyperpolarized the acinar cells, increased effective membrane resistance, and augmented amylase output.3. The omission of calcium from the perfusion medium increased effective membrane resistance and potential, and abolished the increase in amylase output in response to the drugs.4. A quantitative relation was found between the amount of amylase released by pancreozymin and the concentration of calcium in the perfusion medium at values below the normal 2.5 mM calcium. Excess magnesium did not inhibit the increase in amylase output in response to the drug.5. It is concluded that the release of amylase from the pancreas depends on the entry of calcium into the acinar cells. The entry of calcium seems to be mediated by a carrier in the membrane and may be considered as a ;facilitated diffusion'.6. The electrophysiological findings taken together with morphological evidence provided by scanning electron microscopy favour the view that pancreatic zymogens are released from the granules in the acinar cells to the lumen by the process known as exocytosis.

Acetylcholine↗
PubMed1976

Stimulus-secretion coupling in pancreatic acinar cells: inhibitory effects of calcium removal and manganese addition on pancreozymin-induced amylase release.

The role of Ca ions in stimulus-secretion coupling has been analysed in the isolated and perfused rat pancreas. 2. The omission of [Ca2+]O diminished but did not abolish the release of amylase in response to continuous stimulation with 5 m-u. pancreozymin (Pz)/ml. The addition of Mn2+ (1-0 mM) to this Ca-deficient environment abolished the residual release of amylase. This was followed by a complete recovery of amylase output when the control [Ca2+]O was reestablished. 3. The addition of Mn2+ (1-0 mM) to the extracellular environment containing 2-5 mM-Ca2+ reversibly inhibited the Pz-induced release of amylase. 4. A kinetic scheme based on competition of Ca and Mn at a carrier in the acinar cell membrane could quantitatively explain the effects of Ca and Mn upon the Pz-induced amylase release. 5. These results support the view that the Ca2+ influx into the acinar cells is the major contributor to the rise in [Ca2+]i which, in turn, mediates the processes in the stimulus-secretion coupling in the exocrine pancreas, and suggest that the mode of Ca influx is a facilitated diffusion.

Amylases↗
PubMed1977

The hepatocellular uptake of glucose, galactose and fructose in conscious sheep.

1. Surgical techniques for chronic catheterization of hepatic and portal veins in the sheep are described. These catheters remained usable for 2-6 months and did not alter hepatic morphology. 2. Hepatocellular uptake of monosaccharides was estimated from their ability to pass the boundaries of the sucrose space in a double indicator dilution procedure in conscious fed sheep. 3. A large proportion (81%) of D-glucose carried in the portal blood was found to enter an hepatic cellular compartment. 4. The radioactive label of D-glucose infused in the portal vein remained associated with D-glucose in hepatic venous blood samples during the experimental period. 5. A large proportion (74%) of an infused trace of D-galactose, a smaller proportion (33%) of D-fructose, and negligible amounts of L-glucose were taken up in a single passage through the liver. 6. Raised blood concentrations of sucrose or of methyl-alpha-D-glucoside (Me-alpha-DG) significantly diminished the proportional uptake of D-glucose. Raised blood concentrations of glucose, galactose or Me-alpha-DG diminished the proportional uptake of D-galactose. Raised blood concentrations of fructose diminished the proportional uptake of fructose. 7. Neither total hepatic blood flow changes nor competitive effects within the cell could account for these findings. 8. It is concluded that these monosaccharides enter the liver cell by facilitated diffusion, and share at least some of the membrane elements that mediate this process. It seems likely that only a proportion of the glucose-transporting apparatus is accessible to galactose.

Animals↗
PubMed1978

Nucleoside transport in sheep erythrocytes: genetically controlled transport variation and its influence on erythrocyte ATP concentrations.

