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PubMedDate not supplied

Structural and dynamic properties of bacterial type IV secretion systems (review).

The type IV secretion systems (T4SS) are widely distributed among the gram-negative and -positive bacteria. These systems mediate the transfer of DNA and protein substrates across the cell envelope to bacterial or eukaryotic cells generally through a process requiring direct cell-to-cell contact. Bacteria have evolved T4SS for survival during establishment of pathogenic or symbiotic relationships with eukaryotic hosts. The Agrobacterium tumefaciens VirB/D4 T4SS and related conjugation machines serve as models for detailed mechanistic studies aimed at elucidating the nature of translocation signals, machine assembly pathways and architectures, and the dynamics of substrate translocation. The A. tumefaciens VirB/D4 T4SS are polar-localized organelles composed of a secretion channel and an extracellular T pilus. These T4SS are assembled from 11 or more subunits. whose membrane topologies, intersubunit contacts and, in some cases, 3-dimensional structures are known. Recently, powerful in vivo assays have identified C-terminal translocation signals, defined for the first time the translocation route for a DNA substrate through a type IV secretion channel, and supplied evidence that ATP energy consumption contributes to a late stage of machine morphogenesis. Together, these recent findings describe the mechanics of type IV secretion in unprecedented detail.

Adenosine Triphosphate↗
PubMedDate not supplied

Mitochondrial nitric-oxide synthase: role in pathophysiology.

The biochemistry of the mitochondrial production of nitric oxide is reviewed to gain insight into the basic role of this radical in mitochondrial and cellular oxidative metabolism. The mitochondrial production of nitric oxide is catalyzed by a nitric-oxide synthase (mtNOS). This enzyme has the same cofactor and substrate requirements as other constitutive nitric-oxide synthases. Its occurrence was demonstrated in various mitochondrial preparations from different organs and species using diverse approaches (oxidation of oxymyoglobin, electron paramagnetic resonance in conjunction with spin trap, radiolabeled L-arginine, immunohistochemistry, nitric-oxide electrode). MtNOS has been identified as the alpha isoform of nNOS, acylated at a Thr or Ser residue, and phosphorylated at the C-terminal end. Endogenous nitric oxide reversibly inhibits oxygen consumption and ATP synthesis by competitive inhibition of cytochrome oxidase. Nitric oxide is the first molecule that fulfills the requirement for a cytochrome oxidase activity modulator: it is a competitive inhibitor, produced endogenously at a fair rate near the target site, at concentrations high enough to exhibit an inhibitory effect on cytochrome oxidase. The role of the mitochondrial nitric oxide production is discussed in terms of the physiological (modulating oxygen gradients into tissues) and pathological (abrogation of oxygen gradient modification, apoptosis, protein nitrative/oxidative stress) implications.

Animals↗
PubMed1979

Histidine mutants requiring adenine: selection of mutants with reduced hisG expression in Salmonella typhimurium.

A method is described for the selection of Salmonella typhimurium mutants with reduced levels of hisG enzyme activity. This method is based on the fact that the hisG enzyme catalyzes the consumption of ATP in the first step of histidine biosynthesis. Normally, this reaction is closely regulated, both by feedback inhibition and by repression of the operon. However, conditions can be set up that result in the uncontrolled use of adenine in histidine biosynthesis. Cells grown under these conditions become phenotypic adenine auxotrophs. Some revertant clones that no longer require adenine contain mutations in hisG, hisE, or the his-control region. The hisG mutations are of all types (nonsense, frameshift, missense, deletion and leady types), and they map throughout the hisG gene.

ATP Phosphoribosyltransferase↗
PubMed2004

Transcription regulation of TNF-alpha-early response genes by poly(ADP-ribose) polymerase-1 in murine heart endothelial cells.

