SS-31 vs Elamipretide — What's the Real Difference?

SS-31 and elamipretide are the exact same peptide. Not two similar compounds, not analogues, not variations. The name changed when Stealth BioTherapeutics acquired the compound and advanced it from preclinical research into Phase II and Phase III clinical trials. This isn't uncommon: research peptides carry lab designations (SS-31, BPC-157, TB-500) until a pharmaceutical sponsor assigns a formal International Nonproprietary Name (INN) for regulatory filings. Elamipretide is the INN; SS-31 was the original research code from the laboratory at Cornell where the tetrapeptide was first synthesized in the early 2000s.

Our team has worked with researchers using both nomenclatures across mitochondrial function studies, and the confusion is real. Some publications cite SS-31, others elamipretide, and without knowing they reference the same molecule, literature reviews become unnecessarily fragmented. Here's what every researcher working with mitochondrial-targeting peptides needs to understand about this compound, its mechanism, and why the dual naming persists.

What's the difference between SS-31 and elamipretide?

There is no molecular difference between SS-31 and elamipretide. They are the same tetrapeptide with the amino acid sequence D-Arg-Dmt-Lys-Phe-NH2. SS-31 was the original research designation assigned at Cornell's Weill Medical College; elamipretide is the formal drug name adopted when Stealth BioTherapeutics advanced the compound into clinical trials. Both names refer to a mitochondria-targeting peptide that binds to cardiolipin in the inner mitochondrial membrane to stabilize cristae architecture and reduce reactive oxygen species production.

The naming convention reflects the peptide's development trajectory. Not a chemical distinction. When you see SS-31 cited in a 2010 Nature paper and elamipretide in a 2020 JAMA Cardiology trial, you're reading about the exact same compound tested at different stages of its clinical evolution. The amino acid sequence, molecular weight (640.77 g/mol), and cardiolipin-binding mechanism remain identical across every study published under either name. This matters because researchers comparing efficacy data need to recognize that a meta-analysis combining SS-31 and elamipretide studies isn't mixing compounds. It's tracking one molecule's progression from bench science to bedside application.

The Molecular Identity Behind Both Names

Elamipretide (SS-31) is a synthetic tetrapeptide composed of four amino acids: D-arginine, dimethyltyrosine (Dmt), lysine, and phenylalanine, with an amide cap at the C-terminus. The D-arginine at position one is non-natural (the D-enantiomer rather than the L-form found in biological proteins), which confers resistance to peptidase degradation. Standard L-amino acid peptides would be cleaved within minutes in serum. The dimethyltyrosine at position two is another synthetic modification that enhances membrane permeability and prevents enzymatic breakdown by tyrosine hydroxylase.

The peptide's defining characteristic is its high affinity for cardiolipin, a phospholipid found almost exclusively in the inner mitochondrial membrane where it comprises roughly 20% of total lipid content. Cardiolipin plays a structural role in organizing respiratory chain supercomplexes. The protein assemblies (Complexes I, III, and IV) that drive oxidative phosphorylation. When cardiolipin oxidizes under conditions of mitochondrial stress, cristae architecture collapses, electron transport efficiency drops, and cytochrome c (normally sequestered in cristae) leaks into the cytosol, triggering apoptosis. Elamipretide binds to cardiolipin at a 1:1 molar ratio, preventing peroxidation and stabilizing cristae structure even under oxidative load.

Our experience with peptide sourcing for mitochondrial research consistently shows that suppliers list this compound under both names. Sometimes with the designation 'SS-31 (elamipretide)' to clarify equivalence. The CAS registry number (736992-21-5) is identical for both, which is the definitive molecular identifier researchers should verify when comparing products or cross-referencing studies. Any claim that SS-31 and elamipretide differ in potency, purity, or efficacy reflects supplier inconsistency or synthesis quality. Not a difference in the peptide itself.

Clinical Development and the Name Transition

SS-31 originated in the laboratory of Hazel Szeto at Cornell's Weill Medical College around 2003, where it was part of a series of Szeto-Schiller peptides (hence the 'SS' prefix) designed to target mitochondria without requiring a membrane potential-driven uptake mechanism. Traditional mitochondrial antioxidants like MitoQ rely on the mitochondrial membrane potential to pull positively charged compounds into the matrix. A mechanism that fails when mitochondria are already depolarized by disease. SS-31's design bypassed this limitation: its alternating positive charges (from arginine and lysine) and aromatic residues (from dimethyltyrosine and phenylalanine) allow it to cross lipid bilayers independently of membrane potential, accumulating in mitochondria by binding cardiolipin rather than by electrostatic attraction.

Stealth BioTherapeutics licensed SS-31 in 2006 and initiated the formal INN application process, which resulted in the name 'elamipretide' being assigned by the World Health Organization in 2015. From that point forward, regulatory filings, clinical trial registrations (ClinicalTrials.gov), and FDA communications used elamipretide exclusively, while the academic literature continued citing SS-31 in mechanistic studies referencing earlier work. This created a bifurcated nomenclature: basic science papers discussing mitochondrial bioenergetics still use SS-31, while clinical efficacy trials in Barth syndrome, primary mitochondrial myopathy, and heart failure cite elamipretide.

