Submitochondrial localization of transferrin and iron accumulated by isolated rat liver mitochondria

Konopka, Krystyna; Turska, Ewa

doi:10.1016/0014-5793(79)80892-3

Cited by 10 publications

(8 citation statements)

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“…apotransferrin [28], desferrioxamine [27,30] ferritin [40] or perhaps mitochondria. The latter possibility is supported by the results presented by Konopka and co-workers [24,25], and it is further supported by the results presented in Table 1. When ATP (2.5 mmol/l) is omitted from the incubation medium, the uptake is decreased by about 80 x, but it is not further decreased when succinate is deleted or C I P~Z C ( C N )~ is added.…”

Section: !Iyandcf Qf Surciizute a Tp Und Metabolic Inhibitors On The supporting

confidence: 72%

“…In previous studies [24,25] the iron-uptake experiments were run at 37 'C in Tris buffer. To minimize the temperature-dependent destruction of the mitochondria and the iron-binding properties of the buffer, the present experiments were run at 30°C in Hepes buffer.…”

Section: Resultsmentioning

confidence: 99%

“…(A) Uptake of 59Fe; (B) uptake of "'I has been explained in terms of a closed circuit of endoexocytosis of transferrin with release of iron to the iron-requiring machinery within the cell. In mitochondria iron is accumulated also in excess of transferrin [25]. When during incubation the mitochondria were chased with unlabelled transferrin, ('251)-labelled transferrin remained constant whereas the progressive uptake of 59Fe immediately leveled off (Fig.…”

Section: !Iyandcf Qf Surciizute a Tp Und Metabolic Inhibitors On The mentioning

confidence: 95%

“…It was concluded that transferrin was not a suitable donor of iron to mitochondria. More recently, Konopka [24] and Konopka and Turska [25] reported that rat liver mitochondria accumulated iron from transferrin at a significant rate, about 0.2 nmol/mg protein in 30 min at pH 7.40, in the presence of high concentra-tions of ATP or pyrophosphate. The uptake was linear with time, and about 55'j/, of iron mobilized was recovered in the inner membrane fraction.…”

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Uptake of Iron from Transferrin by Isolated Rat‐Liver Mitochondria Mediated by Phosphate Compounds

Konopka¹,

Romslo

1980

European Journal of Biochemistry

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1. Isolated rat-liver mitochondria accumulate iron from transferrin at neutral pH by a mechanism which is markedly stimulated by small-molecular-weight polyphosphate compounds. The efficiency of the phosphate compounds decreases in the order: pyrophosphate > ATP > GTP > 2,3-bis-(phospho)glycerate > phosphate.2. The uptake has a very low energy dependence, and it does not depend on the hydrolysis of ATP or the saturation of transferrin, but it increases in parallel to the concentration of iron to reach a saturation level of 800-1200 pmol iron/mg protein.3 . Following a chase with unlabelled transferrin, ('251)-labelled transferrin bound to the mitochondria remains constant, whereas the progressive uptake of 59Fe levels off.4. During reincubation of iron-loaded mitochondria up to 30% of the iron is mobilized in the presence of ascorbate and ATP (or apotransferrin).5. The results suggest that iron is mobilized from transferrin by the polyphosphate compounds outside the mitochondria and taken up by the mitochondria in a subsequent reaction.The ferrochelatase reaction represents the ultimate destination for the major part of iron entering the cell. Although it has been claimed that the ferrochelatase resides in part [l] or exclusively in the cytosol [2] most investigators agree that the ferrochelatase is a particulate enzyme confined to the mitochondria [3-51, tentatively on the M-side of the inner membrane [6-81 and depending on unsaturated phospholipids for full activity [9]. Hence, to reach the ferrochelatase iron has to penetrate the mitochondria1 membrane systems.The mechanism(s) by means of which iron is transported across the cytosol, from the plasma membrane to the mitochondria is largely unknown, as is the nature of the cytosol iron-binding ligands. Controversy exists as to whether iron is released from transferrin at the plasma membrane [lo, to operate on the main pathway of iron to the niitochondria in vivo. The uptake of iron by isolated mitochondria has been described, using iron-ATP [18], iron-hydroxyquinoline [19] or iron-sucrose [20] as the iron donor compound. A coherent picture, however, has not emerged.The importance of transferrin as an iron-donor directly to the mitochondria has been emphasized [14,16]. As yet, however, there are only a few studies dealing with the utilization of transferrin iron by isolated mitochondria. Barnes et al. [21] concluded from experiments with sonicated mitochondria that neither transferrin not ferritin functioned as substrate to the ferrochelatase reaction. Ulvik et al. [22] and Koller et al. [23] found that iron was mobilized from transferrin by a mechanism sensitive to uncoupler, high pH and haemin. The release process operated at a rate below that necessary to cope with the ferrochelatase and also at a pH outside that occurring in vivo. It was concluded that transferrin was not a suitable donor of iron to mitochondria. More recently, Konopka [24] and Konopka and Turska [25] reported that rat liver mitochondria accumulated iron from transferrin at a signifi...