Poly(ADP-ribose) polymerase-1 (PARP-1) has been involved in endothelial cell dysfunction associated with various pathophysiological conditions. The intrinsic mechanism of PARP-1-mediated endothelial cell dysfunction could be related to PARP-1 overactivation, NAD(+) consumption and ATP depletion. An alternative way could involve transcription regulation. By using high-density microarrays, we examined early tumor necrosis factor alpha (TNF-alpha)-stimulated gene expression profiles in PARP-1(+/+) and PARP-1(-/-) murine heart endothelial cells. TNF-alpha modulated a significant number of genes in both cell types. We have identified a set of genes whose expression in response to TNF-alpha is modulated by PARP-1, whereas the expression of others is PARP-1-independent. Up-regulation of several genes involved in the inflammatory response is hampered in the absence of PARP-1. Moreover, NF-kappaB-dependent transcriptional activation is partially inhibited in PARP-1(-/-) compared to PARP-1(+/+) cells. However, we found that PARP-1 might also silence transcription of several NF-kappaB target genes. Overall, our results show that PARP-1 is regulating the expression of genes by the endothelial cells both in a positive and a negative fashion, with the final effects depending on the gene. Individual studies of these genes are now necessary to clarify the intrinsic mechanism by which PARP-1 is controlling transcription and thereby finding out different therapeutic approaches involving PARP-1.

Animals↗
PubMed2000

Triiodothyronine-mediated up-regulation of UCP2 and UCP3 mRNA expression in human skeletal muscle without coordinated induction of mitochondrial respiratory chain genes.

Triiodothyronine (T3) increases mitochondrial respiration and promotes the uncoupling between oxygen consumption and ATP synthesis. T3 effect is mediated partly through transcriptional control of genes encoding mitochondrial proteins. We determined the effect of T3 on mRNA levels of uncoupling proteins (UCP) and proteins involved in the biogenesis of the respiratory chain in human skeletal muscle and on UCP2 mRNA expression in adipose tissue. Ten young, healthy males received 75 to 100 5g of T3 per day for 14 days. The increase in plasma-free T3 levels was associated with an increase of resting metabolic rate and a decrease of respiratory quotient. In skeletal muscle, treatment with T3 induced a twofold increase of both UCP2 and UCP3 mRNA levels (p c oxidase subunits 2 and 4, nuclear respiratory factor 1, mitochondrial transcription factor A, and the co-activator PGC1 did not change during the treatment. In adipose tissue, UCP2 mRNA levels increased threefold. The direct effect of T3 on skeletal muscle an d adipose tissue UCP2 and UCP3 mRNA expression was demonstrated in vitro in human primary cultures. Our data show that T3 induces UCP2 and UCP3 mRNA expression in humans. In skeletal muscle, UCP regulation by T3 is not associated with the transcriptional regulation of respiratory chain proteins.

Adipose Tissue↗
PubMed2006

Inhibition of phospholipase C attenuates liver mitochondrial calcium overload following cold ischemia.

BACKGROUND: Graft failure due to cold ischemia (CI) injury remains a significant problem during liver transplantation. During CI, the consumption of ATP and the increase in cellular Ca concentration may result in mitochondrial Ca (mCa) overload through the mCa uniporter, which can ultimately lead to apoptosis and graft nonfunction. We recently identified phospholipase C-dl (PLC-dl) as a novel regulator of mCa uptake in the liver, and now extend those studies to examine the role of mitochondrial PLC in liver CI injury. METHODS: Rat livers were perfused with University of Wisconsin (UW) solution. Half was homogenized immediately; the other half was cold-stored for 24 hr in UW. Mitochondria were extracted by differential centrifugation and incubated in buffer containing ATP and 0.1 or 0.2 microM Ca. The selective PLC inhibitor, U-73122, was added to determine the effects of PLC inhibition on mCa uptake following CI. Western blots and densitometry quantified mitochondrial PLC expression. Mito Tracker Red fluorescence microscopy was used to verify mitochondrial transmembrane potential. RESULTS: Twenty-four hour CI caused a significant increase in mCa uptake (P<0.001), and increasing extramitochondrial Ca potentiated this effect. The PLC inhibitor, U-73122, decreased mCa uptake in nonischemic mitochondria (P<0.001), and had a greater effect on CI mitochondria (P<0.001). Mitochondrial PLC-dl expression increased 175+/-75% following CI (P<0.05). CONCLUSIONS: These data demonstrate that PLC-dl is essential for mCa uptake following CI, and that the PLC pathway may be sensitized by CI. The CI-induced increase in mitochondrial PLC-delta1 expression represents a novel mechanism whereby mCa uptake can increase independently of cytosolic conditions.

Adenosine Triphosphate↗
PubMed1998

Inactivation of the Kluyveromyces lactis KlPDA1 gene leads to loss of pyruvate dehydrogenase activity, impairs growth on glucose and triggers aerobic alcoholic fermentation.

