Structure Contains a seven stranded beta sheet Seven alpha helices surround beta sheet

The large hydrophobic beta sheet is solubilzed by the surrounding helices. COIII is thought to be a dimer and holds the Coproporphyrin in the center of two enzymes linked by interacting helicies.

sequence

alignment

Function of Coproporphyrin Oxidase Coproporphyrin Oxidase selectively doubly decarboxilates Coproporphyrin Oxidase III, turning it into Protoporphyrin-IX.

Heme synthesis

Organic Reaction

Transition state of Coproporphyrin The four pyrolles are thought to coordinate to an Aspartate and the two propionate groups to be decarboxylated coordinate to arginine groups.

Active site The active site is thought to be Aspartate 400, Arginine 206, and 401.

Active site Km Kinetic Studies of wild COIII (above) compared to mutagens of Asp 400, Arg 262, and Arg 401 (Right)

Deficiency of Coproporphyrin Oxidase As with all enzymes on the heme and chlorophyll synthetic pathways, a deficiency of COIII causes a build up of precursors as well as a lack porphyrin product. The build up leads to surface lesions, and sensitivity to light in plants and animals. Leafs with various mutagens in COIII

references Lash, T.D. The enigma of coprpporphyrinogen oxidase: How does this unusual enzyme carry out oxidative decarboxylations to afford vinyl groups? Bio. & Med. Chem. Lett. 2005, Stephenson, J.R.; Stacey J.A.; Morgenthaler, J. B; Friesen, J.A.; Lash, T.D.; Jones, M.A. Role of aspartate 400, arginine 262, and arginine 401 in the catalytic mechanism of human coproporphyrinogen oxidase Protein Science 2007, Ishikawa, A.; Okamato, H.; Iwasaki, Y.; Asahi, T.; A deficiency of coproporphyrinogen III oxidase causes lesion formation in Arabidopsis, The Plant Journal 2001, Nelson, D. L., & Cox, M. M. (2005). Lehninger Principles of Biochemistry. New York: W.H. Freeman and Company.

Coproporphyrin Oxidase: For America