MetaCyc Enzyme: heme oxygenase 1

Gene: pbsA1 Accession Number: G-10574 (MetaCyc)

Synonyms: HO1, sll1184

Species: Synechocystis sp. PCC 6803

In animals, heme oxygenase is a part of a degradative pathway, catalyzing the rate limiting step of opening the tetrapyrrole macrocycle of protoheme, in the degradation of heme to bilirubin, a process that ensures iron recycling. The enzyme, which uses heme as both a substrate and a cofactor, produces biliverdin, iron, and carbon monoxide.

In cyanobacteria, the enzyme is involved in a biosynthetic pathway. The phytobilin chromophores of phycobiliproteins and phytochromes are biosynthesized from heme in a pathway that begins with the conversion of protoheme to biliverdin IXa.

The enzyme from Synechocystis sp. PCC 6803 is encoded by the pbsA1 gene, and was identified by its similarity to animal macrosomal heme oxidases [Cornejo98]. The gene was cloned and expressed in Escherichia coli. The coli cells expressing the gene became green colored due to the accumulation of biliverdin IXa. Activity was verified in cell extracts using mesoheme as the substrate and reduced ferredoxin [Cornejo98]. When the gene was transformed to an Synechocystis sp. PCC 6803 mutant deficient in phytochrome responses (HY1), the phenotype was restored to normal [Willows00].

A crystal structure of the enzyme in complex with heme has been obtained at a resolution of 2.5 A [Sugishima04]. A docking model of the enzyme and ferredoxin suggests indirect electron transfer from an iron-sulfur cluster in ferredoxin to the heme iron of heme-HO1.

Molecular Weight of Polypeptide: 27.051 kD (from nucleotide sequence), 30.0 kD (experimental) [Cornejo98 ]

Unification Links: Entrez-gene:953483 , Protein Model Portal:P72849 , SMR:P72849 , String:1148.sll1184 , UniProt:P72849

Relationship Links: InterPro:IN-FAMILY:IPR002051 , InterPro:IN-FAMILY:IPR016053 , InterPro:IN-FAMILY:IPR016084 , InterPro:IN-FAMILY:IPR018207 , Panther:IN-FAMILY:PTHR10720 , PDB:Structure:1WE1 , Pfam:IN-FAMILY:PF01126 , Prints:IN-FAMILY:PR00088 , Prosite:IN-FAMILY:PS00593

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Created 27-Mar-2008 by Caspi R , SRI International

Enzymatic reaction of: heme oxygenase

EC Number:

ferroheme b + 3 an reduced unknown electron acceptor + 3 oxygen + 2 H+ <=> biliverdin-IX-α + Fe2+ + carbon monoxide + 3 an oxidized unknown electron acceptor + 3 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phycocyanobilin biosynthesis


Cornejo98: Cornejo J, Willows RD, Beale SI (1998). "Phytobilin biosynthesis: cloning and expression of a gene encoding soluble ferredoxin-dependent heme oxygenase from Synechocystis sp. PCC 6803." Plant J 15(1);99-107. PMID: 9744099

Sugishima04: Sugishima M, Migita CT, Zhang X, Yoshida T, Fukuyama K (2004). "Crystal structure of heme oxygenase-1 from cyanobacterium Synechocystis sp. PCC 6803 in complex with heme." Eur J Biochem 271(22);4517-25. PMID: 15560792

Willows00: Willows RD, Mayer SM, Foulk MS, DeLong A, Hanson K, Chory J, Beale SI (2000). "Phytobilin biosynthesis: the Synechocystis sp. PCC 6803 heme oxygenase-encoding ho1 gene complements a phytochrome-deficient Arabidopsis thalianna hy1 mutant." Plant Mol Biol 43(1);113-20. PMID: 10949378

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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