SS-31: Mitochondrial-Targeted Tetrapeptide Research Overview

SS-31 was developed by Hazel Szeto and Peter Schiller in the early 2000s as part of a class of peptides designed to specifically target the inner mitochondrial membrane. The Szeto-Schiller class peptides share a structural feature — alternating aromatic and basic residues — that promotes electrostatic attraction to negatively charged cardiolipin on the inner mitochondrial membrane.^[1]

Cardiolipin is a unique mitochondrial phospholipid concentrated on the inner membrane where it interacts with electron transport chain complexes. Disruption of cardiolipin organization is associated with mitochondrial dysfunction in many disease models, making cardiolipin-binding compounds like SS-31 useful research tools.^[2]

SS-31 is studied as a research reference compound. While clinical trials have explored therapeutic applications, research-grade material is supplied for laboratory research only.

SS-31 structural features:

• Sequence: D-Arg-2'6'-dimethylTyrosine-Lys-Phe-NH₂ (4 residues with non-natural amino acids)

• Notable feature: alternating aromatic-basic residue pattern characteristic of Szeto-Schiller peptides

• Charge: +3 at physiological pH (one Arg, one Lys, plus N-terminus)

• Molecular weight: approximately 640 Da

• C-terminus: amidated

Despite its net positive charge, SS-31 is cell-permeant — it crosses plasma membranes and accumulates in mitochondria. The mechanism involves the membrane potential of the inner mitochondrial membrane (negative inside), which attracts the positively charged peptide.^[3]

Once at the inner mitochondrial membrane, SS-31 binds cardiolipin via electrostatic interactions with the aromatic residues providing additional membrane interface contacts. The resulting accumulation in mitochondria is selective and concentration-dependent.

SS-31's research-characterized mechanisms center on mitochondrial membrane and electron transport function.

Direct binding of SS-31 to cardiolipin has been characterized in cell-free systems using purified cardiolipin and biophysical measurement techniques (fluorescence, surface plasmon resonance, NMR). The interaction is selective for cardiolipin over other anionic phospholipids.^[3]

SS-31 binding to cardiolipin in the inner mitochondrial membrane is associated with preservation of electron transport chain complex assembly. Preclinical studies have measured complex IV (cytochrome c oxidase) activity and complex I activity in tissues exposed to SS-31 under ischemic or stress conditions.^[4]

Mitochondrial reactive oxygen species (ROS) production has been measured in preparations exposed to SS-31. Preserving electron transport chain integrity reduces electron leak and downstream ROS generation in stress conditions.^[5]

SS-31 research spans several preclinical domains.

Rodent and porcine cardiac ischemia-reperfusion models are among the most-studied SS-31 research preparations. Endpoints include infarct size, cardiac function recovery markers, and mitochondrial function in cardiac tissue.^[4]

Aged rodent models with diminished mitochondrial function have included SS-31 in experimental arms examining muscle, kidney, and other tissue mitochondrial endpoints.^[5]

Acute kidney injury models in animals have examined SS-31 effects on renal tissue mitochondrial function and recovery markers.^[6]

SS-31 is a stable cell-permeant tetrapeptide. Standard peptide handling applies.

Lyophilized SS-31 is stored at minus 20 degrees Celsius. Reconstituted solution is stored at 4 degrees Celsius and used within several weeks.

Bacteriostatic water or sterile water are standard reconstitution solvents.

HPLC for purity, mass spectrometry for identity confirmation matching the modified tetrapeptide structure, and endotoxin screening. Each batch of Instant Peptides SS-31 ships with a full Certificate of Analysis.

Instant Peptides supplies SS-31 as a synthetic lyophilized reference compound. Material is supplied to qualified research professionals. Not for human or animal consumption.

View the product page for current pricing and the Certificate of Analysis for the active batch.