Long amber peptide chain beside a compact tetrapeptide sphere cluster in front of a mitochondrial membrane fold, comparing MOTS-c and SS-31 structures.
Mindful Research

MOTS-c vs SS-31: Two Mitochondria-Directed Peptides Compared

By: Mindful Research Team3 min read

Key takeaways

  • MOTS-c is a 16-residue mitochondrial-genome-encoded peptide; SS-31 is a synthetic aromatic-cationic tetrapeptide.
  • MOTS-c is studied for folate-cycle, AICAR and AMPK signaling; SS-31 for inner-membrane and cardiolipin association.
  • At 2174.6 versus 639.8 g/mol, equal mg/mL is very different molarity, so compare on a molar basis.
  • Share respiration and ATP readouts across arms and keep pathway-specific readouts separate.
  • For in vitro research use only.

MOTS-c and SS-31 are both used in mitochondrial research but differ in kind: MOTS-c is a 16-residue peptide encoded in the mitochondrial genome and studied for folate-cycle and AMPK signaling, while SS-31 is a synthetic four-residue peptide studied for its association with the inner mitochondrial membrane. This comparison covers structure, reported mechanism and assay design for MOTS-c and SS-31 as laboratory materials.

How do MOTS-c and SS-31 compare side by side?

Property MOTS-c SS-31 (elamipretide)
Origin Encoded by the mitochondrial 12S rRNA gene Synthetic, designed aromatic-cationic tetrapeptide
Length 16 amino acids 4 amino acids
Sequence MRWQEMGYIFYPRKLR D-Arg-Dmt-Lys-Phe-NH2
Molecular formula C101H152N28O22S2 C32H49N9O5
Molecular weight 2174.6 g/mol 639.8 g/mol
CAS number 1627580-64-6 736992-21-5
Reported site of activity Cell signaling (folate cycle, AMPK; reported nuclear translocation under stress) Inner mitochondrial membrane, associated with cardiolipin
Typical in vitro readouts Phospho-AMPK, AICAR, ATP and AMP ratios, respiration Membrane potential, mitochondrial reactive oxygen species, cardiolipin status, respiration
Vial sizes listed 10 mg and 40 mg 10 mg and 50 mg

How do their structures differ?

SS-31 is a short, positively charged tetrapeptide built on an alternating aromatic and cationic residue pattern, including D-arginine and dimethyltyrosine. MOTS-c is a longer peptide with a natural sequence, two methionines and several basic residues. The size difference matters in practice: at 639.8 g/mol, 1 mg/mL of SS-31 is about 1.56 mM, versus about 0.46 mM for MOTS-c, so equal mass concentrations are very different molar concentrations. Use molarity when comparing the two.

How do their reported mechanisms differ?

MOTS-c has been reported to act on cellular metabolic signaling, through the folate cycle, AICAR and AMPK; the readouts are described in AMPK and folate-cycle assays for MOTS-c in vitro. SS-31 is reported to associate with cardiolipin on the inner mitochondrial membrane, which is the focus of SS-31 and the inner mitochondrial membrane. These are literature descriptions, not outcome claims, and each should be tested in your own cell system.

How would you design an experiment that uses both?

  • Parallel arms: run each peptide in its own arm, matched on molar concentration, vehicle and incubation time.
  • Shared readouts: respiration by extracellular flux and ATP levels allow direct comparison across both arms.
  • Distinct readouts: keep phospho-AMPK and AICAR for MOTS-c, and membrane potential and mitochondrial reactive oxygen species probes for SS-31.
  • Controls: a scrambled MOTS-c-length peptide and a matched-charge tetrapeptide control keep the two arms interpretable.

Verify the identity of each material before comparing them; see the COA guides for MOTS-c and SS-31.

Related research guides

Research-use note

All materials discussed are supplied for in vitro laboratory research use only, and are not for human or animal use.

Frequently asked questions

What is the difference between MOTS-c and SS-31?

MOTS-c is a 16-residue peptide encoded in the mitochondrial genome and studied for folate-cycle and AMPK signaling, while SS-31 is a synthetic four-residue peptide studied for its association with the inner mitochondrial membrane. View MOTS-c

How do their molecular weights compare?

MOTS-c is 2174.6 g/mol and SS-31 is 639.8 g/mol, so 1 mg/mL is about 0.46 mM for MOTS-c and about 1.56 mM for SS-31. View SS-31

Which readouts are shared and which are specific?

Respiration by extracellular flux and ATP levels can be shared; phospho-AMPK and AICAR are specific to MOTS-c, while membrane potential and mitochondrial reactive oxygen species probes suit SS-31. AMPK and folate-cycle assays

How should the two be compared in one experiment?

Run parallel arms matched on molar concentration, vehicle and incubation time, with a scrambled or matched-charge peptide control for each.

Is it for human or animal use?

No. Both are supplied for in vitro laboratory research use only.

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