Ferritin Overview and Properties

Ferritin

• Ferritin is a blood protein that stores iron.
• A ferritin test measures iron stores in the body.
• Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion.
• This protein is found in almost all living organisms (archaea, bacteria, algae, plants, and animals).
• In humans, ferritin acts as a buffer against iron deficiency and iron overload.
• Ferritin is a globular protein consisting of 24 protein subunits forming a nanocage.
• It facilitates multiple metal-protein interactions, maintaining iron in a soluble, non-toxic form.
• Ferritin without iron is called apoferritin.

Additional Properties of Ferritin

•  Ferritin is approximately 12 nm in diameter
•  The iron core is approximately 8 nm in diameter
•  The protein shell of ferritin is about 12nm in diameter.
•  The composition of the iron core is about 8(FeOOH). FeO. H2PO4

Red-brown color observation

• Ferritin displays a red-brown color
• The molecule structure is aspherical shaped and contains a hollow sphere.

Magnetic Behavior & Protein Composition

• Ferritin protein core has a high-spin state of Fe3+ and exhibits anti-ferromagnetic coupling with S = 5/2
• Protein consists of 24 subunits with a molecular weight of 480 kDa
• 8 hydrophilic channels and 6 hydrophobic channels for controlled access to the core
• The Fe core density is 2.5 times that of apoferritin
• Iron enters via hydrophilic channels and exits via hydrophobic channels
• Average channel diameter measures ~ 0.4 nm (as determined by X-ray)
• Molecules larger than 0.4 nm can still penetrate the interior due to conformational flexibility

Protein Channels

• 4-fold channels lined with leucine residues which are hydrophobic
• 3-fold channels lined with glutamate and aspartate residues which are hydrophilic

Iron Release Mechanism

• Iron is released by dissolving the iron lattice structure
• Dihydroxy fumarate is used as a reducing agent
• Iron reacts with water forming a "water cage" around Fe2+, resulting in a hydrated Fe2+ ion
• Fe2+ is released from ferritin through 3-fold protein channels due to polarity reasons

Transferrin

• A protein that transports iron in blood plasma
• Molecule weight of ~ 80 kDa
• Contains two high-affinity iron (III) binding sites
• This glycoprotein binds iron tightly yet reversibly
• High affinity for Fe(III) (association constant ~10^20 at pH 7.4)
• Produced in the liver

Hemoglobin

• A protein responsible for oxygen transport
• Approximate tetramer of myoglobin
• Molecular weight ~ 64,500 g/mol
• Contains four heme groups bound to four protein chains
• Quaternary globins with four subunits; 2α– chains and 2β– chains
• Peptide chains bound through hydrogen bonds, salt bridges, and hydrophobic interactions

Heme

• Organic planar protoporphyrin consisting of four pyrrole rings, four methyl groups, two vinyl groups, and two propionate side chains.
• Inorganic Fe2+ is bonded to four pyrroles and has additional coordination sites on each side of the heme plane

Hemerythrin

• An oxygen carrier that does not contain heme but contains two iron atoms
• Single chain protein of 115 amino acid residues
• Fe atoms (2Fe2+) bound to 2-carboxylates (Aspartic or Glutamic) with 5-imidazole N from histidines
• In blood in the octomeric form and as monomers, dimers, trimers, or tetramers in tissues

Ferredoxin

• Non-heme Fe-S protein
• Mediates electron transfer in metabolic reactions
• Two types of iron-sulfur clusters: [2Fe-2S] and [4Fe-4S]

Chlorophyll

• Green pigments in thylakoid membranes (found in chloroplasts)
• Involved in photosynthesis
• Two types: Chl-a and Chl-b
• Contain a magnesium (Mg2+) center
• Phytyl group for membrane binding

Cytochromes

• Redox-protein containing heme with a central iron atom
• Involved in electron transport of chains and redox catalysis
• Classified based on heme type and binding mode (a, b, c, d)
• Functional groups affect the cytochrome redox potential

Other Natural Oxygen Carriers

• Respiratory metalloproteins in lower animals (Hemerythrin & Hemocyanins) differ from hemoglobin

This quiz focuses on ferritin, a key blood protein that stores and releases iron in the body. It explores its structure, properties, and biological significance, along with unique observations related to its appearance. Gain a deeper understanding of this essential protein and its role in maintaining iron balance.