1. The permeability of sheep erythrocytes to purine and pyrimidine nucleosides was investigated. Erythrocytes from most sheep (nucleoside-impermeable) were almost completely impermeable to 5 mM inosine whereas cells from approximately 5% of the animals studied (nucleoside-permeable) showed a rapid inosine uptake. Cells from both types of animal were permeable to 5 mM adenosine, although transport was slower in nucleoside-impermeable erythrocytes. 2. Two distinct nucleoside transport routes were present in nucleoside-permeable erythrocytes; a high affinity (apparent Km congruent to 0.2 mM) facilitated diffusion system which transported both purine and pyrimidine nucleosides, and a non-saturable uptake route selective for adenosine. The high affinity system was the major route of adenosine transport at physiological concentrations. 3. Transport by the high affinity system was completely inhibited by micromolar concentrations of dipyridamole and nitrobenzylthioinosine. Dipyridamole had no effect on the non-saturable component of adenosine uptake. 4. The transport differences between nucleoside-permeable and impermeable erythrocytes were due to the absence of the high affinity system from nucleoside-impermeable cells. 5. Nucleoside-permeable cells had a higher intracellular ATP concentration than nucleoside-impermeable erythrocytes, suggesting that the high affinity transport system participates in the energy metabolism of the cell.

Adenosine Triphosphate↗
PubMed2000

Oatp2 mediates bidirectional organic solute transport: a role for intracellular glutathione.

One member of the OATP family of transporters, rat Oatp1, functions as an anion exchanger that is driven in part by the glutathione (GSH) electrochemical gradient, indicating that other OATP-related transporters may also be energized by this mechanism. The present study examined whether rat Oatp2 is also an anion exchanger, and, if so, whether it is energized by the GSH electrochemical gradient. As with Oatp1, uptake of 10 microM [(3)H]taurocholate in Oatp2-expressing Xenopus laevis oocytes was trans-stimulated by intracellular 0.2 mM unlabeled taurocholate, indicating bidirectional transport. Interestingly, [(3)H]taurocholate uptake in Oatp2-expressing oocytes was also trans-stimulated when oocytes were preloaded with GSH, S-methylglutathione, S-sulfobromophthalein-glutathione, S-dinitrophenyl glutathione, or ophthalmic acid (a GSH analog) but not by glutarate or N-acetylcysteine, suggesting that GSH derivatives and conjugates may function as intracellular substrates for Oatp2. Support for this hypothesis was provided by the demonstration of enhanced [(3)H]GSH and [(3)H]S-(2,4-dinitrophenyl)-glutathione efflux in Oatp2-expressing oocytes. However, in contrast to Oatp1, extracellular GSH failed to cis-inhibit uptake of [(3)H]taurocholate or [(3)H]digoxin in Oatp2-expressing oocytes, indicating that the stimulatory effect of high intracellular GSH concentrations is not due to a coupled exchange mechanism. Taken together, the results indicate that Oatp2 mediates bidirectional transport of organic anions by a GSH-sensitive facilitative diffusion mechanism and suggest that this transporter may play a role in cellular export of specific organic molecules.

Animals↗
PubMed1996

Multiple efflux mechanisms are involved in Candida albicans fluconazole resistance.

Fluconazole-susceptible Candida albicans strains accumulated [3H]fluconazole at a rate of approximately 2 pmol/min per 10(9) cells. Fluconazole accumulation was not affected by the pretreatment of cells with sodium azide or with 2-deoxyglucose. The rate of fluconazole accumulation became saturated at high fluconazole concentrations and was not affected by the addition of ketoconazole, and there was no fluconazole accumulation in cells incubated at 4 degrees C. A fluconazole-resistant mutant of C. albicans SGY-243 was isolated following growth enrichment in fluconazole-containing medium. Cells of the mutant strain, designated FR2, showed a reduced rate of fluconazole accumulation compared with SGY-243 and were not resistant to other azole antifungal agents. The rates of fluconazole accumulation by C. albicans FR2 and the other azole-resistant strains, B59630, AD, and KB, were increased in the presence of sodium azide, suggesting that fluconazole resistance in these strains may be associated with an energy-dependent drug efflux. Fluconazole-resistant C. albicans strains all contained elevated amounts (2- to 17-fold) of mRNA encoding Cdr1, and an ATP-binding cassette-type transporter. In addition, C. albicans FR2 also contained increased amounts of mRNA encoding Benr, a major facilitator superfamily transporter. These results suggest that fluconazole enters C. albicans cells by facilitated diffusion and that fluconazole resistance may involve energy-dependent drug efflux associated with increased expression of Benr and/or Cdr1.

