IUBMB Enzyme Nomenclature


Accepted name: heme oxygenase (mycobilin-producing)

Reaction: (1) protoheme + 3 reduced acceptor + 3 O2 = mycobilin a + Fe2+ + 3 acceptor + 3 H2O
(2) protoheme + 3 reduced acceptor + 3 O2 = mycobilin b + Fe2+ + 3 acceptor + 3 H2O

For diagram of reaction click here.

Glossary: mycobilin a = 8,12-bis(2-carboxyethyl)-19-formyl-3,7,13,18-tetramethyl-3,17-divinylbiladiene-ab-1,15(21H)-dione
mycobilin b = 8,12-bis(2-carboxyethyl)-19-formyl-2,7,13,17-tetramethyl-3,18-divinylbiladiene-ab-1,15(21H)-dione

Other name(s): mhuD (gene name)

Systematic name: protoheme,donor:oxygen oxidoreductase (mycobilin-producing)

Comments: The enzyme, characterized from the bacterium Mycobacterium tuberculosis, is involved in heme degradation and iron utilization. The enzyme binds two stacked protoheme molecules per monomer. Unlike the canonical heme oxygenases, the enzyme does not release carbon monoxide or formaldehyde. Instead, it forms unique products, named mycobilins, that retain the α-meso-carbon at the ring cleavage site as an aldehyde group. EC, NADPH-hemoprotein reductase, can act as electron donor in vitro.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number:


1. Chim, N., Iniguez, A., Nguyen, T.Q. and Goulding, C.W. Unusual diheme conformation of the heme-degrading protein from Mycobacterium tuberculosis. J. Mol. Biol. 395 (2010) 595-608. [PMID: 19917297]

2. Nambu, S., Matsui, T., Goulding, C.W., Takahashi, S. and Ikeda-Saito, M. A new way to degrade heme: the Mycobacterium tuberculosis enzyme MhuD catalyzes heme degradation without generating CO. J. Biol. Chem. 288 (2013) 10101-10109. [PMID: 23420845]

3. Graves, A.B., Morse, R.P., Chao, A., Iniguez, A., Goulding, C.W. and Liptak, M.D. Crystallographic and spectroscopic insights into heme degradation by Mycobacterium tuberculosis MhuD. Inorg. Chem. 53 (2014) 5931-5940. [PMID: 24901029]

[EC created 2017]

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