SS-31 complete guide

SS-31 — chemically D-Arg-2,6-dimethyl-Tyr-Lys-Phe-NH₂, also known as elamipretide, MTP-131 or Bendavia — is the most-studied compound in the Szeto-Schiller tetrapeptide series. The “SS” designation refers to Hazel Szeto and Peter Schiller, who developed the series at Cornell University; SS-31 was the 31st compound in their iterative tetrapeptide design programme. It has subsequently become the canonical reference molecule for the mitochondrial-targeted aromatic-cationic peptide class, with several hundred published research-animal studies and an active translational programme run by Stealth BioTherapeutics under the elamipretide name.

What makes SS-31 mechanistically distinct from every other peptide in the longevity research literature is its target. Where most peptides act on receptors — cell-surface or intracellular protein receptors — SS-31 acts on a lipid: it binds cardiolipin in the inner mitochondrial membrane directly, without any protein intermediary. This places SS-31 in a rare mechanism class that is best described as membrane pharmacology rather than receptor pharmacology, and the targeting selectivity is a piece of elegant medicinal chemistry: a four-residue peptide that selectively concentrates roughly 1,000–5,000-fold inside mitochondria. Stealth BioTherapeutics has carried elamipretide into clinical-trial development for primary mitochondrial myopathy and Barth syndrome, making SS-31 one of the very few research peptides that has bridged into a translational pipeline.

Quick reference — SS-31 identifiers

Property	SS-31
Class	Aromatic-cationic tetrapeptide, Szeto-Schiller series, mitochondrial-targeted
Sequence	D-Arg-2,6-dimethyl-Tyr-Lys-Phe-NH2 (D-amino acid + dimethylated tyrosine + C-terminal amide)
Other names	Elamipretide, MTP-131, Bendavia, Stealth peptide SS-31
Molecular formula	C32H49N9O5
Molecular weight	639.79 g/mol
CAS	736992-21-5
Origin	Synthetic small peptide, designed by Szeto and Schiller at Cornell University
Plasma half-life	Research models: ~2 hours
Vial strengths (TogoPeptide)	5 mg lyophilized; also part of the Longevity Stack bundle

Origin and structure — Szeto-Schiller mitochondrial-targeted peptide

Reaching the inner mitochondrial membrane with a therapeutic agent is a non-trivial pharmacological problem. The outer mitochondrial membrane is a relatively permissive barrier, but the intermembrane space and the inner mitochondrial membrane are tightly regulated, and the matrix is one of the most isolated compartments in eukaryotic biology. Most small molecules cannot reach the inner-membrane phase in useful concentrations. The Szeto-Schiller series was designed to solve this problem with a specific structural motif rather than by relying on conjugation to a delivery vehicle.

The motif is an alternating aromatic and basic residue pattern on a four-residue backbone. SS-31 specifically uses D-arginine (basic, D-amino acid for protease resistance), 2,6-dimethyltyrosine (aromatic, dimethylated to block phenol oxidation), lysine (basic), and phenylalanine (aromatic), all capped with a C-terminal amide. The D-amino-acid backbone modification confers protease resistance — SS-31 is highly stable to peptidase degradation in plasma. The aromatic-cationic alternation produces a peptide that is membrane-active but not membrane-disruptive: it partitions into mitochondrial membranes selectively without permeabilising them.

The result is a four-residue peptide of 639.79 g/mol that, in published research-cell-model work, accumulates in mitochondria at concentrations roughly 1,000–5,000-fold higher than in cytosol. The selectivity is intrinsic to the chemistry — no targeting peptide tag, no lipophilic-cation conjugation, just the alternating aromatic-cationic structural motif.

Mechanism — cardiolipin binding and cristae stabilization

SS-31 has one mechanistically central interaction: it binds cardiolipin in the inner mitochondrial membrane. Every documented downstream effect — cristae preservation, reduced ROS generation, cytochrome c protection — is a consequence of this single lipid-binding event.

Cardiolipin biology

Cardiolipin is a structurally unusual phospholipid. Where most phospholipids carry two fatty-acid chains, cardiolipin (technically diphosphatidylglycerol) carries four fatty-acid chains attached through a central glycerol bridge between two phosphatidyl head groups. It is found almost exclusively in the inner mitochondrial membrane and represents roughly 15–20% of the inner-membrane lipid content. Its functions are structural and organisational rather than primarily metabolic:

• Cardiolipin organises cristae morphology — the characteristic folded inner-membrane structure that defines mitochondria.
• Cardiolipin stabilises the electron-transport-chain complexes (Complexes I, III, IV) and the supercomplex assemblies that increase ETC efficiency.
• Cardiolipin binds cytochrome c at the outer leaflet of the inner membrane — the binding interaction whose disruption initiates intrinsic apoptosis.
• Cardiolipin oxidation and remodelling drive a wide set of mitochondrial-dysfunction phenotypes documented across cardiac, renal, neuronal and skeletal-muscle research-animal models.