Antifungal Agents↗
PubMed1997

Modulation of the metabolism of beta-L-(-)-2',3'-dideoxy-3'-thiacytidine by thymidine, fludarabine, and nitrobenzylthioinosine.

beta-L-(-)-2',3'-Dideoxy-3'-thiacytidine (3TC) is a cytosine nucleoside analog that potently inhibits the replication of human and duck hepatitis B viruses and human immunodeficiency virus through the activity of its 5'-triphosphate ester metabolite. The present study examined the intracellular decay of 3TC 5'-phosphates and tested strategies for modulating the cellular content of those nucleotides in primary cultures of duck hepatocytes and in human hepatoma 2.2.15 cells and CCRF-CEM T lymphoblasts. Inhibition by deoxycytidine of the 5'-phosphorylation of 3TC in duck hepatocytes confirmed that, as in mammalian cells, deoxycytidine kinase catalyzed 3TC activation. The 5'-mono, 5'-di-, and 5'-triphosphates of 3TC underwent monoexponential elimination from duck hepatocytes and 2.2.15 cells (half-lives, 3.6 to 8.0 h). Thymidine and fludarabine, which are agents that enhance the activity of deoxycytidine kinase, were tested in strategies for increasing the cellular content of 3TC 5'-phosphates. Coordinate treatment of cells with 3TC and thymidine (50 microM) increased the content of 3TC 5'-monophosphate in duck hepatocytes and the content of 3TC 5'-di- and 5'-triphosphates in 2.2.15 cells, but enhancement of 3TC 5'-phosphate levels in CCRF-CEM cells required a higher thymidine concentration (100 microM). Fludarabine (5 microM) did not affect the contents of 3TC 5'-di- and 5'-triphosphates in duck hepatocytes, but modestly increased the contents of those nucleotides in 2.2.15 cells and CCRF-CEM cells. Nitrobenzylthioinosine (NBMPR), an inhibitor of the es facilitated diffusion nucleoside transporter, reduced the level of entry of 3TC into 2.2.15 cells and abolished inward fluxes of thymidine, adenosine, and deoxycytidine. In 2.2.15 cells and CCRF-CEM cells, NBMPR reduced the formation of 3TC 5'-di- and 5'-triphosphates and reversed the thymidine- and fludarabine-induced increases in the formation of those nucleotides. NBMPR protected against the cytotoxicity of 3TC in CCRF-CEM cells, whereas thymidine potentiated that toxicity, apparently by enhancing the formation of 3TC 5'-triphosphate. Taken together, these results indicate that deoxycytidine kinase and the es nucleoside transporter are targets for manipulation of the metabolism and activity of 3TC.

Affinity Labels↗
PubMed1985

d-Glucose Transport System of Zymomonas mobilis.

The properties of the d-glucose transport system of Zymomonas mobilis were determined by measuring the uptake of nonmetabolizable analogs (2-deoxy-d-glucose and d-xylose) by wild-type cells and the uptake of d-glucose itself by a mutant lacking glucokinase. d-Glucose was transported by a constitutive, stereospecific, carrier-mediated facilitated diffusion system, whereby its intracellular concentration quickly reached a plateau close to but not above the external concentration. d-Xylose was transported by the d-glucose system, as evidenced by inhibition of its uptake by d-glucose. d-Fructose was not an efficient competitive inhibitor of d-glucose uptake, indicating that it has a low affinity for the d-glucose transport system. The apparent K(m) of d-glucose transport was in the range of 5 to 15 mM, with a V(max) of 200 to 300 nmol min mg of protein. The K(m) of Z. mobilis glucokinase (0.25 to 0.4 mM) was 1 order of magnitude lower than the K(m) for d-glucose transport, although the V(max) values for transport and phosphorylation were similar. Thus, glucose transport cannot be expected to be rate limiting at concentrations of extracellular glucose normally used in fermentation processes, which greatly exceed the K(m) for the transport system. The low-affinity, high-velocity, nonconcentrative system for d-glucose transport described here is consistent with the natural occurrence of Z. mobilis in high-sugar environments and with the capacity of Z. mobilis for rapid conversion of glucose to metabolic products with low energetic yield.