The peptide advanced through Phase II trials for Barth syndrome (a rare genetic disorder caused by mutations in the tafazzin gene, which encodes the enzyme that remodels cardiolipin). The TAZPOWER trial published in Genetics in Medicine (2019) demonstrated significant improvement in the 6-minute walk test distance. The primary endpoint for exercise capacity in mitochondrial myopathies. Subsequent Phase III trials (MMPOWER-3) did not meet primary endpoints for chronic administration, but acute dosing studies continue, particularly in ischemia-reperfusion models where short-term cardiolipin stabilization shows protective effects.

What's the Difference Between SS-31 and Elamipretide?: Full Comparison

Key Takeaways

• SS-31 and elamipretide are the exact same tetrapeptide (D-Arg-Dmt-Lys-Phe-NH2) with identical molecular weight (640.77 g/mol) and CAS number (736992-21-5). The name changed when the compound advanced from academic research to clinical trials.
• The peptide binds cardiolipin in the inner mitochondrial membrane at a 1:1 molar ratio, stabilizing cristae structure and preventing cytochrome c release even under oxidative stress.
• SS-31 was the original research code from Cornell's Szeto-Schiller peptide series (early 2000s); elamipretide is the WHO-assigned International Nonproprietary Name adopted by Stealth BioTherapeutics in 2015.
• Academic literature published before 2015 predominantly uses SS-31, while clinical trial data (Phase II/III) and regulatory filings cite elamipretide. Both reference the same compound.
• Researchers conducting meta-analyses or literature reviews must recognize that SS-31 and elamipretide studies are describing one molecule at different development stages, not two separate compounds.
• The peptide's resistance to degradation comes from D-arginine at position one and dimethyltyrosine at position two. Both non-natural amino acids that prevent peptidase cleavage.
• Suppliers may list this compound under either name; always verify the CAS registry number (736992-21-5) to confirm molecular identity before procurement.

What If: SS-31 and Elamipretide Scenarios

What If I Find Studies Citing Both Names — Are They Comparable?

Yes. Studies citing SS-31 and those citing elamipretide are directly comparable because they reference the same peptide at different points in its development timeline. When conducting systematic reviews or meta-analyses of mitochondrial-targeting peptides, include both search terms ('SS-31' and 'elamipretide') to capture the full evidence base. The molecular mechanism, amino acid sequence, and cardiolipin-binding affinity remain identical across all published studies regardless of nomenclature.

What If a Supplier Lists SS-31 at a Lower Price Than Elamipretide?

Verify the CAS number (736992-21-5) and request a certificate of analysis showing purity via HPLC. Price differences between 'SS-31' and 'elamipretide' from the same supplier often reflect marketing segmentation rather than synthesis differences. If the CAS number matches and purity exceeds 98%, the peptides are functionally equivalent. Lower-priced 'SS-31' may indicate research-grade synthesis without GMP certification, which is acceptable for in vitro work but not for clinical applications.

What If I'm Designing a Mitochondrial Protection Protocol — Which Name Should I Use in My Methods Section?

Use 'elamipretide (SS-31)' in your methods section to ensure clarity across both clinical and basic science audiences. This dual nomenclature appears in recent high-impact publications (JAMA Cardiology, Genetics in Medicine) and prevents confusion when readers cross-reference older mechanistic studies that cite SS-31 exclusively. Always include the CAS number (736992-21-5) in the first mention to eliminate ambiguity.

The Blunt Truth About Mitochondrial Peptide Naming

Here's the bottom line: the pharmaceutical industry's practice of renaming research peptides during clinical development creates unnecessary confusion that fragments literature and complicates evidence synthesis. SS-31 and elamipretide are identical. Claiming they differ in any mechanistic or structural way is incorrect. The name change reflects regulatory convention, not chemistry. Researchers lose time cross-referencing studies that should be immediately recognizable as describing the same molecule. Our team has reviewed procurement inquiries where labs nearly ordered both 'SS-31' and 'elamipretide' from different suppliers, assuming they were testing two compounds, when in fact they were sourcing the same peptide twice at different price points.

The broader issue: this naming pattern repeats across peptide research. BPC-157 has no formal INN because no pharmaceutical company has pursued FDA approval. TB-500 is often conflated with thymosin beta-4, though TB-500 is technically a synthetic fragment. The lack of standardized nomenclature in peptide science makes systematic reviews harder than they should be and increases the risk of duplicate sourcing or misattributed efficacy claims. If you're working with mitochondrial-targeting peptides, verify CAS numbers in every order and cross-reference both names in every literature search. The academic-to-clinical name transition is inevitable, and recognizing it prevents wasted resources.

For researchers evaluating mitochondrial health compounds, our Energy Mitochondria Fatigue Bundle includes peptides with direct mitochondrial effects verified through small-batch synthesis and third-party HPLC analysis. Every product is labeled with its CAS number, amino acid sequence, and any alternate nomenclature to eliminate sourcing ambiguity.

The mitochondrial-targeting peptide formerly known as SS-31. Now elamipretide. Remains one of the most studied cardiolipin-binding compounds in bioenergetics research. The name changed, but the science didn't. Recognize the equivalence, cite both terms in your methods, and verify molecular identity with CAS numbers rather than relying on supplier labels alone.