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3.D.10.1.7
Succinate dehydrogenase complex, or succinate:ubiquinone oxidoreductase (SQR) or  mitochondrial respiratory complex II of four subunits, SdhA, B, C and D.  Does not transport protons across the membrane, but all 4 subunits are homologous to the prokaryotic Sdh subunits that do transport protons.  It is an integral membrane protein complex in both the tricarboxylic acid cycle and aerobic respiration. Sun et al. 2005 reported the first crystal structure of Complex II from porcine heart at 2.4 Å resolution and its complex structure with inhibitors 3-nitropropionate and 2-thenoyltrifluoroacetone (TTFA) at 3.5 Å resolution. Complex II is comprised of two hydrophilic proteins, flavoprotein (Fp) and iron-sulfur protein (Ip), and two transmembrane proteins (CybL and CybS), as well as prosthetic groups required for electron transfer from succinate to ubiquinone. The structure correlates the protein environments around prosthetic groups with their unique midpoint redox potentials. Two ubiquinone binding sites are identified. The structure provides a bona fide model for study of the mitochondrial respiratory system and human mitochondrial diseases related to mutations in this complex (Sun et al. 2005).

Accession Number:O14521
Protein Name:Succinate dehydrogenase [ubiquinone] cytochrome b small subunit, mitochondrial
Length:159
Molecular Weight:17043.00
Species:Homo sapiens (Human) [9606]
Number of TMSs:2
Location1 / Topology2 / Orientation3: Mitochondrion inner membrane1 / Multi-pass membrane protein2
Substrate

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FASTA formatted sequence
1:	MAVLWRLSAV CGALGGRALL LRTPVVRPAH ISAFLQDRPI PEWCGVQHIH LSPSHHSGSK 
61:	AASLHWTSER VVSVLLLGLL PAAYLNPCSA MDYSLAAALT LHGHWGLGQV VTDYVHGDAL 
121:	QKAAKAGLLA LSALTFAGLC YFNYHDVGIC KAVAMLWKL