COX5B

Cytochrome c oxidase subunit 5B, mitochondrial is an enzyme in humans that is a subunit of the cytochrome c oxidase complex, also known as Complex IV, the last enzyme in the mitochondrial electron transport chain. In humans, cytochrome c oxidase subunit 5B is encoded by the COX5B gene.

Structure
The enzyme weighs 14 kDa and is composed of 129 amino acids. The protein is a subunit of Complex IV, which consists of 13 mitochondrial- and nuclear-encoded subunits. The sequence of subunit Vb is well conserved and includes three conserved cysteines that coordinate the zinc ion. Two of these cysteines are clustered in the C-terminal section of the subunit.

Gene
The COX5B gene, located on the q arm of chromosome 2 in position 11.2, is made up of 4 exons and is 2,137 base pairs in length.

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 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 and COX5B are involved in the regulation of cancer cell metabolism by Bcl-2.

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.

Interactions
COX5B has been shown to interact with Androgen receptor.