Journal Article↗
PubMed1989

Competition for glucose between the yeasts Saccharomyces cerevisiae and Candida utilis.

The competition between the yeasts Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621 for glucose was studied in sugar-limited chemostat cultures. Under aerobic conditions, C. utilis always successfully completed against S. cerevisiae. Only under anaerobic conditions did S. cerevisiae become the dominant species. The rationale behind these observations probably is that under aerobic glucose-limited conditions, high-affinity glucose/proton symporters are present in C. utilis, whereas in S. cerevisiae, glucose transport occurs via facilitated diffusion with low-affinity carriers. Our results explain the frequent occurrence of infections by Crabtree-negative yeasts during bakers' yeast production.

Aerobiosis↗
PubMed1991

Low- and high-affinity transport systems for citric acid in the yeast Candida utilis.

Citric acid-grown cells of the yeast Candida utilis induced two transport systems for citric acid, presumably a proton symport and a facilitated diffusion system for the charged and the undissociated forms of the acid, respectively. Both systems could be observed simultaneously when the transport was measured at 25 degrees C with labelled citric acid at pH 3.5 with the following kinetic parameters: for the low-affinity system, Vmax, 1.14 nmol of undissociated citric acid s-1 mg (dry weight) of cells-1, and Km, 0.59 mM undissociated acid; for the high-affinity system, Vmax, 0.38 nmol of citrate s-1 mg (dry weight) of cells-1, and Km, 0.056 mM citrate. At high pH values (above 5.0), the low-affinity system was absent or not measurable. The two transport systems exhibited different substrate specificities. Isocitric acid was a competitive inhibitor of citric acid for the high-affinity system, suggesting that these tricarboxylic acids used the same transport system, while aconitic, tricarballylic, trimesic, and hemimellitic acids were not competitive inhibitors. With respect to the low-affinity system, isocitric acid, L-lactic acid, and L-malic acid were competitive inhibitors, suggesting that all of these mono-, di-, and tricarboxylic acids used the same low-affinity transport system. The two transport systems were repressed by glucose, and as a consequence diauxic growth was observed. Both systems were inducible, and not only citric acid but also lactic acid and malic acid may induce those transport systems. The induction of both systems was not dependent on the relative concentration of the anionic form(s) and of undissociated citric acid in the culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport↗
PubMed1993

Uncoupler-Resistant Glucose Uptake by the Thermophilic Glycolytic Anaerobe Thermoanaerobacter thermosulfuricus (Clostridium thermohydrosulfuricum).

The transport of glucose across the bacterial cell membrane of Thermoanaerobacter thermosulfuricus (Clostridium thermohydrosulfuricum) Rt8.B1 was governed by a permease which did not catalyze concomitant substrate transport and phosphorylation and thus was not a phosphoenolpyruvate-dependent phosphotransferase. Glucose uptake was carrier mediated, could not be driven by an artificial membrane potential (Deltapsi) in the presence or absence of sodium, and was not sensitive to inhibitors which dissipate the proton motive force (Deltap; tetrachlorosalicylanilide, N,N-dicyclohexylcarboiimide, and 2,4-dinitrophenol), and no uptake of the nonmetabolizable analog 2-deoxyglucose could be demonstrated. The glucokinase apparent K(m) for glucose (0.21 mM) was similar to the K(t) (affinity constant) for glucose uptake (0.15 mM), suggesting that glucokinase controls the rate of glucose uptake. Inhibitors of ATP synthesis (iodoacetate and sodium fluoride) also inhibited glucose uptake, and this effect was due to a reduction in the level of ATP available to glucokinase for glucose phosphorylation. These results indicated that T. thermosulfuricus Rt8.B1 lacks a concentrative uptake system for glucose and that uptake is via facilitated diffusion, followed by ATP-dependent phosphorylation by glucokinase. In T. thermosulfuricus Rt8.B1, glucose is metabolized by the Embden-Meyerhof-Parnas pathway, which yields 2 mol of ATP (G. M. Cook, unpublished data). Since only 1 mol of ATP is used to transport 1 mol of glucose, the energetics of this system are therefore similar to those found in bacteria which possess a phosphotransferase.