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Section: !Iyandcf Qf Surciizute a Tp Und Metabolic Inhibitors On The supporting

confidence: 72%

Section: Resultsmentioning

confidence: 99%

Section: !Iyandcf Qf Surciizute a Tp Und Metabolic Inhibitors On The mentioning

confidence: 95%

mentioning

confidence: 99%

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Uptake of Iron from Transferrin by Isolated Rat‐Liver Mitochondria Mediated by Phosphate Compounds

Konopka¹,

Romslo

1980

European Journal of Biochemistry

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“…It has been speculated that polyphosphates may be responsible for the transfer of iron from transferrin to mitochondria in situ [8,9,13]. From studies on isolated mitochondria it has been shown that transferrin is not a suitable donor of iron to the mitochondria [15,16].…”

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Studies on the Mechanism of Pyrophosphate‐Mediated Uptake of Iron from Transferrin by Isolated Rat‐Liver Mitochondria

Konopka¹,

Romslo

1981

European Journal of Biochemistry

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1. Respiring rat liver mitochondria accumulate iron released from transferrin by pyrophosphate. The amount of iron accumulated is 1-1.5 nmol mg protein-' h-', or approximately 60"/, of the amount of iron mobilized from transferrin.2. The uptake declines if respiration is inhibited, substrate is deleted, or the experiments are run under anaerobic conditions. Substrate depletion and respiratory inhibitors are less inhibitory under anaerobic conditions.3. More than SO"/, of the amount of iron accumulated by aerobic, actively respiring mitochondria can be chelated by bathophenanthroline sulphonate, and with deuteroporphyrin included, up to 30 % of the amount of iron accumulated is recovered as deuteroheme. Iron accumulated by respiration-inhibited mitochondria under aerobic conditions is not available for heme synthesis. 4. With time the uptake of iron increases eightfold relative to the uptake of pyrophosphate. 5.The results are compatible with a model in which ferric iron is mobilized from transferrin by pyrophosphate, ferric iron pyrophosphate is bound to the mitochondria, iron is reduced, dissociates from pyrophosphate and is taken up by the mitochondria. Ferrous iron thus formed is available for heme synthesis.

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Transferrins

Brock¹

1985

Metalloproteins

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Submitochondrial localization of transferrin and iron accumulated by isolated rat liver mitochondria

Cited by 10 publications

References 23 publications

Uptake of Iron from Transferrin by Isolated Rat‐Liver Mitochondria Mediated by Phosphate Compounds

Uptake of Iron from Transferrin by Isolated Rat‐Liver Mitochondria Mediated by Phosphate Compounds

Studies on the Mechanism of Pyrophosphate‐Mediated Uptake of Iron from Transferrin by Isolated Rat‐Liver Mitochondria

Transferrins

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