Uptake and metabolism of thyroid hormones by cultured monkey hepatocarcinoma cells. Effects of potassium cyanide and dinitrophenol

Cultured monkey hepatocarcinoma cell (NCLP-6E) were used to investigate the uptake and metabolism of thyroid hormones. Intracellular accumulation was shown by the failure to acutely release hormone from cells subsequently exposed to serum proteins, and by the metabolic trnasformation of the hormones to deiodinated products and their sulfates. When hepatocarcinoma cell monolayers were studied at hormone concentrations below 10(-10) M, neither KCN nor dinitrophenol inhibited uptake. Taken together with previous findings that uptake was neither saturable nor reduced at low temperature, these results indicate that this process was not active transport. Deiodination of both the phenolic and non-phenolic rings, however, was partially inhibited by KCN but not by dinitrophenol. Sulfation of 3,3'-diiodothyronine and 3'-monoiodothyronine was strongly inhibited by both KCN and dinitrophenol. Uptake of the hormones and their metabolites was also measured in suspended hepatocarcinoma cells and compared with the uptake by normal rat hepatocytes, human fibroblasts and human lymphocytes. In these experiments 1 micrometer triidothyronine and 0.47 mM dinitrophenol were used to inhibit deiodination and sulfation, respectively. Uptake was similar in all cell types. Accumulation was highest with 3,5,3'-triiodothyronine, intermediate with other compounds having iodines in both rings, lowest with compounds iodinated in only one ring, and absent with iodothronine sulfates. These findings help to explain the relative rates of metabolism of the iodothyronines and their release from the cells.     

Characteristics of active transport of thyroid hormone into rat hepatocytes

Thyroid hormone uptake into primary cultured rat hepatocytes was studied using 1-min incubations with radio-iodine-labelled iodothyronines. (1) Uptake of thyroxine indicates two saturable sites apparent K_m values of 1.2 nM and 1.0 μM, and non-saturable uptake. Similar kinetics of triiodothyronine uptake have been observed. (2) The high-affinity systems of both hormones are energy-dependent (i.e., inhibited by KCN and oligomycin). It is postulated that these systems represent active transport of thyroid hormone into the cell. (3) Analysis of mutual inhibition by the substrates for the triiodothyronine and thyroxine transport systems indicates that triiodothyromine and thyroxine cross the cell membrane via separate transport systems. (4) Preincubation with ouabain resulted in a decrease in uptake of both triiodothyronine and thyroxine, suggesting that a sodium gradient is essential for this transport.     

Glucose transport in isolated prosthecae of Asticcacaulis biprosthecum.

Active transport of glucose in prosthecae isolated from cells of Asticcacaulis biprosthecum was stimulated by the non-physiological electron donor N, N, N', N'-tetramethyl-p-phenylenediamine dihydrochloride. Glucose uptake was mediated by two transport systems; the apparent Km of the high-affinity system was 1.8 muM and that of the low-affinity system was 34 muM. Free glucose accumulated within prosthecae at a concentration 60 to 200 times above that present externally, depending on the Km of the system being observed. The glucose transport system in prosthecae was stereospecific for D-glucose, and neither methyl alpha-D-glucopyranoside nor 2-deoxyglucose was transported. Uptake of glucose was inhibited by N-ethylmaleimide (NEM) and p-chloromercuribenzoate (PCMB), and the inhibition by PCMB but not by NEM was reversed by dithiothreitol. Glucose uptake was also inhibited by the uncoupling agents 5-chloro-3-t-butyl-2'-nitrosalicylanilide (S-13), 5-chloro-3-(p-chlorophenyl)-4'-chlorosalicylanilide (S-6), and carbonyl-cyanide m-chlorophenylhydrazone (CCCP) and by the respiratory inhibitor KCN. Efflux of glucose from preloaded prosthecae was induced by PCMB and KCN, but not by S-13 or CCCP. Glucose uptake was not affected by arsenate or an inhibitor of membrane-bound adenosine triphosphatases, N, N'-dicyclohexylcarbodiimide. The lack of inhibition by these two compounds, combined with the extremely low levels of adenosine 5'-triphosphate present in prosthecae, indicates that adenosine 5'-triphosphate is not involved in the transport of glucose by prosthecae.     