SS-31 binding to cardiolipin

Published research documents SS-31 binding cardiolipin selectively in the inner mitochondrial membrane [2]. The binding interface uses the alternating aromatic-cationic pattern of the SS-31 sequence interacting with cardiolipin’s negatively-charged phosphate head groups (cationic-anionic electrostatic component) and with the glycerol bridge and acyl chains (aromatic stacking and hydrophobic component). The interaction is direct, lipid-binding, and crucially does not require any protein receptor. This mechanism distinguishes SS-31 from essentially every other peptide in the longevity research literature.

Cristae structure preservation

Published research-animal-model literature in cardiac, kidney and skeletal-muscle systems documents that SS-31 binding cardiolipin preserves cristae morphology under stress conditions where cristae would otherwise become disorganised [1]. Disorganised cristae are a hallmark of stressed and aged mitochondria visible by electron microscopy. Preserved cristae structure means preserved electron-transport-chain complex organisation, which means preserved ATP synthesis efficiency. The cristae-preservation finding is one of the most robust observations in the SS-31 literature, replicated across multiple stress models and tissue systems.

Reduced reactive-oxygen-species generation

When electron-transport-chain complexes are properly organised within an intact cristae structure, electrons move efficiently through the chain and electron leak (the source of mitochondrial superoxide) is minimised. When cristae become disorganised — which happens under ischemic stress, in aged tissue, in cardiomyopathy models — ETC complex coupling decreases and electron leak rises, producing the well-documented mitochondrial ROS surge. SS-31's cristae-preserving effect therefore reduces the ROS leak that drives oxidative damage. Published research consistently documents reduced mitochondrial ROS in SS-31-treated research models [3]. Importantly, SS-31 is not a chemical antioxidant in the classical sense — it does not directly scavenge ROS; it reduces ROS generation at the source by stabilising the structure that minimises leak.

Cytochrome c protection

Cardiolipin binds cytochrome c at the outer leaflet of the inner mitochondrial membrane. Under stress, cardiolipin can become peroxidised, and the peroxidised cardiolipin–cytochrome c complex acquires peroxidase activity that further oxidises cardiolipin in a feed-forward damage cycle. The eventual release of cytochrome c into the cytosol initiates intrinsic apoptosis. SS-31 binding cardiolipin prevents cardiolipin-cytochrome c peroxidation at this initiating step. Published research documents reduced apoptotic markers and improved mitochondrial-membrane-potential maintenance in stress-model research designs treated with SS-31.

Cardiac research literature

Cardiac tissue is the largest and most studied SS-31 research line. The biology of the heart is highly mitochondrial-dependent (cardiomyocytes derive ~95% of their ATP from oxidative phosphorylation) and cardiac membranes are particularly cardiolipin-rich. Published research-animal-model literature documents SS-31 effects across multiple cardiac stress models:

• Ischemia-reperfusion injury research — preserved mitochondrial function, reduced infarct size and improved post-reperfusion contractile recovery in rodent and porcine cardiac-ischemia models.
• Heart-failure models — preserved cardiolipin composition, reduced cristae disorganisation and improved ATP-synthesis capacity in pressure-overload and genetic-cardiomyopathy designs.
• Doxorubicin cardiotoxicity research — protection against the cardiolipin-peroxidation phenotype that drives anthracycline-induced cardiotoxicity.

The Stealth BioTherapeutics clinical-translational programme extended this published research-animal foundation into human clinical-trial-stage work under the elamipretide name, exploring cardiac and mitochondrial-disease indications. The clinical-trial pipeline status changes over time and is documented in the regulatory record by the sponsor — references in this article describe the published peer-reviewed research-stage literature and the clinical-trial-stage research designs only.

Mitochondrial myopathy research

The other major SS-31 research line concerns primary mitochondrial myopathy and related genetic mitochondrial diseases, including Barth syndrome — an X-linked disorder of cardiolipin remodelling caused by mutations in the TAZ (tafazzin) gene that produces dilated cardiomyopathy and skeletal-muscle weakness. The mechanistic logic is direct: Barth syndrome is fundamentally a cardiolipin-deficiency disorder, and a compound that binds and stabilises remaining cardiolipin is a logical research candidate. The Karaa et al. dose-escalation study published in Neurology represents one of the more advanced clinical-translational stages reached by any compound in the longevity-adjacent peptide research space [6].

This translational arc — published preclinical research-animal models, then sponsor-led clinical-trial-stage research — is unusual for a longevity-peptide research compound and is one of the reasons SS-31 occupies a particular position in the field’s attention.

