IUBMB Enzyme Nomenclature


Accepted name: heme oxygenase (biliverdin-producing, ferredoxin)

Reaction: protoheme + 6 reduced ferredoxin [iron-sulfur] cluster + 3 O2 + 6 H+ = biliverdin + Fe2+ + CO + 6 oxidized ferredoxin [iron-sulfur] cluster + 3 H2O

For diagram of reaction click here.

Other name(s): HO1 (gene name); HY1 (gene name); HO3 (gene name); HO4 (gene name); pbsA1 (gene name)

Systematic name: protoheme,reduced ferredoxin:oxygen oxidoreductase (α-methene-oxidizing, hydroxylating)

Comments: The enzyme, found in plants, algae, and cyanobacteria, participates in the biosynthesis of phytochromobilin and phytobilins. The terminal oxygen atoms that are incorporated into the carbonyl groups of pyrrole rings A and B of biliverdin are derived from two separate oxygen molecules. The third oxygen molecule provides the oxygen atom that converts the α-carbon to CO. Unlike this enzyme, which uses ferredoxin as its electron donor, the electron source for the related mammalian enzyme (EC is EC, NADPH—hemoprotein reductase.

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


1. Montgomery, B.L. and Lagarias, J.C. Phytochrome ancestry: sensors of bilins and light. Trends Plant Sci 7 (2002) 357-366. [PMID: 12167331]

2. Sugishima, M., Migita, C.T., Zhang, X., Yoshida, T. and Fukuyama, K. Crystal structure of heme oxygenase-1 from cyanobacterium Synechocystis sp. PCC 6803 in complex with heme. Eur. J. Biochem. 271 (2004) 4517-4525. [PMID: 15560792]

3. Dammeyer, T. and Frankenberg-Dinkel, N. Function and distribution of bilin biosynthesis enzymes in photosynthetic organisms. Photochem Photobiol Sci 7 (2008) 1121-1130. [PMID: 18846276]

[EC created 2016]

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