Cytochrome C1 (also known as Complex III subunit 4) is a protein encoded by the ''

CYC1 Cytochrome c1, heme protein, mitochondrial (CYC1), also known as UQCR4, MC3DN6, Complex III subunit 4, Cytochrome b-c1 complex subunit 4, or Ubiquinol-cytochrome-c reductase complex cytochrome c1 subunit is a protein that in humans is encoded by t ...

'' gene. Cytochrome is a

heme Heme, or haem (pronounced / hi:m/ ), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. In biochemical terms, heme is a coordination complex "consis ...

-containing subunit of the cytochrome b-c1 complex, which accepts electrons from

Rieske protein Rieske proteins are iron–sulfur protein (ISP) components of cytochrome ''bc''1 complexes and cytochrome b6f complexes and are responsible for electron transfer in some biological systems. John S. Rieske and co-workers first discovered the pro ...

and transfers electrons to cytochrome c in the

mitochondrial respiratory chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples thi ...

. It is formed in the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

and targeted to the

mitochondrial intermembrane space A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...

. Cytochrome c1 belongs to the

cytochrome c family Cytochromes ''c'' (cyt ''c'', c-type cytochromes) cytochromes, or heme-containing proteins, that have heme C covalently attached to the peptide backbone via one or two thioether bonds. These bonds are in most cases part of a specific Cys-X-X-Cy ...

of proteins.

Function

Cytochrome C1 plays a role in the

electron transfer Electron transfer (ET) occurs when an electron relocates from an atom or molecule to another such chemical entity. ET is a mechanistic description of certain kinds of redox reactions involving transfer of electrons. Electrochemical processes ar ...

during oxidative phosphorylation. As an

iron-sulfur protein Iron–sulfur proteins (or iron–sulphur proteins in British spelling) are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur cl ...

approaches the b-c1 complex, it accepts an electron from the

cytochrome b Cytochrome b within both molecular and cell biology, is a protein found in the mitochondria of eukaryotic cells. It functions as part of the electron transport chain and is the main subunit of transmembrane cytochrome bc1 and b6f complexes. F ...

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 The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory elect ...

(Complex IV).

Species

''CYC1'' is a human gene that is conserved in chimpanzee, Rhesus monkey, dog, cow, mouse, rat,

zebrafish The zebrafish (''Danio rerio'') is a freshwater fish belonging to the minnow family (Cyprinidae) of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio (and thus often ca ...

, fruit fly, mosquito, ''C. elegans'', '' S. cerevisiae,'' '' K. lactis'', '' E. gossypii'', ''

S. pombe ''Schizosaccharomyces pombe'', also called "fission yeast", is a species of yeast used in traditional brewing and as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped. Cells typically measur ...

'', ''

N. crassa ''Neurospora crassa'' is a type of red bread mold of the phylum Ascomycota. The genus name, meaning "nerve spore" in Greek, refers to the characteristic striations on the spores. The first published account of this fungus was from an infestation ...

'', '' A. thaliana'', rice, and frog. There are

orthologs Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a sp ...

of CYC1 in 137 known organisms. In its structure and function, the cytochrome b-c1 complex bears extensive analogy to the

cytochrome b6f complex The cytochrome ''b''6''f'' complex (plastoquinol—plastocyanin reductase; ) is an enzyme found in the thylakoid membrane in chloroplasts of plants, cyanobacteria, and green algae, that catalyzes the transfer of electrons from plastoquinol ...

of chloroplasts and cyanobacteria; cytochrome c1 plays an analogous role to

cytochrome f Cytochrome ''f'' is the largest subunit of cytochrome ''b''6''f'' complex (plastoquinol—plastocyanin reductase; ). In its structure and functions, the cytochrome b6f complex bears extensive analogy to the cytochrome bc1 complex of mitochondr ...

, despite their different structures.

Clinical relevance

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 Lactic acidosis is a medical condition characterized by a build-up of lactate (especially -lactate) in the body, with formation of an excessively low pH in the bloodstream. It is a form of metabolic acidosis, in which excessive acid accumulates d ...

and

ketoacidosis Ketoacidosis is a metabolic state caused by uncontrolled production of ketone bodies that cause a metabolic acidosis. While ketosis refers to any elevation of blood ketones, ketoacidosis is a specific pathologic condition that results in changes ...

, 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. Mitochondrial complex III deficiency nuclear type 6 is autosomal recessive.

References

External links

* {{Electron transport chain Transmembrane proteins Cellular respiration