Peptide directoryBone, muscle & mineral

BRAWNIN

A micropeptide needed to assemble complex III of the respiratory chain.

Where it comes from

Made in
Every tissue that respires, most in muscle and heart
Sent out by
Not secreted
Acts on
  • Complex III (ubiquinol-cytochrome c reductase) assembly

What it does

  • Without it complex III is not assembled and cells cannot respire properly 1
  • Induced by AMPK when energy is low
  • Zebrafish without it lose complex III entirely, grow poorly and die early 1

In medicine

  • No medicine acts on it, and no patient has yet been reported with a damaging change in its gene
  • It is on the candidate list for unexplained complex III deficiency, the mitochondrial disease that matches what losing it does to a fish; a gene panel that includes it would be a research panel 1

Beyond the body’s own use

  • The finding is disputed. A 2024 study knocked it down in human cells and found complex III assembled almost normally, so how far the zebrafish result carries into people is open 2
  • What is being asked next is whether its job is to help build complex III or to hold it steady once built, and whether human cells have something else that covers for it 12
  • Nothing about it has been tested in a person. There is nothing to take and no claim made for it outside the laboratory

Sources

  1. Zhang et al., Mitochondrial peptide BRAWNIN is essential for vertebrate respiratory complex III assembly, Nature Communications 2020
  2. Wang et al., Knockdown of BRAWNIN minimally affects complex III assembly in human cells, BBA Molecular Cell Research 2024

This card describes what a medicine is for and what the evidence says; it recommends nothing. Talk to your clinician about anything you read here.