Studies on the mechanism of hrmonal stimulation of zinc uptake in human cell cultures: hormone-cell interactions and characteristics of zinc accumulation

Adrenal steroid hormones with glucocorticoid activity increase the uptake of Zn⁺⁺ in HeLa cell cultures. On the basis of the level of Zn⁺⁺ accumulation induced, steroid hormones can be classified into four groups: (a) optimal inducers (e.g., hydrocortisone and prednisolone); (b) suboptimal inducers (e.g., aldosterone and corticosterone); (c) anti-inducers (e.g., progesterone and 17 α-methyl testosterone) which competitively inhibit induction by optimal inducers; and (d) non-inducers (e.g., cortisone and pregnenolone) which neither induce nor inhibit the steroid-mediated increase in Zn⁺⁺ uptake. The ability of an anti-inducer to block the effects of optimal inducers is not the result of inhibition of steroid uptake or an effect on general protein synthesis. Optimal inducers do not increase adenyl cyclase activity of HeLa cells nor can the hormone effects on Zn⁺⁺ uptake be reproduced by 3'-5' cyclic AMP. The prednisolone-induced enhancement of Zn⁺⁺ uptake is gradually lost over two or three days following removal of the hormone. Uptake of Zn⁺⁺ by HeLa cells is not altered by a decrease of sodium concentration in the medium nor by changes in medium osmolarity. The uptake mechanism is not affected by subjecting intact cells to proteolytic enzymes; however, if cells are disrupted the hormone-mediated increase in Zn⁺⁺ accumulation is lost. The Zn⁺⁺ taken up by HeLa cells in the presence or absence of hormone is primarily cytoplasmic in localization and appears to be distributed in a multicompartmental system.     

Anaerobic iron uptake by Escherichia coli.

Assimilation and uptake of iron in anaerobic cultures of Escherichia coli were supported by iron supplied as ferrienterobactin, ferrichrome, and ferrous ascorbate; however, as in the aerobic cultures, ferrichrome A was a poor iron source. Albomycin inhibited both aerobically and anaerobically grown cells. The siderophore outer membrane receptor proteins FepA and FhuA were produced under anaerobic iron-deficient conditions. Anaerobic transport of ferrienterobactin and ferrichrome was inhibited by KCN and dinitrophenol. The Km for ferrienterobactin uptake in anaerobically grown cells was 0.8 microM, and the Vmax was 38 pmol/min per mg, compared with 0.1 microM and 80 pmol/min per mg, respectively, in aerobically grown cells.     

Phenolic and nonphenolic ring deiodinations of iodothyronines in cultured hepatocarcinoma cell hemogenate from monkey

Iodothyronine monodeiodinase activities in homogenates of cultured monkey hepatocarcinoma cells were measured by the deiodination of [3,5-¹²⁵I]triido-l-thyronine or 3-[3′5′-¹²⁵I]triido-l-thyronine (phenolic ring-labeled ‘reverse’ triiodothyronine). The assay system utilized a small ion-exchange column (AG50W-X4, 0.9×～1 cm) to measure ¹²⁵I^?. Both deiodinases were destroyed by boiling for 1 min.Maximal nonphenolic ring deiodination was observed at pH 7.9 whereas maximal phenolic ring deiodination was at pH 6.3. Both reactions were enhanced strongly by dithiothreitol (0.1–5 mM), and slightly by 5 mM β-mercaptoethanol. Phenolic ring deiodination was strongly inhibited by 0.1 mM propylthiouracil. Nonphenolic ring deiodination was accelerated by EDTA (1.2 mM) and inhibited by Mg²⁺ (5 mM). Methylmercaptoimidazol and Mg²⁺, Ca²⁺ and Mn²⁺ (0.1–1.0 mM) had little or no effect on either reaction, but Zn²⁺ (0.1 mM) strongly inhibited both.Both reactions were inhibited by excess iodothyronine analogues at 10 mM to 10μM, and thyroxine was shown to be a competitive inhibitor in both cases. On the basis of relative affinities and inhibitory effects, it appears that the order of affinity for the phenolic ring deiodinase is 3,3′,5′-triiodo-l-thyronine-(rT₃) > l-thyroxine(T₄) > 3,4,3′-triido-l-thyronine(T₃), whereas for the nonphenolic ring deiodinase the order is T₃ > T₄ > rT₃. Diiodotyrosine did not affect their deiodination.     