Renal and aging-tissue research

Beyond cardiac and mitochondrial-myopathy lines, published research-animal-model literature documents SS-31 effects in:

• Renal aging research — oxidative-damage models, ischemia-reperfusion kidney injury, and age-related renal-function decline designs, where cristae preservation and reduced mitochondrial ROS map onto preserved tubular function.
• Skeletal-muscle aging / sarcopenia research — published research-animal models of age-related muscle decline document preserved mitochondrial function and exercise capacity with SS-31 treatment.
• Cardiolipin biology in heart-failure context — the cardiolipin-remodelling literature has expanded substantially, with parallel research on the role of dysregulated cardiolipin biosynthesis in pediatric and adult heart failure [5].
• Neuroprotective research — the Szeto laboratory and others have explored mitochondrial-targeted antioxidant peptides in neurodegeneration and ischemic stroke models [4].

SS-31 vs NAD+ vs MOTS-c — three mitochondrial-research mechanisms

The TogoPeptide Longevity Stack pairs SS-31 with NAD+ and MOTS-c (and Epithalon) precisely because the three mitochondrial-axis compounds operate through fully non-overlapping mechanisms. They sit at distinct nodes of the mitochondrial-aging research conversation:

Compound	Mechanism class	Target	Research line
NAD+	Coenzyme / substrate	Sirtuin / PARP / CD38 enzymes	Sirtuin pathway, age-related decline
MOTS-c	Mitokine signalling peptide	AMPK pathway	Metabolic homeostasis, exercise mimetic
SS-31	Lipid-binding tetrapeptide	Cardiolipin (inner mitochondrial membrane)	Cristae stabilisation, cardiac / myopathy research

Three non-overlapping mitochondrial-aging mechanisms: a coenzyme substrate, a signalling mitokine, and a structural lipid-binder. That is the rationale for combining all three in a single research design — each compound addresses a different axis of mitochondrial-aging biology that the others do not touch.

Storage and handling

SS-31 ships as lyophilized powder, typically white to off-white. Standard research-handling literature documents:

• Lyophilized state: sealed at −20°C, protected from light. The D-amino-acid backbone and the dimethylated tyrosine confer good stability to the lyophilized solid.
• Diluent: bacteriostatic water (0.9% benzyl alcohol) is the standard reconstitution diluent. SS-31 is freely water-soluble.
• Reconstituted state: refrigerate at 2–8°C and protect from light. Approximate 28-day reconstituted shelf life at refrigerator temperature.
• C-terminal amide sensitivity: the C-terminal amide is sensitive to repeated freeze-thaw cycles. Avoid freeze-thaw cycles after reconstitution — aliquot at the time of first reconstitution if multiple use windows are anticipated.
• Light exposure: the dimethyltyrosine and phenylalanine residues are aromatic and photo-active; minimise light exposure during handling.

Each TogoPeptide SS-31 shipment includes a per-batch Certificate of Analysis with HPLC purity, mass-spectrometry identity confirmation, lot number, manufacture date, and analysis date. See how to read a COA or reconstitution methodology for the methodology details.

Cross-research lines and pairings

• Longevity Stack — cellular-aging research bundle: NAD+ + Epithalon + MOTS-c + SS-31 in a curated four-mechanism research design covering coenzyme / sirtuin substrate (NAD+), telomere and gene-expression signalling (Epithalon), AMPK / mitokine signalling (MOTS-c), and cardiolipin / cristae structural stabilisation (SS-31). The four compounds approach the cellular-aging research conversation from four mechanistically non-overlapping angles.
• Reconstitution math: documented in the reconstitution calculator — SS-31 molecular weight (639.79 g/mol) is in the typical small-peptide range, but the 5 mg vial size means volume planning differs from larger vial formats.
• Mitochondrial-axis pairings: some research designs combine SS-31 with NAD+ or MOTS-c to probe orthogonal mitochondrial mechanisms in a single experimental window.

Closing

SS-31 sits in a rare mechanistic class within the peptide research literature. It is a four-residue peptide that, by virtue of an alternating aromatic-cationic structural motif, accumulates selectively in mitochondria and binds cardiolipin in the inner mitochondrial membrane directly — with no protein-receptor intermediary. The cardiolipin interaction stabilises cristae structure, preserves electron-transport-chain organisation, reduces mitochondrial ROS generation at source, and protects against the cardiolipin-cytochrome c peroxidation cascade that initiates intrinsic apoptosis. The cardiac, mitochondrial-myopathy and renal-aging research lines together comprise one of the deepest research portfolios of any peptide in the longevity-adjacent space, and the elamipretide clinical-translational programme makes SS-31 unusual for having bridged from preclinical research-animal models into sponsor-led clinical-trial-stage research.

This guide documents what published peer-reviewed research has investigated. It is mechanism context for laboratory researchers, not therapeutic recommendation, not protocol guidance, not a basis for self-administration of any kind.

Source SS-31 for laboratory research:

• SS-31 product page — full identifiers, 5 mg lyophilized vial, per-batch COA
• Longevity Stack — curated NAD+ + Epithalon + MOTS-c + SS-31 bundle for cellular-aging research designs
• Longevity research compounds — full category listing

For methodology and laboratory-handling questions, contact our research-supply team at info@togopeptide.com.