The KlPDA1 gene, encoding the E1alpha subunit of the mitochondrial pyruvate-dehydrogenase (PDH) complex was isolated from a Kluyveromyces lactis genomic library by screening with a 1.1 kb internal fragment of the Saccharomyces cerevisiae PDA1 gene. The predicted amino acid sequence encoded by KlPDA1 showed 87% similarity and 79% identity to its S. cerevisiae counterpart. Disruption of KIPDA1 resulted in complete absence of PDH activity in cell extracts. The maximum specific growth rate on glucose of null mutants was 3.5-fold lower than that of the wild-type, whereas growth on ethanol was unaffected. Wild-type K. lactis CBS 2359 exhibits a Crabtree-negative phenotype, i.e. no ethanol was produced in aerobic batch cultures grown on glucose. In contrast, substantial amounts of ethanol and acetaldehyde were produced in aerobic cultures of an isogenic Klpda1 null mutant. A wild-type specific growth rate was restored after introduction of an intact KlPDA1 gene but not, as previously found for S. cerevisiae pda1 mutants, by cultivation in the presence of leucine. The occurrence of aerobic fermentation and slow growth of the Klpda1 null mutant indicate that, although present, the enzymes of the PDH bypass (pyruvate decarboxylase, acetaldehyde dehydrogenase and acetyl-CoA synthetase) could not efficiently replace the PDH complex during batch cultivation on glucose. Only at relatively low growth rates (D = 0.10 h(-1)) in aerobic, glucose-limited chemostat cultures, could the PDH bypass completely replace the PDH complex, thus allowing fully respiratory growth. This resulted in a lower biomass yield [g biomass (g glucose)-1] than in the wild-type due to a higher consumption of ATP in the PDH bypass compared to the formation of acetyl-CoA via the PDH complex.

Aerobiosis↗
PubMed1990

The S-Methylmethionine Cycle in Lemna paucicostata.

The metabolism of S-methylmethionine has been studied in cultures of plants of Lemna paucicostata and of cells of carrot (Daucus carota) and soybean (Glycine max). In each system, radiolabeled S-methylmethionine was rapidly formed from labeled l-methionine, consistent with the action of S-adenosyl-l-methionine:methionine S-methyltransferase, an enzyme which was demonstrated during these studies in Lemna homogenates. In Lemna plants and carrot cells radiolabel disappeared rapidly from S-methylmethionine during chase incubations in nonradioactive media. The results of pulse-chase experiments with Lemna strongly suggest that administered radiolabeled S-methylmethionine is metabolized initially to soluble methionine, then to the variety of compounds formed from soluble methionine. An enzyme catalyzing the transfer of a methyl group from S-methylmethionine to homocysteine to form methionine was demonstrated in homogenates of Lemna. The net result of these reactions, together with the hydrolysis of S-adenosylhomocysteine to homocysteine and adenosine, is to convert S-adenosylmethionine to methionine and adenosine. A physiological advantage is postulated for this sequence in that it provides the plant with a means of sustaining the pool of soluble methionine even when overshoot occurs in the conversion of soluble methionine to S-adenosylmethionine. The facts that the pool of soluble methionine is normally very small relative to the flux into S-adenosylmethionine and that the demand for the latter compound may change very markedly under different growth conditions make it plausible that such overshoot may occur unless the rate of synthesis of S-adenosylmethionine is regulated with exquisite precision. The metabolic cost of this apparent safeguard is the consumption of ATP. This S-methylmethionine cycle may well function in plants other than Lemna, but further substantiating evidence is neeeded.

Journal Article↗
PubMed1999

Crystal structure of brain-type creatine kinase at 1.41 A resolution.

