This document summarizes metal ion transport and storage in biological systems. It discusses the general properties of transport systems like ionophores, ion channels, and ion pumps. Specific mechanisms for transporting ions like sodium, potassium, iron, and calcium are described. Metal storage is achieved through proteins like ferritin and metallothionein. Problems associated with transporting and storing metal ions across membranes are also highlighted.

1. Metal Ion Transport and Storage
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2. Bio Inorganic Chemistry
Presentation 01
Group Members.
• H.T.P. Dayananda.
• A.K.A. Perera.
• H.S. Alwis.
• S.L. Weerasinghe.
• K.G. Sapumohotti
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3. OUTLINE
• Metal Ions Bioavailability.
• General Properties of Transport Systems.
• Mechanisms of metal ion storage & resistance.
• Specific Metal Ions
– K / Na
– Fe
– Ca
• Problems of Metal Ion Transport.
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4. Introduction
• Chemical Properties.
– Catalyze oxidation & reduction. eg:Cu
– Act as Lewis acid in hydrolytic enzymes. eg: Zn
– Structural Co-factor.
• Problems.
– Genetic diseases.
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5. Metal Ion Bioavailability.
• Bioavailability term implies more than just the
incidence of an element on Earth and includes its
prevalence in environment where life is found.
– Nickel in the Earth's core.
– Zinc sulfide in the biosphere.
– Molybdenum in the ocean
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6. Bioavailability.
• Fe is fourth most abundent element in Earth’s
crust.
• For mammalian cells,the source of metal ions
is the blood plasma.
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7. General properties of transport
systems.
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8. Ionophores
special carrier molecules that wrap around
metal ions.
Pass through the membrane by diffusion.
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9. Ion Channels
Large pores in membrane.
Allow to movement of substrate across by
diffusion.
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10. Ion Channels.
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11. Ion pumps
Molecules using energy to transport ions in
one direction through a membrane.
Primary active transport system.
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12. Carriers
Bind to substrate on one side of membrane.
Confrmatinal change.
Release the substrate on opposite side of
membrane.
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13. Carriers
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14. Mechanisms for membrane Transport.
• Passive Transport :
Movement of ions.
Due to concentration gradient.
Requiring no energy source.
Ionophores , Ion channels.
• Active Transport :
Movement of ions.
Against the concentration gradient.
Requiring energy from ATP hydrolysis.
Ion pumps.
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15. Metal ion storage & Resistance
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16. Mechanisms of metal ion storage &
resistance
• Organisms store metal ions.
• It have more benefits.
• Allow the accumulation of high intacellular lebels of
metal ions without the toxic.
• Understood mechanis of metal ion storage
are,
Ferritin
Metallothionein
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17. Ferritin
• Ferritin are disscussed in greater detail under
Iron Storage.
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18. Metallothionein
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19. Metallothionein
• cytopalmic metal- binding protein.
• Involved in ion storage & detoxification.
• Small ,cysteine-rich proteins that bind
Zn2+,Cd2+ Cu2+ & cys ligands.
• Found in cyanobacteria,fungi,plants ,insects &
vertebrates.
• Bind metal ions with high affinity.
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20. Sodium -Na+
• Major cation in human body
• Important for
– membrane function
– Nerve impulses
– Muscle contraction
– Prevent blood clotting
• Present in stomach walls, gallbladder and

21. Potassium- K+
• Important for
– Membrane function
– Maintaining osmotic balance
– Cofactor in photosynthesis and respiration

22. Sodium &Potassium
• Concentration of [Na+]
&[K+]
– Inside red blood cells [Na+]
=0.01M [K+] =0.09M
– Outside red blood cells
[Na+] =0.16M [K+] =0.01M
• Ion pump is required
to maintain concentration
gradient
• Also
– Ionphore
– Ion channel are used for
Na & K ion transport

23. Na -K Pump

24. Mechanism of Na+ –K+ pump

25. Sodium –Potassium Pump
• Na+ /K+ - ATPase
-ATP + 3Na+
– Phosphorylation of enzyme
– Eversion & releasing Na+
– Binding of 2K+
– Dephosphorylation
– Eversion & releasing K+
• 3Na+ + 2K+ +ATP4- +H2O
3Na+ + 2K+ +ATP3- +H3PO 43- +
H+

26. Selectivity of the process
• Depends upon
– Differences in ionic radii.
– Coulomb forces
• Bases stronger than H2O – bind preferentially
to the hard acid Na
• Bases weaker than H2O – bind preferentially to
the hard acid K

