Cytochrome

Cytochrome c oxidase subunit VB (COX5B) is the terminal enzyme of the mitochondrial respiratory chain. COX5B is a multi-subunit enzyme complex which couples the transfer of electrons from cytochrome c to molecular oxygen and contributes to a proton electrochemical gradient across the inner mitochondrial membrane. There are two isoforms of COX5:COX5a and COX5b. Transcription of COX5A (the aerobic isoform) is up-regulated as the rate of cellular respiration increases, when oxygen levels within the cell are high. However, when oxygen levels are low, COX5B (the hypoxic isoform) transcription increases and functions to maximize the turnover rate of the COX apoenzyme.

P450 Oxidoreductase, also known as POR is a flavoprotein which contributes electrons to all microsomal P450 enzymes. POR is localized to the endoplasmic reticulum, where it is also capable of transfering electrons to heme oxygenase as well as cytochrome b5. POR is structurally related to two separate flavoprotein families; first one is ferredoxin nucleotide reductase and the second flavodoxin.

P450 Oxidoreductase, also known as POR is a flavoprotein which contributes electrons to all microsomal P450 enzymes. POR is localized to the endoplasmic reticulum, where it is also capable of transfering electrons to heme oxygenase as well as cytochrome b5. POR is structurally related to two separate flavoprotein families; first one is ferredoxin nucleotide reductase and the second flavodoxin.

SCO2 protein is a member of the SCO1/2 family. SCO1 and SCO2 proteins are found on the inner membrane of the mitochondria and takes a vital part copper insertion or transport to the active site of cytochrome c oxidase (COX). Flaws in SCO2 are the reason for deadly infantile cardioencephalomyopathy with cytochrome c oxidase deficiency (FIC) which is characterized by hypertrophic cardiomyopathy, lactic acidosis, and gliosis. Heart and skeletal muscle display declines in cytochrome c oxidase (COX) activity, while liver and fibroblasts show mild COX deficiencies.

CYP2E1, also known as Cytochrome P450 2E1 belongs to the cytochrome P450 mixed-function oxidase system which is involved in the metabolism of xenobiotics in the body. While CYP2E1 is implicated in the oxidative metabolism of small range substrates, commonly small polar molecules, there are many significant drug interactions which are mediated by CYP2E1.

Cytochrome P450 2D6 is a member of a complex family of microsomal enzymes (mono-oxygenases) present in the endoplasmic reticulum membrane, which perform detoxification reaction on xenobiotic compounds. Cytochrome P450 2D6 is the molecular target of autoantibodies against the "liver kidney microsomal antigen 1" (LKM 1) which has been classically defined by immunofluorescence microscopy. The presence of these autoantibodies is considered indicative of Autoimmune Hepatitis Type 2; LKM 1 antibodies have also been detected in patients with hepatitis C viral infection. The International Autoimmune Hepatitis Group therefore has subdivided the AIH type 2 into two subgroups: 2a with HCV and 2b without HCV. AIH 2a patients are often over 40 and predominantly male.
The use of a purified recombinant Cytochrome P450 2D6 antigen allows the differentiation of autoimmune hepatitis from drug-induced hepatitis where transient autoantibodies to other P450 family members occur which cannot be differentiated by immunofluorescence techniques.

CYB5R3 is a cytochrome b5 reductase, which includes a membrane-bound form in somatic cells (anchored in the endoplasmic reticulum, mitochondrial and other membranes) and a soluble form in erythrocytes. The membrane-bound form exists mainly on the cytoplasmic side of the endoplasmic reticulum and functions in desaturation and elongation of fatty acids, in cholesterol biosynthesis, and in drug metabolism. The erythrocyte form is located in a soluble fraction of circulating erythrocytes and is involved in methemoglobin reduction. The membrane-bound form has both membrane-binding and catalytic domains, while the soluble form has only the catalytic domain. Mutations in this gene cause methemoglobinemias.

Cytochrome b5 isoform 1 or CYB5A, is part of the cytochrome b5 family which is bound to the cell membrane. CYB5A has a key role in the stearyl-CoA-desaturase activity as it reduces ferric hemoglobin to ferrous hemoglobin. Cytochrome b5 isoform 1 performs as an electron carrier for numerous oxygenases that are imbedded in the cell membrane.

Cytochrome b5 isoform 1 (CYB5A) is a member of the cytochrome b5 family. CYB5A is a membrane bound hemoprotein which functions as an electron carrier for several membrane bound oxygenases. Defects in the CYB5A gene are the cause of methemoglobinemia CYB5A-related (METHB-CYB5A), which is a form of methemoglobinemia (a hematologic disease characterized by the presence of excessive amounts of methemoglobin in blood cells, resulting in decreased oxygen carrying capacity of the blood, cyanosis and hypoxia).