Excitable cells and tissues like muscle or brain show a highly fluctuating consumption of ATP, which is efficiently regenerated from a large pool of phosphocreatine by the enzyme creatine kinase (CK). The enzyme exists in tissue--as well as compartment-specific isoforms. Numerous pathologies are related to the CK system: CK is found to be overexpressed in a wide range of solid tumors, whereas functional impairment of CK leads to a deterioration in energy metabolism, which is phenotypic for many neurodegenerative and age-related diseases. The crystal structure of chicken cytosolic brain-type creatine kinase (BB-CK) has been solved to 1.41 A resolution by molecular replacement. It represents the most accurately determined structure in the family of guanidino kinases. Except for the N-terminal region (2-12), the structures of both monomers in the biological dimer are very similar and closely resemble those of the other known structures in the family. Specific Ca2+-mediated interactions, found between two dimers in the asymmetric unit, result in structurally independent heterodimers differing in their N-terminal conformation and secondary structure. The high-resolution structure of BB-CK presented in this work will assist in designing new experiments to reveal the molecular basis of the multiple isoform-specific properties of CK, especially regarding different subcellular locations and functional interactions with other proteins. The rather similar fold shared by all known guanidino kinase structures suggests a model for the transition state complex of BB-CK analogous to the one of arginine kinase (AK). Accordingly, we have modeled a putative conformation of CK in the transition state that requires a rigid body movement of the entire N-terminal domain by rms 4 A from the structure without substrates.

Adenosine Triphosphate↗
PubMed1984

Effects of homologous plasma cross-circulation on liver function in galactosamine-induced hepatic necrosis in rats.

Plasma cross-circulation that resembles clinical plasma exchange was carried out in rats with galactosamine (GalN)-treated hepatic failure to investigate its effect on the damaged liver function. Twenty-four hours after the injection of GalN, plasma cross-circulation was performed at a plasma flow rate of 0.1 ml/min for 6 h. At 48 h after the injection of GalN, survival was obtained in 6 of 8 GalN-injected rats treated with plasma cross-circulation as compared with 4 of 10 GalN-injected rats treated with sham circulation. State 3 oxygen consumption and ATP synthesis (mitochondrial respiratory function) and ATP, ADP, and total adenine nucleotide contents in the liver were significantly higher in the former group than in the latter group at that period, as determined by sacrificing the surviving animals. Although the survival rate was not significantly improved, evidence suggests that plasma cross-circulation enhanced mitochondrial phosphorylative activity and produced an augmented high-energy state of the liver, which had been markedly reduced by GalN administration. An efficient removal of toxic metabolites as well as an influx of a large amount of fresh plasma by plasma cross-circulation would be beneficial for the regenerative process of the necrosing liver tissues.

Adenine Nucleotides↗
PubMed2004

Yersinia enterocolitica type III secretion depends on the proton motive force but not on the flagellar motor components MotA and MotB.

The flagellum is believed to be the common ancestor of all type III secretion systems (TTSSs). In Yersinia enterocolitica, expression of the flagellar TTSS and the Ysc (Yop secretion) TTSS are inversely regulated. We therefore hypothesized that the Ysc TTSS may adopt flagellar motor components in order to use the pathogenicity-related translocon in a drill-like manner. As a prerequisite for this hypothesis, we first tested a requirement for the proton motive force by both systems using the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP). Motility as well as type III-dependent secretion of Yop proteins was inhibited by CCCP. We deleted motAB, which resulted in an immotile phenotype. This mutant, however, secreted amounts of Yops to the supernatant comparable to those of the wild type. Translocation of Yops into host cells was also not affected by the motAB deletion. Virulence of the mutant was comparable to that of the wild type in the mouse oral infection model. Thus, the hypothesis that the Ysc TTSS might adopt flagellar motor components was not confirmed. The finding that, in addition to consumption of ATP, Ysc TTSS requires the proton motive force is discussed.

Animals↗
PubMed1974

Physiological studies of Bacillus subtilis minicells.

Minicells produced by Bacillus subtilis strains carrying the div IV-B1 mutation, (CU 403 div IV-B1 and CU 403 div IV-B1, tag-1), were purified by a procedure which destroys parental cells with ultrasound, but spares minicells. Such preparations generally contain 10(9) or more minicells/ml and less than 10(4) colony-forming units/ml. Purified minicells are resistant to autolysis in tris(hydroxymethyl)aminomethane buffer, pH 7.5, at 30 C, conditions which result in total lysis of parental cells. Minicells are not completely devoid of autolytic activity, however. The medium in which minicells are produced, the temperature at which purified minicells are incubated, and the genotype of cells from which the minicells are derived all influence the rate of autolysis of purified minicells. These parameters are demonstrated by using minicells obtained from div IV-B1 and div IV-B1, tag-1 strains. Ultrastructural differences have been observed in the products of autolysis of these two minicell strains. Minicells are sensitive to low levels of lysozyme and yield miniprotoplasts when the wall is removed in an osmotically protective environment. Although minicells are unable to grow, they can maintain their integrity over long periods of time, which suggests functional energy metabolism in minicells. Direct measurements of adenosine 5'-triphosphate (ATP) levels by the luciferase assay indicated that minicells can produce ATP. Oxygen consumption, measured by standard respirometry techniques, also indicates functional metabolism in minicells. These findings demonstrate that minicells purified by ultrasound are suitable material for study of physiological processes in anucleate cells.

