Cytochrome b5

Cytochrome b5
Cytochrome B5 (rat) bound to itscofactor.Haemin black, iron in orange and iron-bindinghistidineresidues shown as sticks. (PDB:1ICC​)
Identifiers
Symbol	CYB5A
Alt. symbols	CYB5
NCBI gene	1528
HGNC	2570
OMIM	250790
PDB	1JEX
RefSeq	NM_001914
UniProt	P00167
Other data
Locus	Chr. 18q23
Search for Structures Swiss-model Domains InterPro

Cytochrome b5
Identifiers
Symbol	Cyt_B5
Pfam	PF00173
InterPro	IPR001199
PROSITE	PDOC00170
Membranome	211
Available protein structures: Pfam structures/ECOD PDB RCSB PDB;PDBe;PDBj PDBsum structure summary

Cytochromesb₅are ubiquitouselectron transporthemoproteinsfound inanimals,plants,fungiandpurple phototrophic bacteria.Themicrosomalandmitochondrialvariants are membrane-bound, while bacterial and those fromerythrocytesand otheranimal tissuesare water-soluble. The family of cytochromeb₅-like proteins includes (besides cytochromeb₅itself) hemoprotein domains covalently associated with other redox domains in flavocytochrome cytochromeb₂(L-lactate dehydrogenase;EC1.1.2.3), sulfite oxidase (EC1.8.3.1), plant and fungal nitrate reductases (EC1.7.1.1,EC1.7.1.2,EC1.7.1.3), and plant and fungal cytochromeb₅/acyl lipid desaturase fusion proteins.

Structure

3-D structures of a number of cytochromeb₅and yeast flavocytochromeb₂are known. The fold belongs to the α+β class, with two hydrophobic cores on each side of a β-sheet. The larger hydrophobic core constitutes the heme-binding pocket, closed off on each side by a pair of helices connected by a turn. The smaller hydrophobic core may have only a structural role and is formed by spatially close N-terminal and C-terminal segments. The twohistidineresidues provide the fifth and sixth heme ligands, and the propionate edge of the heme group lies at the opening of the heme crevice. Two isomers of cytochromeb₅,referred to as the A (major) and B (minor) forms, differ by a 180° rotation of the heme about an axis defined by the α- and γ-meso carbons.

Cytochromeb₅in some biochemical reactions

EC1.6.2.2cytochrome-b₅reductase

NADH + H⁺+ 2 ferricytochromeb₅→ NAD⁺+ 2 ferrocytochromeb₅

EC1.10.2.1L-ascorbate—cytochrome-b₅reductase

L-ascorbate + ferricytochromeb₅→ monodehydroascorbate + ferrocytochromeb₅

EC1.14.18.2CMP-N-acetylneuraminate monooxygenase

CMP-N-acetylneuraminate + 2 ferrocytochromeb₅+ O₂+ 2 H⁺→ CMP-N-glycoloylneuraminate + 2 ferricytochromeb₅+ H₂O

EC1.14.19.1stearoyl-CoA 9-desaturase

stearoyl-CoA + 2 ferrocytochromeb₅+ O₂+ 2 H⁺→ oleoyl-CoA + 2 ferricytochromeb₅+ H₂O

EC1.14.19.3linoleoyl-CoA 9-desaturase

linoleoyl-CoA + 2 ferrocytochromeb₅+ O₂+ 2 H⁺→ γ-linolenoyl-CoA + 2 ferricytochromeb₅+ H₂O

See also

• Cytochrome b
• Cytochrome b₅deficiency
• P450-containing systems
• Cytochrome b₅,type A

References

• Lederer F (1994). "The cytochrome b5-fold: an adaptable module".Biochimie.76(7): 674–92.doi:10.1016/0300-9084(94)90144-9.PMID7893819.
• Napier JA, Michaelson LV, Sayanova O (February 2003). "The role of cytochrome b5 fusion desaturases in the synthesis of polyunsaturated fatty acids".Prostaglandins, Leukotrienes, and Essential Fatty Acids.68(2): 135–43.doi:10.1016/S0952-3278(02)00263-6.PMID12538077.
• Rivera M, Barillas-Mury C, Christensen KA, Little JW, Wells MA,Walker FA(December 1992). "Gene synthesis, bacterial expression, and 1H NMR spectroscopic studies of the rat outer mitochondrial membrane cytochrome b5".Biochemistry.31(48): 12233–40.doi:10.1021/bi00163a037.PMID1333795.
• Schenkman JB, Jansson I (February 2003). "The many roles of cytochrome b5".Pharmacology & Therapeutics.97(2): 139–52.doi:10.1016/S0163-7258(02)00327-3.PMID12559387.

External links

• PDB:1B5A​ – Solution structure of rat cytochromeb₅(form A)
• PDB:1B5B​ – Solution structure of rat cytochromeb₅(form B)
• PDB:1CXY​ – X-ray structure of cytochromeb₅₅₈fromEctothiorhodospira vacuolata
• Online Mendelian Inheritance in Man(OMIM):250790– Methemoglobinemia due to deficiency of cytochromeb₅