Uptake and Release of Abscisic Acid by Isolated Photoautotrophic Mesophyll Cells, Depending on pH Gradients

Uptake and release of abscisic acid (AbA) by isolated mesophyll cells of Papaver somniferum is characterized by the following observations: (a) Uptake rate is a linear function of the external AbA concentration in the range from 10⁻⁶ to 5 × 10⁻⁵ molar, and decreases with increasing pH. At any pH, uptake rate is linearly related to the concentration of undissociated abscisic acid, calculated from the pK = 4.7 according to the Henderson-Hasselbalch equation. At low external pH (5.0), AbA accumulation in the cells is about 10-fold. (b) Uptake of AbA is completely inhibited by salts such as KNO₂ or sodium acetate, which decrease the pH gradient between medium and cells. KCN or m-chlorocarbonylcyanide phenylhydrazone inhibits AbA uptake only after longer incubation periods (20-40 minutes). (c) Uptake rate as well as equilibrium concentration is significantly higher in light than in darkness. (d) At low external pH, release of AbA from preloaded cells is strongly stimulated by KNO₂. It is concluded that AbA is distributed between leaf cells and free space according to pH gradients, with the undissociated abscisic acid being the main penetrating species. Uptake and release occur via diffusion, without participation of a carrier.     

Carbohydrate Effects on Amino Acid Transport by Trypanosoma equiperdum*

SYNOPSIS. Uptake of ¹⁴C-labeled alanine, glutamate, lysine, methionine, proline, and phenylalanine by Trypanosoma equiperdum during 2-minute incubations occurred by diffusion and membrane-mediated processes. Amino acid metabolism was not detected by paper chromatography of trypanosome extracts. Most of 18 carbohydrates tested for ability to alter amino acid transport neither changed nor significantly inhibited transport. Glucose, however, stimulated glutamate, lysine and proline transport; fructose stimulated lysine uptake and 2-deoxy-D-glucose increased phenylalanine and methionine absorption. No evidence was found that the carbohydrates acted by binding to amino acid transport “sites.” Glucose inhibition of alanine, phenylalanine, and methionine uptake was linked to glycolysis. The rapid formation of alanine from glucose stimulated alanine release and, when glycolysis was blocked, glucose no longer inhibited alanine transport. Methionine and phenylalanine release was also stimulated by glucose. Glucose changed the ability of lysine, glutamate, and proline to inhibit each others’uptake, indicating that certain amino acids are preferentially absorbed by respiring cells. Analysis of free pool amino acid levels suggested that some amino acid transport systems in T. equiperdum are linked in such a way to glycolysis as to control the cell concentrations of these amino acids.     

Uptake of Benzoic Acid and Chloro-Substituted Benzoic Acids by Alcaligenes denitrificans BRI 3010 and BRI 6011

The mechanism of uptake of benzoic and 2,4-dichlorobenzoic acid (2,4-DCBA) by Alcaligenes denitrificans BRI 3010 and BRI 6011 and Pseudomonas sp. strain B13, three organisms capable of degrading various isomers of chlorinated benzoic acids, was investigated. In all three organisms, uptake of benzoic acid was inducible. For benzoic acid uptake into BRI 3010, monophasic saturation kinetics with apparent K(infm) and V(infmax) values of 1.4 (mu)M and 3.2 nmol/min/mg of cell dry weight, respectively, were obtained. For BRI 6011, biphasic saturation kinetics were observed, suggesting the presence of two uptake systems for benzoic acid with distinct K(infm) (0.72 and 5.3 (mu)M) and V(infmax) (3.3 and 4.6 nmol/min/mg of cell dry weight) values. BRI 3010 and BRI 6011 accumulated benzoic acid against a concentration gradient by a factor of 8 and 10, respectively. A wide range of structural analogs, at 50-fold excess concentrations, inhibited benzoic acid uptake by BRI 3010 and BRI 6011, whereas with B13, only 3-chlorobenzoic acid was an effective inhibitor. For BRI 3010 and BRI 6011, the inhibition by the structural analogs was not of a competitive nature. Uptake of benzoic acid by BRI 3010 and BRI 6011 was inhibited by KCN, by the protonophore 3,5,3(prm1), 4(prm1)-tetrachlorosalicylanilide (TCS), and, for BRI 6011, by anaerobiosis unless nitrate was present, thus indicating that energy was required for the uptake process. Uptake of 2,4-DCBA by BRI 6011 was constitutive and saturation uptake kinetics were not observed. Uptake of 2,4-DCBA by BRI 6011 was inhibited by KCN, TCS, and anaerobiosis even if nitrate was present, but the compound was not accumulated intracellularly against a concentration gradient. Uptake of 2,4-DCBA by BRI 6011 appears to occur by passive diffusion into the cell down its concentration gradient, which is maintained by the intracellular metabolism of the compound. This process could play an important role in the degradation of xenobiotic compounds by microorganisms.     