Journal Article↗
PubMed1993

Energetics and kinetics of maltose transport in Saccharomyces cerevisiae: a continuous culture study.

In Saccharomyces cerevisiae, maltose is transported by a proton symport mechanism, whereas glucose transport occurs via facilitated diffusion. The energy requirement for maltose transport was evaluated with a metabolic model based on an experimental value of YATP for growth on glucose and an ATP requirement for maltose transport of 1 mol.mol-1. The predictions of the model were verified experimentally with anaerobic, sugar-limited chemostat cultures growing on a range of maltose-glucose mixtures at a fixed dilution rate of 0.1 h-1. The biomass yield (grams of cells.gram of sugar-1) decreased linearly with increasing amounts of maltose in the mixture. The yield was 25% lower during growth on maltose than during that on glucose, in agreement with the model predictions. During sugar-limited growth, the residual concentrations of maltose and glucose in the culture increased in proportion to their relative concentrations in the medium feed. From the residual maltose concentration, the in situ rates of maltose consumption by cultures, and the Km of the maltose carrier for maltose, it was calculated that the amount of this carrier was proportional to the in situ maltose consumption rate. This was also found for the amount of intracellular maltose. These two maltose-specific enzymes therefore exert high control over the maltose flux in S. cerevisiae in anaerobic, sugar-limited, steady-state cultures.

Adenosine Triphosphate↗
PubMed1996

Development of an arabinose-fermenting Zymomonas mobilis strain by metabolic pathway engineering.

The substrate fermentation range of the ethanologenic bacterium Zymomonas mobilis was expanded to include the pentose sugar, L-arabinose, which is commonly found in agricultural residues and other lignocellulosic biomass. Five genes, encoding L-arabinose isomerase (araA), L-ribulokinase (araB), L-ribulose-5-phosphate-4-epimerase (araD), transaldolase (talB), and transketolase (tktA), were isolated from Escherichia coli and introduced into Z. mobilis under the control of constitutive promoters that permitted their expression even in the presence of glucose. The engineered strain grew on and produced ethanol from L-arabinose as a sole C source at 98% of the maximum theoretical ethanol yield, based on the amount of consumed sugar. This indicates that arabinose was metabolized almost exclusively to ethanol as the sole fermentation product, with little by-product formation. Although no diauxic growth pattern was evident, the microorganism preferentially utilized glucose before arabinose, apparently reflecting the specificity of the indigenous facilitated diffusion transport system. This microorganism may be useful, along with the previously developed xylose-fermenting Z. mobilis (M. Zhang, C. Eddy, K. Deanda, M. Finkelstein, and S. Picataggio, Science 267:240-243, 1995), in a mixed culture for efficient fermentation of the predominant hexose and pentose sugars in agricultural residues and other lignocellulosic feedstocks to ethanol.

Arabinose↗
PubMed1997

Kinetics of Sugar Transport and Phosphorylation Influence Glucose and Fructose Cometabolism by Zymomonas mobilis.

The competitive inhibition of fructokinase by glucose has been proposed as the mechanism by which Zymomonas mobilis preferentially consumes glucose from mixtures of glucose and fructose and accumulates fructose when growing on sucrose. In this study, incorporation of radioactive fructose into biomass was used as a measure of fructose catabolism. It was determined that the rate of fructose incorporation by Z. mobilis CP4 was somewhat lower in the presence of an equimolar concentration of glucose but that the inhibition of fructokinase by glucose was not nearly as severe in vivo as was predicted from in vitro studies. Interestingly, addition of glucose to a culture of Z. mobilis CP4-M2, a glucokinaseless mutant, resulted in an immediate and nearly complete inhibition of fructose incorporation. Furthermore, addition of nonmetabolizeable glucose analogs had a similar effect on fructose catabolism by the wild-type Z. mobilis CP4, and fructose uptake by Z. mobilis CP4-M2 was shown to be severely inhibited by equimolar amounts of glucose. These results suggest that competition for fructose transport plays an important role in preferential catabolism of glucose from sugar mixtures. Indeed, the apparent K(infm) values for sugar uptake by Z. mobilis CP4 were approximately 200 mM for fructose and 13 mM for glucose. Other experiments supported the conclusion that a single facilitated diffusion transport system, encoded by the glf gene, is solely responsible for the uptake of both glucose and fructose. The results are discussed with regard to the hypothesis that the kinetics of sugar transport and phosphorylation allow the preferential consumption of glucose and accumulation of fructose, making the fructose available for the enzyme glucose-fructose oxidoreductase, which forms sorbitol, an important osmoprotectant for Z. mobilis when growing in the presence of high sugar concentrations.