Adenosine Triphosphate↗
PubMed1982

Release of endogenous noradrenaline from the rat tail artery induced by veratridine.

The overflow of endogenous noradrenaline from the isolated rat tail artery was measured using a radioenzymatic method. Veratridine increased the overflow markedly even in the absence of external Ca2+. Modifications of the effect of 5 microM veratridine by tetrodotoxin, pargyline, cocaine, lidocaine, and phenoxybenzamine indicated that interaction of the alkaloid with the sodium channel induces primarily nonexocytotic release of noradrenaline. Ouabain inhibited the effect of 5 microM veratridine on the overflow into Ca2+-free solution, but it greatly potentiated the effect if external Ca2+ was present. Potentiation of the effect of veratridine in Ca2+-free solution by cyanide was ouabain sensitive. These observations are consistent with the hypothesis that, at low concentrations of veratridine such as 5 microM, the initial cause of enhanced release of noradrenaline may be a consequence of increased activity of the sodium pump, namely increased consumption of ATP by the pump.

Adenosine Triphosphate↗
PubMed2004

Inhibition of epidermal growth factor receptor signaling protects human malignant glioma cells from hypoxia-induced cell death.

Epidermal growth factor receptor (EGFR) signaling has become an important target for drug development because EGFR signaling enhances tumor cell proliferation, migration, and invasion and inhibits apoptosis. However, the results of clinical trials using EGFR inhibitors in patients with solid tumors have been disappointing. Here, we report a protective effect of the EGFR inhibitors AG1478 and PD153035 against cell death induced by acute hypoxia, which contrasts with their proapoptotic effects under normoxia. Under hypoxic conditions, both agents reduced glucose consumption, delayed ATP depletion, and preserved the mitochondrial membrane potential. Exposure either to hypoxia or the EGFR inhibitors under normoxic conditions resulted in the dephosphorylation of ribosomal protein S6, a player in the energy and nutrient-sensing pathway governed by mammalian target-of-rapamycin (mTOR). Combined inhibition of phosphatidylinositol 3'-kinase (PI3K) and extracellular signal-regulated kinase-1/2 (ERK1/2) mimicked the protective effects of EGFR inhibition on hypoxia-induced cell death and protein S6 dephosphorylation. These results caution that therapies targeting EGFR signaling pathways can protect tumor cells from acute hypoxia.

Adenosine Triphosphate↗
PubMed2004

Contribution of glutamine synthetase to ammonia-induced apoptosis in gastric mucosal cells.

BACKGROUND/AIMS: Glutamine synthetase is a key enzyme necessary for ammonia detoxification in the brain, but excessive activation of this enzyme can be cytotoxic to neural cells as a consequence of excessive consumption of ATP and glutamate. The stomach also expresses high levels of glutamine synthetase and this study aimed to investigate a possible pathophysiological role of glutamine synthetase in ammonia-induced gastric mucosal injury. METHODS: Normal rat gastric mucosal epithelial (RGM-1) cells were treated with ammonia, and a specific glutamine synthetase inhibitor (methionine sulfoximine) was used to assess the action of glutamine synthetase. RESULTS: Treatment with ammonia induced apoptotic cell death. Increased expression of p21 and Bax, decreased expression of Bcl-2, cytochrome C release from the mitochondria into the cytosol and subsequent activation of caspase-9 and -3 were identified in the cells treated with ammonia, although there was no apparent change in p53 expression. On the other hand, pretreatment with various concentrations of methionine sulfoximine reduced the glutamine synthetase activity in ammonia-treated RGM-1 cells, and prevented the induction of apoptosis and the reduction in intracellular ATP levels in a dose-dependent manner. CONCLUSIONS: Our results suggested that the energy exhaustion which resulted from an overload of ammonia to glutamine synthetase may have initiated the apoptotic signaling in gastric mucosal cells.