Hexose transport in normal and SV40-transformed human endothelial cells in culture

The mechanism of glucose entry into human vascular endothelial cells was studied in monolayer cultures of normal (primary) and virally (SV40) transformed umbilical vein endothelium. Radioisotopic uptake studies with the glucose analogues 2-deoxy-D-glucose, and 3-O-methyl-D-glucose, and the nonmetabolizable stereoisomer L-glucose, indicated the presence of a saturable, stereospecific hexose carrier mechanism in both cell types. In other experiments with D-glucose and 3-O-methyl-D-glucose, the phenomenon of countertransport was demonstrable. Hexose transport was not affected by KCN, dinitrophenol, or ouabain, but was inhibited by phloretin and phlorizin in a pattern consistent with facilitated diffusion. Kinetic constants were obtained for both 2-deoxy-D-glucose and 3-O-methyl-D-glucose uptake. Similar Km values (range, 3.3-4.7 mM) were noted with normal and transformed cells, whereas the apparent Vmax was 0.56 nmol/microliter cytosol/minute for primary cells and 1.7-2.5 nmol/mu cytosol/minute for transformed cells. Under standard culture conditions, as well as following 18 hours of serum deprivation, insulin at concentrations up to 10(-5) M did not appear to influence hexose uptake in either cell type. Metabolism of 14C(U)-D-glucose to 14CO2 also was not stimulated by insulin. The presence of an insulin-insensitive, facilitated transport system for glucose in vascular endothelium has relevance for glucose metabolism in this tissue, and potentially for the association of certain vascular diseases (e.g., diabetic microangiopathy, atherosclerosis) with altered glucose homeostasis.     

An inhibitor of arachidonic acid metabolism stimulates luteinizing hormone (LH) release from cultured pituitary cells

5, 8, 11, 14 eicosatetraynoic acid ("ETYA", Roche 3-1428) is a competitive inhibitor of arachidonic acid metabolism. It effectively inhibits the action of both the lipoxygenases and the fatty acid cyclooxygenases both of which utilize arachidonic acid as a substrate. In the present work, we have shown that ETYA stimulates luteinizing hormone (LH) release from cultured pituitary cells (ED50 = 10 micrograms/ml). Stimulation is not due to contaminants present in the preparation, since highly purified ETYA (characterized by GC-MS) stimulates release, while contaminants removed by silicic acid chromatography do not. In addition, neither oxidized solutions of ETYA nor arachidonic acid itself stimulate LH release. ETYA stimulated release is dose dependent and is inhibited by ions which antagonize Ca2+ action. The observation that neither indomethecin (10, 100 micrograms/ml) nor meclofenamate (1.0, 10 micrograms/ml) stimulate LH release suggests that the effect of ETYA cannot be explained by an action on cyclooxygenase. The action of ETYA may be mediated either via an effect on lipoxygenase or through some nonspecific action (such as altered membrane fluidity).     

Sucrose uptake by sugar beet tap root tissue

Sucrose uptake by discs of mature sugar beet root tissue incubated in [¹⁴C]-sucrose exhibited nonsaturating kinetics over the concentration range of 1 to 500 millimolar. Uptake was inhibited by dinitrophenol, sodium cyanide, low O₂, and penetrating sulfhydryl inhibitors. ATPase inhibitors, sodium fluoride, and oligomycin reduced uptake by 20 and 40%, respectively. Uptake as asymmetrically labeled sucrose ([¹⁴C]glucose) occurred with approximately 80% retention of asymmetry, indicating a nonhydrolytic pathway. Uptake was against a concentration gradient and required metabolic energy.     

Iron uptake processes in Mycobacterium vaccae R877R, a mycobacterium lacking mycobactin

The production of exochelins (MV) was established in Mycobacterium vaccae R877R under iron-deficient conditions in concentrations about five times greater than in Mycobacterium smegmatis. M. vaccae does not produce mycobactin nor is salicylic acid secreted into the medium. A simple method is described using 55Fe-labelled culture filtrates for assessing exochelin production and which would be applicable to other mycobacteria. One of the exochelins produced (MV3) is part of an active iron uptake system and another (MV1) is responsible for a passive uptake system. MV3 exochelin has similar chromatographic properties and biological activity to the major exochelin produced by M. smegmatis: iron uptake from MV3 exochelin was inhibited by dinitrophenol, NaN3 and HgCl2, and was judged to be an active transport process. This process was not inhibited by equimolar amounts of ferri-salicylate or ferri-citrate both of which could be used separately as sources of iron for the organism. Uptake from these latter sources was insensitive to metabolic inhibitors and uncouplers. The multiplicity of pathways for iron uptake in a single organism is discussed.     

