SS-31 (Elamipretide)

Identity a synthetic tetrapeptide (4 amino acids, < 40 aa → peptide) that carries a positive charge and readily crosses cell membranes to concentrate ~1,000–5,000× inside mitochondria, where it binds the unique inner-membrane phospholipid cardiolipin. One of the most-studied mitochondria-targeting compounds in existence. ## Mechanism (as proposed) SS-31 is a cell-penetrating tetrapeptide that accumulates in mitochondria and binds cardiolipin on the inner mitochondrial membrane. By stabilising cardiolipin, it props up the respiratory-chain supercomplexes (the assembled Complexes I–IV), improving electron-transport efficiency and ATP production while lowering reactive-oxygen-species leak. In Barth syndrome — an X-linked disease where tafazzin mutations cripple cardiolipin remodeling — this directly addresses the molecular root. The exact downstream mechanism beyond cardiolipin binding "remains unclear" (its own mechanistic literature says so), which is part of why it works in the disease built on cardiolipin but repeatedly failed in messier, multifactorial diseases like heart failure.