Adenosine Triphosphate↗
PubMed1996

Linkage of aerobic glycolysis to sodium-potassium transport in rat skeletal muscle. Implications for increased muscle lactate production in sepsis.

Although a linkage between aerobic glycolysis and sodium-potassium transport has been demonstrated in diaphragm, vascular smooth muscle, and other cells, it is not known whether this linkage occurs in skeletal muscle generally. Metabolism of intact hind-leg muscles from young rats was studied in vitro under aerobic incubation conditions. When sodium influx into rat extensor digitorum longus (EDL) and soleus muscles was facilitated by the sodium ionophore monensin, muscle weight gain and production of lactate and alanine were markedly stimulated in a dose-dependent manner. Although lactate production rose in both muscles, it was more pronounced in EDL than in soleus. Monensin-induced lactate production was inhibited by ouabain or by incubation in sodium-free medium. Preincubation in potassium-free medium followed by potassium re-addition also stimulated ouabain-inhibitable lactate release. Replacement of glucose in the incubation medium with pyruvate abolished monensin-induced lactate production but exacerbated monensin-induced weight gain. Muscles from septic or endotoxin-treated rats exhibited an increased rate of lactate production in vitro that was partially inhibited by ouabain. Increases muscle lactate production in sepsis may reflect linked increases in activity of the Na+, K+-ATPase, consumption of ATP and stimulation of aerobic glycolysis.

Aerobiosis↗
PubMed1998

Unmasking of a periodic Na+ entry into glucose-stimulated pancreatic beta-cells after partial inhibition of the Na/K pump.

The cytoplasmic concentration of Na+ ([Na+]i) was measured in individual mouse beta-cells using dual wavelength microfluorometry and the indicator sodium-binding benzofuran isophtalate. Under conditions known to induce large amplitude oscillations in cytoplasmic Ca2+ (1.3 mM Ca2+; 11 mM glucose), [Na+]i remained low and stable at 10-14 mM. Partial suppression of the Na/K pump with 50 microM ouabain resulted in oscillations of [Na+]i in 65% of the cells (frequency, 0.13+/-O.O1 min(-l); amplitude, 4.4 +/-0.3 mM). The oscillations were unaffected by the presence of 3 microM tetrodotoxin, but disappeared when the medium was depleted of Ca2+ or supplemented with 10 microM methoxyverapamil. The analysis of the ouabain effect was facilitated by replacing extracellular Ca2+ with 5 mM Sr2+. In the Sr2+-containing medium, oscillations of [Na+]i were seen in more than 70% of the beta-cells exposed to 11 mM glucose. Ouabain (50 microM) modified the [Na+]i oscillations by increasing their amplitudes almost 3-fold and reducing the frequency from once every 3 min to once every 10 min. A relationship between oscillations of cytoplasmic Sr2+ and Na+ was apparent both from observations of similar frequencies and for the modifications obtained with ouabain. It is concluded that the glucose-induced oscillations of cytoplasmic Ca2+ result in a rhythmic entry of Na+, usually balanced by the Na/K pump. A resulting periodic consumption of ATP in the Na/K pump might have implications for the release of insulin by affecting ATP-dependent processes associated with the plasma membrane.

Animals↗
PubMed2006

Determination of p-glycoprotein ATPase activity using luciferase.

We investigated whether P-glycoprotein (P-gp) ATPase activity of Caco-2 cell membranes could be estimated by measuring consumption of ATP using luciferin-luciferase reaction, and whether the results would be useful for assessment of the interactions between P-gp and drugs. The vanadate-sensitive ATPase activity of Caco-2 cell membranes was measured rapidly with high sensitivity using luciferin-luciferase reaction. Cyclosporin A, verapamil, digoxin and quinidine stimulated the ATPase activity concentration-dependently with Km values of 5.3, 0.9, 1.2 and 4.1 microM, respectively. These values except for digoxin were comparable with previous reports. The ATPase activity and P-gp mRNA expression in Caco-2 cells were induced by all-trans-retinoic acid, digoxin and levothyroxine, but not dexamethasone or rifampicin. This method was useful to assess interactions with P-gp and drugs, and was used to elucidate the mechanisms of interaction of levothyroxine and digoxin.

ATP Binding Cassette Transporter, Subfamily B, Mem↗