Description
SS-31 Research Peptide (10 mg)
SS-31, also known by its INN elamipretide and development designation MTP-131, is a synthetic aromatic-cationic tetrapeptide belonging to the Szeto-Schiller (SS) peptide family. It is one of the most extensively characterized mitochondria-targeting peptides in the preclinical research literature, with a mechanism of action centered on direct interaction with the inner mitochondrial membrane phospholipid cardiolipin.
SS-31 has been characterized across a broad body of peer-reviewed in-vitro and in-vivo research examining mitochondrial membrane biophysics, electron transport chain function, oxidative stress attenuation, and cytoprotection in models of ischemia-reperfusion injury, neurodegeneration, cardiac dysfunction, and cellular aging. Its ability to selectively concentrate in the inner mitochondrial membrane without requiring a membrane potential gradient distinguishes it from earlier mitochondria-targeting cationic compounds.
Structural Characteristics
SS-31 has the sequence D-Arg-Dmt-Lys-Phe-NH₂, where Dmt denotes 2′,6′-dimethyltyrosine—a non-natural aromatic amino acid incorporated at position 2. The peptide alternates aromatic and cationic residues in a defined pattern (cationic-aromatic-cationic-aromatic) that has been identified as critical for both cell penetration and inner mitochondrial membrane partitioning.
The N-terminal D-arginine confers resistance to aminopeptidase cleavage, while the C-terminal phenylalanine amide resists carboxypeptidase activity, together providing proteolytic stability in biological matrices. The dimethyltyrosine residue introduces steric bulk that increases membrane affinity and electron-donating capacity relative to native tyrosine, enhancing the peptide’s interactions with the polyunsaturated acyl chains of cardiolipin. SS-31’s net charge of +3 at physiological pH facilitates electrostatic interactions with negatively charged membrane phospholipids without requiring the large transmembrane potential gradient necessary for triphenylphosphonium (TPP)-conjugated mitochondrial targeting agents.
Characterized Signaling Pathways
Published research has identified multiple mechanistic interactions at the mitochondrial and cellular level:
Cardiolipin Binding and Inner Mitochondrial Membrane Stabilization
SS-31 selectively binds cardiolipin (CL), a dimeric phospholipid uniquely enriched in the inner mitochondrial membrane (IMM) and essential for organizing electron transport chain (ETC) supercomplexes. Biophysical studies using solid-state NMR and fluorescence spectroscopy demonstrated that SS-31 intercalates into CL-rich membrane domains, reducing peroxidation of CL’s polyunsaturated acyl chains and preserving the curvature and fluidity of the IMM required for efficient ETC supercomplex assembly (Birk et al., Cell Death and Disease, 2013; Szeto, Antioxidants & Redox Signaling, 2014).
Electron Transport Chain Supercomplex Preservation and ATP Synthesis
By stabilizing CL and the IMM, SS-31 promotes the assembly and stability of ETC supercomplexes (respirasomes), which channel electrons efficiently through Complexes I, III, and IV while minimizing electron leak to molecular oxygen. Studies in isolated mitochondria and intact cell models demonstrated that SS-31 treatment restores Complex I and Complex IV activity, increases oxygen consumption rate (OCR), and enhances ATP production under conditions of oxidative stress or ischemic injury (Szeto & Schiller, Pharmaceutical Research, 2011).
Mitochondrial ROS Attenuation and Superoxide Suppression
SS-31’s aromatic residues (Dmt and Phe) confer electron-scavenging capacity, enabling the peptide to directly quench mitochondria-generated reactive oxygen species (ROS) at the site of production. This activity is mechanistically distinct from—and complementary to—its cardiolipin-stabilizing function. Studies using mitochondrial superoxide indicators (MitoSOX) confirmed that SS-31 reduces mitochondrial superoxide generation in models of ischemia-reperfusion, drug-induced mitochondrial toxicity, and age-associated oxidative stress (Zhao et al., Journal of the American Chemical Society, 2004).
Cytochrome c Retention and Apoptosis Pathway Modulation
Cardiolipin peroxidation is a critical early event in the release of cytochrome c from the IMM into the mitochondrial intermembrane space, a committed step toward caspase activation and intrinsic apoptosis. By inhibiting CL peroxidation, SS-31 reduces cytochrome c dissociation from the IMM and limits downstream caspase-3/9 activation in cell models of mitochondrial stress, providing a tool for investigating the cardiolipin–cytochrome c–apoptosis signaling axis (Birk et al., Journal of Molecular and Cellular Cardiology, 2014).
Research Applications
SS-31 has been utilized as a molecular probe in controlled experimental systems examining:
- Cardiolipin biophysics and inner mitochondrial membrane integrity
- Electron transport chain supercomplex assembly and stability
- Mitochondrial ROS generation and antioxidant signaling
- Ischemia-reperfusion injury models (cardiac, renal, cerebral)
- Mitochondrial apoptosis pathway and cytochrome c release
- Neurodegenerative disease mitochondrial dysfunction models
- Skeletal muscle mitochondrial bioenergetics and aging research
