Protein-coding gene in the species Homo sapiens
Cytochrome "c" oxidase subunit 5a is a protein that in humans is encoded by the COX5A gene. Cytochrome "c" oxidase 5A is a subunit of the cytochrome c oxidase complex, also known as Complex IV, the last enzyme in the mitochondrial electron transport chain.
Structure.
The COX5A gene, located on the q arm of chromosome 15 in position 24.1, is made up of 5 exons and is 17,880 base pairs in length. The COX5A protein weighs 17 kDa and is composed of 150 amino acids. The protein is a subunit of Complex IV, which consists of 13 mitochondrial- and nuclear-encoded subunits.
Function.
Cytochrome "c" oxidase (COX) is the terminal enzyme of the mitochondrial respiratory chain. It is a multi-subunit enzyme complex that couples the transfer of electrons from cytochrome "c" to molecular oxygen and contributes to a proton electrochemical gradient across the inner mitochondrial membrane to drive ATP synthesis via protonmotive force. The mitochondrially-encoded subunits perform the electron transfer of proton pumping activities. The functions of the nuclear-encoded subunits are unknown but they may play a role in the regulation and assembly of the complex.
Summary reaction:
 4 Fe2+-cytochrome "c" + 8 H+in + O2 → 4 Fe3+-cytochrome "c" + 2 H2O + 4 H+out
Clinical significance.
COX5A (this gene) and COX5B are involved in the regulation of cancer cell metabolism by Bcl-2. COX5A interacts specifically with Bcl-2, but not with other members of the Bcl-2 family, such as Bcl-xL, Bax or Bak.
The "Trans"-activator of transcription protein (Tat) of human immunodeficiency virus (HIV) inhibits cytochrome "c" oxidase (COX) activity in permeabilized mitochondria isolated from both mouse and human liver, heart, and brain samples.
References.
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Further reading.
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External links.
"This article incorporates text from the United States National Library of Medicine, which is in the public domain."