Cytochrome b5 reductases

Cytochrome b5 reductases
	Ribbon model of the soluble isoform of B5R3 (methaemoglobin reductase), with FAD as domes, according to PDB 1UMK
Mass / length primary structure	differently
Cofactor	FAD
Identifier
Gene name (s)	CYB5R1 , CYB5R2 , CYB5R3 , CYB5R4 , CYB5RL
Enzyme classification
EC, category	1.6.2.2 , oxidoreductase
Response type	Redox reaction
Substrate	NADH + Fe 3+ cytochrome b5
Products	NAD + + H + + Fe 2+ cytochrome b5
Occurrence
Parent taxon	Mammals

Cytochrome b ₅ reductases (CBR, B5R) , more specifically NADH-cytochrome b ₅ reductase, formerly methemoglobin reductase, are enzymes in mammals , the reduction of to the protein cytochrome b ₅ bound heme with the complexed iron - Ion from trivalent catalyze into the divalent state . At the same time, NADH is oxidized to NAD ⁺ and H ⁺ by withdrawing 2 electrons . This redox reaction is essential for the reduction of methemoglobin , the recycling of ascorbate , in lipid metabolism , and in general for the transfer of electrons from NADH to other substrates. Mutations in CYB5R3 - gene are responsible for hereditary methemoglobinemia responsible.

The B5R enzymes are structurally and functionally related to the NAD (P) H: nitrate reductases in plants and fungi. Both families belong to the superfamily of flavoprotein pyridine nucleotide cytochrome reductases , which are found in eukaryotes and bacteria .

In humans there are five paralogous cytochrome b ₅ reductase genes , each of which can form several different enzymes through alternative splicing :

Gene name	protein	OMIM	variants	size	comment
CYB5R1	Q9UHQ9	608341	1	305	single pass membrane protein ( nucleolus ); widely expressed
CYB5R2	Q6BCY4	608342	2	276	not expressed everywhere; responsible for lucigenin chemiluminescence
CYB5R3	P00387	250800	M / S	300/ 275	Membrane protein (M, endoplasmic reticulum and mitochondrion ) and soluble isoform (S, methemoglobin reductase ); S only expressed in erythrocytes , responsible for type I methaemoglobinemia .
CYB5R4	Q7L1T6	608343	1	521	soluble; endoplasmic reticulum; widely expressed; protects the pancreas from oxidative stress
CYB5RL	Q6IPT4		3	314/ 167/ 247

Individual evidence