Heme C

Heme C is a type of heme, which is a porphyrin ring complexed with an iron atom. It's a prosthetic group found in certain proteins, most notably cytochromes involved in electron transport chains. Unlike heme B, the most common heme, heme C is covalently linked to the apoprotein (the protein portion of the enzyme) through thioether bonds formed between cysteine residues and the vinyl groups on the porphyrin ring. These covalent linkages make heme C a permanently bound prosthetic group within the protein structure.

The iron atom in heme C can exist in either the ferrous (Fe²⁺) or ferric (Fe³⁺) oxidation state. This ability to cycle between these two oxidation states allows heme C to function as an electron carrier in redox reactions.

Heme C is critical for the function of many enzymes involved in cellular respiration and photosynthesis. It plays a central role in mitochondrial electron transport and bacterial respiratory chains. Examples of proteins containing heme C include cytochrome c and cytochrome c oxidase.

The specific properties of heme C, such as its redox potential, are influenced by its surrounding protein environment. The protein structure dictates the access of substrates and the stability of the different oxidation states of the iron atom, thus fine-tuning the function of the heme C-containing enzyme.