A mitochondrial protein-coding gene whose product is involved in the respiratory chain
Location of theMT-CYB gene in the human mitochondrial genome (coral box). Cytochrome b is aprotein that in humans is encoded by theMT-CYB gene[ 5] gene product is a subunit of the respiratory chain proteinubiquinol–cytochromec reductase (UQCR, complex III or cytochromebc 1 complex), which consists of the products of one mitochondrially encoded gene,MT-CYB (mitochondrialcytochrome b ), and ten nuclear genes—UQCRC1 UQCRC2 CYC1 UQCRFS1 Rieske protein ),UQCRB UQCRH 1 Hinge protein), Rieske protein presequence, "cyt c1 associated protein", andRieske-associated protein .
TheMT-CYB gene is located on the p arm ofmitochondrial DNA in position 12 and spans 1,140 base pairs.[ 5] cytochrome b composed of 380amino acids .[ 6] [ 7] Cytochrome b is an integral membrane protein with hydrophobic properties. The catalytic core of the enzyme is composed of eight transmembrane helices, theiron-sulfur protein , andcytochrome c1 .[ 8] Cytochrome b is a fundamental component of the ubiquinol-cytochrome c reductase complex (complex III or cytochrome b-c1 complex) that is part of themitochondrial respiratory chain . The b-c1 complex mediates electron transfer fromubiquinol to cytochrome c.[ 9] mitochondrial genome encoded cytochrome b and ten other nucleus encoded subunits. These subunits include three respiratory subunits (MT-CYB,CYC1 andUQCRFS1 ), two core proteins (UQCRC1 andUQCRC2 ) and six low-molecular weight proteins (UQCRH /QCR6 ,UQCRB /QCR7 ,UQCRQ /QCR8 ,UQCR10 /QCR9 ,UQCR11 /QCR10 and a cleavage product ofUQCRFS1 ). The totalmolecular mass of the complex is about 450 kDa.[ 10] [ 9]
The mitochondrialcytochrome b is fundamental for the assembly and function of Complex III of themitochondrial respiratory chain .[ 11] catalysis of electron transfer fromcoenzyme Q tocytochrome c in themitochondrial respiratory chain by translocating protons concomitantly across theinner membrane of the mitochondria .[ 12] [ 9] proton gradient across themitochondrial membrane that is then used for ATP synthesis.[ 9]
Clinical significance [ edit ] Mutations inMT-CYB can result in mitochondrial deficiencies and associated disorders. It is majorly associated with a complex III deficiency, a deficiency in an enzyme complex which catalyzes electron transfer fromcoenzyme Q tocytochrome c in themitochondrial respiratory chain . A complex III deficiency can result in a highly variable phenotype depending on which tissues are affected.[ 9] exercise intolerance andcardiomyopathy . Occasional multisystem disorders accompanied by exercise intolerance may arise as well, in forms ofdeafness ,mental retardation ,retinitis pigmentosa ,cataract ,growth retardation , andepilepsy .[ 9] encephalomyopathy ,mitochondrial myopathy ,Leber hereditary optic neuropathy ,muscle weakness ,myoglobinuria ,blood acidosis , renaltubulopathy , and more.[ 9] [ 10] mitochondrial diseases and may follow amaternal ormendelian mode of inheritance due to its duality of genetic origin.[ 8]
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