Energy Transduction by Anaerobic Ferric Iron Respiration in Thiobacillus ferrooxidans

Formate-grown cells of the obligately chemolithoautotrophic acidophile Thiobacillus ferrooxidans were capable of formate- and elemental sulfur-dependent reduction of ferric iron under anaerobic conditions. Under aerobic conditions, both oxygen and ferric iron could be simultaneously used as electron acceptors. To investigate whether anaerobic ferric iron respiration by T. ferrooxidans is an energy-transducing process, uptake of amino acids was studied. Glycine uptake by starved cells did not occur in the absence of an electron donor, neither under aerobic conditions nor under anaerobic conditions. Uptake of glycine could be driven by formate- and ferrous iron-dependent oxygen uptake. Under anaerobic conditions, ferric iron respiration with the electron donors formate and elemental sulfur could energize glycine uptake. Glycine uptake was inhibited by the uncoupler 2,4-dinitrophenol. The results indicate that anaerobic ferric iron respiration can contribute to the energy budget of T. ferrooxidans.     

Involvement of the autonomic nervous system in the in vivo TRH-induced increases in the plasma levels of glucagon, insulin and glucose in rabbits

Thyrotropin-releasing hormone, TRH, increases the plasma levels of glucagon, insulin, glucose and free fatty acids in rabbits. However, TRH has no direct effects on the release of hormones neither from the endocrine pancreas in humans nor from the isolated perfused rat pancreas. The aim of the present study was to investigate if the effects of TRH in rabbits were mediated by the autonomic nervous system. The TRH "Roche"-induced hyperglucagonemia was inhibited by phentolamine (an alpha-receptor blocking drug), yohimbine (an alpha-2 -receptor blocking drug) and atropine. The TRH "Roche"-induced hyperinsulinemia was inhibited by propranolol (a beta-receptor blocking drug). The TRH "Roche"-induced hyperglycemia was inhibited by all four drugs. The TRH "Roche"-induced increases in the plasma levels of free fatty acids were not inhibited by the sympathetic and parasympathetic blocking drugs. The effects of TRH "Roche" on the plasma levels of glucagon, insulin and glucose cannot be explained by increases in the plasma levels of catecholamines. TRH, given intravenously into rabbits, may possibly act on regions in the central nervous system which control carbohydrate metabolism and the release of glucagon and insulin from the endocrine pancreas by sympathetic and parasympathetic mechanisms.     

Uridine uptake by isolated intestinal epithelial cells of guinea pig

Uptake of uridine was studied in isolated intestinal epithelial cells of guinea pig. Uptake was not severely influenced by metabolism. Free uridine was accumulated within cells 13-fold. Uptake was saturable with an apparent Km value of 46 microM and a Vmax of 0.9 nmol/mg protein per min. Uracil inhibited uptake only slightly; adenosine, guanosine and cytosine inhibited strongly. Antimycin A and ouabain inhibited almost 90%. If the extracellular Na+ concentration was decreased to 5 mM, the rate of uptake decreased 6.5-fold. The stimulatory effect of Na+ was related to the transmembraneous Na+-gradient. Cells from jejunum transported about 30% faster than cells from ileum. In conclusion, isolated enterocytes of guinea pig posses an active transport system for uridine.     

D-Gluconate transport in Arthrobacter pyridinolis. Metabolic trapping of a protonated solute.