27. Iron
• Most abundant transition element.
• Involve in many biological roles.
e.g. oxygen transport.
electron transport.
metabolism.
• Versatility :
Fe2+ / Fe3+
High spin / low spin
Hard / soft
Labile / inert
Co-ordination number 4 , 5, 6
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28. Transport of iron
• Organisms mobilize Fe.
• Three general ways which mobilization is
accomplished.
Chelation.
Reduction.
Acidification.
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29. chelation
Bacteria, fungi, and some plants use chelating
agents called “siderophores” to obtain ions.
Siderophores :
Small molecules released into the environment.
Complexation of fe3+ solubilizes its for uptake.
Ligands are catechol and hydroxamic acid
chelates.
Mainly 3 examples.
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30. Siderophores
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31. Iron
• Enterobactin :
3 catechol chelates bound to a 1 membered ring.
Complex anion is soluble.
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32. iron
• ferrichromes :
• 3 hydroxamic acids, cyclic peptide.
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33. iron
• Ferrioxamines :
• 3 hydroxamic acids , acyclic peptide.
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34. Reduction
• Reduce extracellular fe3+ to fe2+
• Reduction increase solubility & support the
transportation of particular Fe.
• Reduction of Fe3+ mediated by
“ferrireductases”
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35. Acidification.
• Conjuction with reduction dependent
pathways.
• Acidify extracellular environment.
• Increase the soluble ferric concentation by
inbiting formation of hydrolysis prducts
[Fe(OH)3]
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36. Mammalian iron transport.
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37. Mammalian iron transport
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38. Receptor mediated endocytsis
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39. Transferrin
• 700 amino acid serum protein which has
higher affinity towards ferric ions.
Synthesized in liver.
Secreted into the plasma.
From a chelate complex.
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40. Transferrin
• Transferrin : mammelian transport αβ dimer
protein.
– Ironcaptured as Fe2+ & oxidized to Fe3+
– Co32- ust bind at same time ; Synergism.
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41. Transferrin
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42. Mammalian Iron Storage
• Ferritin
Found in vertebrates , plants , fungi & bacteria.
Primary site of Fe storage.
It has outer coat of protein an inner core of
hydrous ferric oxide.
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43. Ferritin
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44. Ferritin
• The iron strorage protein.
– Ferritin is a protein, store iron & release it in a
controlled fashion.
– If the blood has too little iron, ferritin can release
more.
– If the blood or tissues of body have too much iron,
ferritin can help to store the excess iron.
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45. Ferritin
• Ferritin is synthesized as needed.
– Normal iron load is 3 – 5 grams in human.
– Ferritin is stored in cell in the bone marrow,liver &
spleen.
– Siderosis : iron overload
» Deposits in liver, kidneys & heart
» Treated by chelation therapy. (desferrioxamine)
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46. Calcium
• Present in bones, enamel, shells
• Important for
– Signal pathways
– Skeletal material
– Maintaining potential difference across
membranes
• Concentration
– Outside cell = 0.001M
– Inside cell = 10-7 M

47. Calcium Regulaton.
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48. Calcium storage
• Egg shells. Coral skeleton –CaCO3
• Bones & teeth – Calcium Hydroxyapatite in
collagen
– Collagen – triple helix fibrous protein
– Hydroxyapatite-around collagen
If required Ca2+ can be released and reabsorbed.

49. Calcium pump
• Ca is in cytoplasm.
• pumped in to sarcoplasmic reticulum (A form of
endoplasmic reticulum)
• Up to 0.03M
• Inside SR Ca is bound by calsequestrin
• Hormone induced ion channels releases Ca from
SR to muscle cell
• Muscle contraction is triggered by sudden
release of Ca

50. Calcium pump
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51. Transport & storage problems.
• Capture of trace ions from the environment
– Control the concentration.
– Bulk ones present in high concentration.
– Trace ones actively accumulated &insoluble.
• Selectivity of ion uptake is essential.
– Toxic ions excluded.
– Beneficial ions accumulated.
– Specialized molecules have evolved.
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52. Transport & storage problems.
• Charged ions pass through a Hydrophobic
Membrane.
• Neutral gases & low charge density ions move directly
but high charge density require help.
• Metal ions transport to their location for use
& storage.
• Release from ligand & storage require additional
molecules.
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