Heme c

Heme c

Heme c is a type of heme, which is an essential prosthetic group found in various hemoproteins. It plays a crucial role in electron transfer and redox reactions in biological systems. Heme c is distinct from other heme types, such as Heme a and Heme b, due to its unique covalent attachment to the protein via thioether bonds.

Structure

Heme c consists of an iron ion (Fe) coordinated within a porphyrin ring, specifically a protoporphyrin IX. The distinguishing feature of heme c is the covalent attachment of the porphyrin ring to the protein via two thioether bonds formed between the vinyl groups of the porphyrin and cysteine residues of the protein. This covalent linkage is a defining characteristic that differentiates heme c from other heme types.

Function

Heme c is primarily involved in electron transfer processes. It is a key component of cytochrome c, a small heme protein associated with the inner membrane of the mitochondria. Cytochrome c plays a vital role in the electron transport chain, facilitating the transfer of electrons between Complex III (cytochrome bc1 complex) and Complex IV (cytochrome c oxidase) in the process of oxidative phosphorylation.

Biological Importance

The presence of heme c in cytochrome c is critical for cellular respiration and energy production. The electron transfer facilitated by cytochrome c is essential for the generation of ATP, the energy currency of the cell. Additionally, cytochrome c is involved in the intrinsic pathway of apoptosis, where it acts as a signaling molecule to trigger programmed cell death.

Synthesis

The synthesis of heme c involves the incorporation of iron into protoporphyrin IX, followed by the covalent attachment of the porphyrin to the protein. This process occurs in the mitochondria and requires specific enzymes, such as cytochrome c heme lyase, which catalyzes the attachment of heme c to apocytochrome c.

Clinical Significance

Alterations in heme c-containing proteins, such as cytochrome c, can have significant clinical implications. Mutations affecting cytochrome c can lead to disorders in energy metabolism and have been implicated in various diseases, including neurodegenerative disorders and cancer.

Also see

• Heme a
• Heme b
• Cytochrome c
• Electron transport chain
• Oxidative phosphorylation