Humanin is unusual in its origin: it is encoded not in the nuclear genome but within the mitochondrial 16S ribosomal RNA gene, making it one of the first described mitochondrial-derived peptides. The supplied 24-residue sequence corresponds to the human form. It was identified through its ability to protect neuronal cells from insults associated with Alzheimer's disease, and subsequent work established that it acts on intracellular signalling rather than simply buffering damage. Humanin has been reported to activate the ERK1/2, AKT and STAT3 pathways, with signalling differences that depend on age in the hippocampus, and it is studied more broadly as a suppressor of apoptosis in a range of cell types. That has placed it within a growing interest in peptides encoded by the mitochondrial genome as signalling molecules in their own right. One handling point deserves attention. The sequence contains a single cysteine, so the peptide can form disulfide-linked dimers on storage in oxidising conditions, and preparations differ in whether that has occurred. Where reproducibility matters, check the oxidation state rather than assuming a monomeric starting material, and prepare stocks fresh where possible. | 