Coproporphyrinogen III oxidase

Structure of coproporphyrinogen III oxidase

Coproporphyrinogen III oxidase is an enzyme that plays a crucial role in the heme biosynthesis pathway. It catalyzes the oxidative decarboxylation of coproporphyrinogen III to form protoporphyrinogen IX, a key step in the production of heme.

Function

Coproporphyrinogen III oxidase is responsible for converting coproporphyrinogen III into protoporphyrinogen IX by removing two carboxyl groups from the propionate side chains of rings A and B of the porphyrin ring. This reaction is essential for the subsequent steps in the heme biosynthesis pathway, which ultimately lead to the formation of heme, an important component of hemoglobin, myoglobin, and various cytochromes.

Structure

The enzyme is typically a homodimer, with each subunit containing a flavin adenine dinucleotide (FAD) cofactor that is essential for its catalytic activity. The structure of coproporphyrinogen III oxidase has been elucidated through X-ray crystallography, revealing details about its active site and the binding of its substrate.

Mechanism

The enzymatic mechanism involves the oxidation of the methylene bridges of coproporphyrinogen III, facilitated by the FAD cofactor. This process results in the release of two molecules of carbon dioxide and the formation of protoporphyrinogen IX. The reaction is oxygen-dependent and occurs in the mitochondria of eukaryotic cells.

Clinical significance

Deficiencies in coproporphyrinogen III oxidase activity can lead to disorders such as hereditary coproporphyria, a type of porphyria characterized by the accumulation of porphyrin precursors. Symptoms of hereditary coproporphyria can include abdominal pain, neurological disturbances, and photosensitivity.

Heme biosynthesis pathway

Heme biosynthesis pathway

Coproporphyrinogen III oxidase is part of the heme biosynthesis pathway, which involves multiple enzymatic steps starting from glycine and succinyl-CoA. The pathway includes the following steps:

1. Formation of δ-aminolevulinic acid (ALA) 2. Conversion of ALA to porphobilinogen 3. Formation of hydroxymethylbilane 4. Cyclization to form uroporphyrinogen III 5. Decarboxylation to form coproporphyrinogen III 6. Oxidation by coproporphyrinogen III oxidase to form protoporphyrinogen IX 7. Oxidation to form protoporphyrin IX 8. Insertion of iron to form heme

Related pages

• Heme
• Porphyria
• Hemoglobin
• Cytochrome