Cytochrome C1

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Cytochrome C1
Symbol CYC1
Alt. symbols UQCR4, MC3DN6
Entrez 1537
HUGO 2579
OMIM 123980
RefSeq NM_001916.4
UniProt P08574
Other data
Locus Chr. 8 243

Cytochrome C1 (also known as Complex III subunit 4) is a protein encoded by the CYC1 gene. Cytochrome is a heme-containing subunit of the cytochrome b-c1 complex, which accepts electrons from Rieske protein and transfers electrons to cytochrome c in the mitochondrial respiratory chain.[1] It is formed in the cytosol and targeted to the mitochondrial intermembrane space. Cytochrome c1 belongs to the cytochrome c family of proteins.


Cytochrome C1 plays a role in the electron transfer during oxidative phosphorylation. As an iron-sulfur protein approaches the b-c1 complex, it accepts an electron from the cytochrome b subunit, then undergoes a conformational change to attach to cytochrome c1. There, the electron carried by the iron-sulfur protein is transferred to the heme carried by cytochrome c1. This electron is then transferred to a heme carried by cytochrome c. This creates a reduced species of cytochrome c, which separates from the b-c1 complex and moves to the last enzyme in the electron transport chain, cytochrome c oxidase (Complex IV).[2]


CYC1 is a human gene that is conserved in chimpanzee, Rhesus monkey, dog, cow, mouse, rat, zebrafish, fruit fly, mosquito, C. elegans, S. cerevisiae, K. lactis, E. gossypii, S. pombe, M. oryzae, N. crassa, A. thaliana, rice, and frog.[3] There are orthologs of CYC1 in 137 known organisms.[4]

In its structure and function, the cytochrome b-c1 complex bears extensive analogy to the cytochrome b6f complex of chloroplasts and cyanobacteria; cytochrome c1 plays an analogous role to cytochrome f, despite their different structures.[5]

Clinical relevance[edit]

Mutations in the CYC1 gene are associated with mitochondrial complex III deficiency nuclear type 6. The disease symptoms include early childhood onset of severe lactic acidosis and ketoacidosis, usually in response to infection. Insulin-responsive hyperglycemia is also present, but psychomotor development appears normal. Mutation of CYC1 was observed to cause instability in the cytochrome b-c1 complex, which decreased its ability to create energy through oxidative phosphorylation.[6] Mitochondrial complex III deficiency nuclear type 6 is autosomal recessive.[7]

External links[edit]


  1. ^ "CYC1 - Cytochrome c1, heme protein, mitochondrial precursor - Homo sapiens (Human) - CYC1 gene & protein". Retrieved 2016-07-29. 
  2. ^ Kokhan, Oleksandr; Wraight, Colin A.; Tajkhorshid, Emad (2010-10-20). "The Binding Interface of Cytochrome c and Cytochrome c1 in the bc1 Complex: Rationalizing the Role of Key Residues". Biophysical Journal. 99 (8): 2647–2656. ISSN 0006-3495. PMC 2955499Freely accessible. PMID 20959106. doi:10.1016/j.bpj.2010.08.042. 
  3. ^ "CYC1 cytochrome c1 [Homo sapiens (human)]". National Center for Biotechnology Information. U.S. National Library of Medicine. Retrieved 2016-07-29. 
  4. ^ "ortholog_gene_1537[group]". National Center for Biotechnology Information. U.S. National Library of Medicine. Retrieved 2016-07-29. 
  5. ^ Prince, Roger C.; George, Graham N. (1995). "Cytochrome f revealed". Trends in Biochemical Sciences. 20 (6): 217–8. PMID 7631417. doi:10.1016/S0968-0004(00)89018-0. 
  6. ^ "CYTOCHROME C1; CYC1". Online Mendelian Inheritance in Man. Johns Hopkins University. 2 Oct 2013. Retrieved 2016-07-29. 
  7. ^ "OMIM Gene Map". Online Mendelian Inheritance in Man. Johns Hopkins University. Retrieved 2016-07-29. 

This article incorporates text from the public domain Pfam and InterPro IPR002326