Target type: molecularfunction
Catalysis of the reaction: NAD(P)H + H+ + 2 ferricytochrome b(5) = NAD(P)+ + 2 ferrocytochrome b(5). [EC:1.6.2.2, ISBN:0198547684]
Cytochrome-b5 reductase activity, acting on NAD(P)H, is a crucial enzymatic function involved in the reduction of cytochrome b5, a heme-containing protein essential for various cellular processes. This activity is catalyzed by a family of enzymes known as cytochrome-b5 reductases, which utilize NADH or NADPH as electron donors. The core function of these enzymes involves transferring electrons from NAD(P)H to cytochrome b5, thereby reducing the latter. This reduction is essential for cytochrome b5's role in several critical cellular processes, including:
- **Fatty acid desaturation:** Cytochrome b5, in its reduced form, acts as a cofactor for fatty acyl desaturases, enzymes responsible for introducing double bonds into fatty acid chains. This process is crucial for the synthesis of unsaturated fatty acids, essential components of cell membranes and signaling molecules.
- **Steroid biosynthesis:** Cytochrome b5 reductase activity is also involved in the biosynthesis of steroid hormones. In this process, cytochrome b5, reduced by the reductase, participates in electron transfer reactions required for the conversion of cholesterol into various steroid hormones.
- **Drug metabolism:** Cytochrome b5 reductase is implicated in the metabolism of certain drugs, particularly those involving the cytochrome P450 system. This system utilizes cytochrome b5 as an electron carrier in drug detoxification and metabolism.
- **Redox homeostasis:** Cytochrome b5 reductase contributes to maintaining redox homeostasis by regulating the balance between oxidized and reduced forms of cellular components, including cytochrome b5 itself.
In essence, cytochrome-b5 reductase activity, acting on NAD(P)H, plays a pivotal role in diverse cellular functions by facilitating the reduction of cytochrome b5. This reduction is essential for cytochrome b5's involvement in fatty acid desaturation, steroid biosynthesis, drug metabolism, and redox homeostasis. The specific mechanisms and implications of this activity vary depending on the cellular context and the specific cytochrome b5 reductase involved.'
"
| Protein | Definition | Taxonomy |
|---|---|---|
| NAD | An NAD(P)H dehydrogenase [quinone] 1 that is encoded in the genome of human. [PRO:DNx, UniProtKB:P15559] | Homo sapiens (human) |
| NADH-cytochrome b5 reductase 3 | An NADH-cytochrome b5 reductase 3 that is encoded in the genome of human. [PRO:DNx, UniProtKB:P00387] | Homo sapiens (human) |
| Compound | Definition | Classes | Roles |
|---|---|---|---|
| 4'-bromoflavone | 4'-bromoflavone: structure in first source | ||
| beta-naphthoflavone | beta-naphthoflavone : An extended flavonoid resulting from the formal fusion of a benzene ring with the f side of flavone. beta-Naphthoflavone: A polyaromatic hydrocarbon inducer of P4501A1 and P4501A2 cytochromes. (Proc Soc Exp Biol Med 1994 Dec:207(3):302-308) | extended flavonoid; naphtho-gamma-pyrone; organic heterotricyclic compound | aryl hydrocarbon receptor agonist |
| beta-lapachone | beta-lapachone : A benzochromenone that is 3,4-dihydro-2H-benzo[h]chromene-5,6-dione substituted by geminal methyl groups at position 2. Isolated from Tabebuia avellanedae, it exhibits antineoplastic and anti-inflammatory activities. beta-lapachone: antineoplastic inhibitor of reverse transcriptase, DNA topoisomerase, and DNA polymerase | benzochromenone; orthoquinones | anti-inflammatory agent; antineoplastic agent; plant metabolite |
| vitamin k 3 | Vitamin K 3: A synthetic naphthoquinone without the isoprenoid side chain and biological activity, but can be converted to active vitamin K2, menaquinone, after alkylation in vivo. | 1,4-naphthoquinones; vitamin K | angiogenesis inhibitor; antineoplastic agent; EC 3.4.22.69 (SARS coronavirus main proteinase) inhibitor; human urinary metabolite; nutraceutical |
| sulforaphane | sulforaphane : An isothiocyanate having a 4-(methylsulfinyl)butyl group attached to the nitrogen. sulforaphane: from Cardaria draba L. | isothiocyanate; sulfoxide | antineoplastic agent; antioxidant; EC 3.5.1.98 (histone deacetylase) inhibitor; plant metabolite |
| c 1303 | C 1303: DNa-binding drug; structure given indicates that the cpd should be the dimethylamino cpd, but it is named as the diethylamino cpd | ||
| nsc 366140 | NSC 366140: a 9-methoxypyrazoloacridine; structure given in first source | ||
| propylthiouracil | 6-propyl-2-thiouracil : A pyrimidinethione consisting of uracil in which the 2-oxo group is substituted by a thio group and the hydrogen at position 6 is substituted by a propyl group. Propylthiouracil: A thiourea antithyroid agent. Propythiouracil inhibits the synthesis of thyroxine and inhibits the peripheral conversion of throxine to tri-iodothyronine. It is used in the treatment of hyperthyroidism. (From Martindale, The Extra Pharmacopeoia, 30th ed, p534) | pyrimidinethione | antidote to paracetamol poisoning; antimetabolite; antioxidant; antithyroid drug; carcinogenic agent; EC 1.14.13.39 (nitric oxide synthase) inhibitor; hormone antagonist |
| 5-methoxy-1,2-dimethyl-3-((4-nitrophenoxy)methyl)indole-4,7-dione | 5-methoxy-1,2-dimethyl-3-((4-nitrophenoxy)methyl)indole-4,7-dione: structure in first source | ||
| bisantrene | |||
| 4,3',5'-tri-o-methylpiceatannol | |||
| ly 341495 | xanthenes | ||
| memoquin | memoquin: structure in first source | ||
| dicumarol | Dicumarol: An oral anticoagulant that interferes with the metabolism of vitamin K. It is also used in biochemical experiments as an inhibitor of reductases. | hydroxycoumarin | anticoagulant; EC 1.6.5.2 [NAD(P)H dehydrogenase (quinone)] inhibitor; Hsp90 inhibitor; vitamin K antagonist |
| ethyl biscoumacetate | Ethyl Biscoumacetate: A coumarin that is used as an anticoagulant. It has actions similar to those of WARFARIN. (From Martindale, The Extra Pharmacopoeia, 30th ed, p226) | hydroxycoumarin | |
| nsc 158393 | NSC 158393: structure given in first source |