D-Gluconate uptake was studied in whole cells of Arthrobacter pyridinolis; the uptake activity was inducible, mutable and showed saturation kinetics (Km = 5 micrometer). Uptake of D-gluconate was not mediated by a phosphoenol-pyruvate : hexose phosphotransferase system, nor was it directly energized by ATP. A transmembrane pH gradient, delta pH, of --63 mV was generated by A. pyridinolis cells at pH 6.5, while at pH 7.5, delta pH = 0. Addition of 8 micrometer D-gluconate significantly reduced the delta pH. The transmembrane electrical potential, delta psi, which was --87 mV over a range of pH from 5.5 to 7.5, was unaffected by the presence of substrate. D-Gluconate accumulated at the same rate and as the protonated solute, at both pH 6.5 and 7.5. Experiments in which a diffusion potential was generated in cyanide-treated cells, indicated that the delta psi did not energize transport. Rather, the rate of D-gluconate uptake metabolism: (a) treatment of cells with valinomycin or nigericin, under conditions in which there was a loss of intracellular potassium, inhibited both D-gluconate uptake and the metabolism of pre-accumulated D-gluconate; (b) the effects of cyanide and azide on D-gluconate uptake were much more severe at pH 6.5 than pH 7.5, a pattern which paralleled the effects of these inhibitors on D-gluconate metabolism; (c) extraction and chromatography of intracellular label from D-gluconate uptake revealed that accumulation of unaltered D-gluconate was negligible; (d) a series of mutant strains with lower D-gluconate kinase activities also exhibited low rates of D-gluconate uptake; (e) spontaneous revertants of these mutant strains consistently regained both D-gluconate kinase activity and wild type levels of uptake.     

Lowering of T3 and rise in reverse T3 induced by hyperglucagonemia: altered thyroid hormone metabolism, not altered release of thyroid hormones

Recently we reported that hyperglucagonemia induced by glucagon infusion causes a decline in serum T3 and a rise in reverse T3 in euthyroid healthy volunteers. These changes in T3 and rT3 levels were attributed to altered T4 metabolism in peripheral tissues. However, the contribution of altered release of thyroid hormones by the thyroid gland could not be excluded. Since the release of thyroid hormones is inhibited in primary hypothyroidism and is almost totally suppressed following L-thyroxine replacement therapy, we studied thyroid hormone levels for up to 6 hours after intravenous administration of glucagon in subjects with primary hypothyroidism who were rendered euthyroid by appropriate L-thyroxine replacement therapy for several years. A control study was conducted using normal saline infusion. Plasma glucose rose promptly following glucagon administration demonstrating its physiologic effect. Serum T4, Free T4, and T3 resin uptake were not altered during both studies. Glucagon infusion induced a significant decline in serum T3 (P less than 0.05) and a marked rise in rT3 (P less than 0.05) whereas saline administration caused no alterations in T3 or rT3 levels. Thus the changes in T3 and rT3 were significantly different during glucagon study when compared to saline infusion. (P less than 0.01 for both comparisons). Since, the release of thyroid hormones is suppressed by exogenous LT4 administration in these subjects; we conclude that changes in serum T3 and rT3 observed following glucagon administration reflect altered thyroid hormone metabolism in peripheral tissues and not altered release by the thyroid gland.     

Sugar uptake in soybean (Glycine max) cells in suspension culture

In chlorophylkras soybean ( Glycine max L.) cell suspensioo cultures glucose uptake has been studied using the analogue 3-O-methyIglucose. Uptake could be distinguished into: a) a high affinity phase with K_m= 0.06 m M and b) a low affinity phase with K_m 2.0 m M . The uptake of glucose was accompanied by H⁺-cotransport with a stoichiometry of 0.3 H⁺ per molecule 3-O-methylglucose. Experiments in which sugar uptake was measured in the presence of various inhibitors of respiration and photosynthesis demonstrated that the glucose uptake system was dependent on energy metabolism and the ATP-content of the cells. Efflux experiments in the presence of the uncoupler dinitrophenol confirmed this energy dependency. Glucose uptake did not decrease before the ATP-content of the cells had decreased considerably.     

Exochelin-mediated iron acquisition by the leprosy bacillus, Mycobacterium leprae

Exochelins, water-soluble siderophores of mycobacteria, were isolated and partially purified from culture filtrates of iron-deficiently grown cultures of Mycobacterium neoaurum NCTC 10439 and an armadillo-derived Mycobacterium (ADM 8563). Two biologically active fractions mediating iron uptake were isolated from each bacterium which not only were able to transport iron into the producing organism but also into suspensions of Mycobacterium leprae isolated from armadillo liver. The rate of exochelin-mediated iron uptake into M. leprae was about 1.5% of the rate observed into the producing organisms. The process of iron uptake appears to be by facilitated diffusion as it was not inhibited by HgCl2, NaN3, KCN, dinitrophenol or carbonyl cyanide m-chlorophenylhydrazone. Since no uptake of iron occurred into iron-sufficient ADM cells, this may indicate that M. leprae, as recovered from an animal tissue, had been growing iron-deficiently in order for iron uptake to have been demonstrated in vitro.