• Prosthetic group features
• Cyt b/b₆ in motif databases
• Cyt b/b₆ in alignment databases
• Cyt b/b₆ in 3­D databases
• References

Centre	Em (mV)	Haem type	Haem iron coordination	Axial iron ligands		Formal iron oxidation/spin states
bH (b560)	+40	Haem b	Hexacoordinate	NHis; NHis		FeII (S=0); FeIII (S=1/2)
bL (b566)	-90

Cytochrome b (cyt b) is one of three redox subunits present in both the cytochrome bc₁ complex (ubiquinol:ferricytochrome c oxidoreductase; EC 1.10.2.2) and the cytochrome b₆f complex (plastoquinol:plastocyanin reductase; EC 1.10.99.1) [1, 2]. Cyt b binds a high­ (b_H; b₅₆₀ or b₅₆₂) and a low­ (b_L; b₅₆₆ or b₅₆₅) potential haem group.

3­D structures of the cyt bc₁ complex from mitochondria have been determined [1 and references therein]. Cyt b contains eight transmembrane helices (A to H) connected by four long loops (AB, CD, DE, EF) and three short loops (BC, FG, GH). The DE loop is on the matrix side, while the remaining three long loops are on the intermembrane space side. The AB and EF loops each contain one helix; the CD loop contains two short helices forming a hairpin structure. Both the N­ and C­termini of cyt b are located in the matrix. The two haems are bound within the four­helix bundle A/B/C/D. In bovine cyt b, the axial ligands for haem b_L are His­83 and His­182, and His­97 and His­196 for haem b_H [3]. These four histidines are absolutely invariant in the sequences of cyt b and b₆ [4].

Cytochrome b/b₆ in motif databases

PRINTS ID	PRINTS AC	PROSITE/BLOCKS ID	PROSITE AC	BLOCKS AC
-	-	CYTOCHROME_B_HEME CYTOCHROME_B_QO	PS00192 PS00193	BL00192

Cytochrome b/b₆ in alignment databases

Protein Superfamily	Protein Homology Domain	Pfam	LPFC 3­D alignment
00019; cytochrome b	00007; 00008; 00188 cytochrome b/ cytochrome b6	PF00033; cytochrome_b_N; PF00032; cytochrome_b_C	-

Cytochrome b/b₆ in 3­D databases

PDB	scop	BSM	RELI Base	Header	¹
1bcc	-	1bcc	-	Cytochrome bc1 complex (complex with ubiquinone­10, phosphatidyl ethanolamine and B­octylglucoside); chicken (heart mitochondrial)	-
1be3	-	1be3	-	Cytochrome bc1 complex; bovine (heart mitochondrial)	-
1bgy	-	1bgy	-	Cytochrome bc1 complex; bovine (heart mitochondrial)	-
1qcr	-	1qcr	-	Cytochrome bc1 complex (C atoms only); bovine (heart mitochondrial)	-
3bcc	-	3bcc	-	Cytochrome bc1 complex (complex with stigmatellin and antimycin); chicken (heart mitochondrial)	-

¹ Macromolecular Structures abstract. Full text is available to BioMedNet Members

References

1. Crofts, A.R. and Berry, E.A. (1998) Structure and function of the cytochrome bc₁ complex of mitochondria and photosynthetic bacteria. Curr. Opin. Struct. Biol. 8, 501-509.
2. Cramer, W.A., Martinez, S.E., Furbacher, P., Huang, D. and Smith, J.L. (1994) The cytochrome b₆f complex. Curr. Opin. Struct. Biol. 4, 536-544.
3. Xia, D., Yu, C.­A., Kim, H., Xia, J.Z., Kachurin, A.M., Zhang, L., Yu, L. and Deisenhofer, J. (1997) Crystal structure of the cytochrome bc₁ complex from bovine heart mitochondria. Science 277, 60-66 [published erratum Science 278, 2037 (1997)].
4. Widger, W.R., Cramer, W.A., Herrmann, R.G. and Trebst, A. (1984) Sequence homology and structural similarity between cytochrome b of mitochondrial complex III and the chloroplast b₆-f complex: Position of the cytochrome b hemes in the membrane. Proc. Natl. Acad. Sci. USA 81, 674-678.

Bibliography on structural studies of cytochrome b/b6 (bHbL)

Bibliography on structural studies of cytochrome bc1 complex

Reviews on cytochrome bc1 complex