Journal Article↗
PubMed1999

Transport and utilization of hexoses and pentoses in the halotolerant yeast Debaryomyces hansenii.

Debaryomyces hansenii is a yeast species that is known for its halotolerance. This organism has seldom been mentioned as a pentose consumer. In the present work, a strain of this species was investigated with respect to the utilization of pentoses and hexoses in mixtures and as single carbon sources. Growth parameters were calculated for batch aerobic cultures containing pentoses, hexoses, and mixtures of both types of sugars. Growth on pentoses was slower than growth on hexoses, but the values obtained for biomass yields were very similar with the two types of sugars. Furthermore, when mixtures of two sugars were used, a preference for one carbon source did not inhibit consumption of the other. Glucose and xylose were transported by cells grown on glucose via a specific low-affinity facilitated diffusion system. Cells derepressed by growth on xylose had two distinct high-affinity transport systems for glucose and xylose. The sensitivity of labeled glucose and xylose transport to dissipation of the transmembrane proton gradient by the protonophore carbonyl cyanide m-chlorophenylhydrazone allowed us to consider these transport systems as proton symports, although the cells displayed sugar-associated proton uptake exclusively in the presence of NaCl or KCl. When the V(max) values of transport systems for glucose and xylose were compared with glucose- and xylose-specific consumption rates during growth on either sugar, it appeared that transport did not limit the growth rate.

Biological Transport, Active↗
PubMed2001

A large gene cluster encoding several magnetosome proteins is conserved in different species of magnetotactic bacteria.

In magnetotactic bacteria, a number of specific proteins are associated with the magnetosome membrane (MM) and may have a crucial role in magnetite biomineralization. We have cloned and sequenced the genes of several of these polypeptides in the magnetotactic bacterium Magnetospirillum gryphiswaldense that could be assigned to two different genomic regions. Except for mamA, none of these genes have been previously reported to be related to magnetosome formation. Homologous genes were found in the genome sequences of M. magnetotacticum and magnetic coccus strain MC-1. The MM proteins identified display homology to tetratricopeptide repeat proteins (MamA), cation diffusion facilitators (MamB), and HtrA-like serine proteases (MamE) or bear no similarity to known proteins (MamC and MamD). A major gene cluster containing several magnetosome genes (including mamA and mamB) was found to be conserved in all three of the strains investigated. The mamAB cluster also contains additional genes that have no known homologs in any nonmagnetic organism, suggesting a specific role in magnetosome formation.

Amino Acid Sequence↗
PubMed1974

Augmentation of glucose transport in macrophages after particle ingestion.

Guinea pig and mouse peritoneal macrophages in culture transport glucose by a specific, saturable system with characteristics compatible with facilitated diffusion. Phagocytosis of killed staphylococci or polystyrene latex spheres results in a significant increase in uptake of 2-deoxy-d-glucose. Reciprocal plot analysis showed that the K(m) values were lowered as a consequence of phagocytosis by a factor of between 2 and 3 in both cell types; V(max) values were not significantly changed. The nature of the intracellular sugar pool was analyzed and found to consist of free and phosphorylated 2-deoxy-d-glucose at a relatively constant ratio of 1:2 after periods of uptake between 1 and 20 min. Phagocytosis resulted in increased levels of both free and phosphorylated sugars in the cytoplasm. Since the K(m) values were lowered, augmented glucose uptake could not be accounted for by altered hexokinase activity. It was concluded that phagocytosis induces changes in the glucose transport system per se. The data are compatible with the metabolic changes known to be associated with particle ingestion by phagocytic cells. The mechanism by which glucose transport is augmented after loss of significant amounts of cell surface during the phagocytic process is not yet known.

Animals↗