SS-31 Peptide in Canada: Cardiolipin and Mitochondrial Targeting
Most research peptides are defined by a receptor. SS-31 is defined by a lipid. Labs sourcing SS-31 peptide in Canada, also catalogued under the name elamipretide, are buying a four-residue molecule whose studied activity comes from where it settles inside the cell, namely the inner mitochondrial membrane, and from its association with cardiolipin there. That has knock-on effects for assay choice, for labware, and for what the certificate on a multi-vial order needs to show. This article covers the structure, the targeting chemistry, the cardiolipin partnership and the practical checks a QC team should make.
SS-31 peptide in Canada: the molecule on the certificate
SS-31 belongs to the Szeto-Schiller family of short peptides built on an alternating pattern of aromatic and positively charged residues. Its sequence is D-Arg-Dmt-Lys-Phe-NH2, where Dmt is 2′,6′-dimethyltyrosine. The molecular formula is C32H49N9O5 and the average mass is close to 639.8 g/mol.
| Position | Residue | Why it matters |
|---|---|---|
| 1 | D-arginine | Positive charge; the D-configuration resists proteases and cannot be confirmed by mass alone |
| 2 | 2′,6′-dimethyltyrosine | Aromatic, non-standard residue; gives the molecule useful absorbance near 280 nm |
| 3 | L-lysine | Second positive side chain |
| 4 | L-phenylalanine, amidated | Aromatic; the C-terminal amide removes a negative charge |
With two basic side chains plus the free N-terminus, and no acidic groups, the peptide carries a net charge of about +3 at neutral pH. That charge, paired with two aromatic rings, drives both its biology and most of its handling problems.
How the peptide reaches the inner membrane
Classic mitochondrial probes, such as triphenylphosphonium (TPP) conjugates, are lipophilic cations pulled into the matrix by the negative-inside potential across the inner membrane. The catch is obvious once stated: when mitochondria depolarise, those probes stop accumulating, so they concentrate least in the organelles an experimenter may most want to study.
The SS peptides are reported to behave differently. Published work describes their uptake as largely independent of membrane potential, with the peptide associating with the inner membrane rather than being driven electrically into the matrix. That is a claim a lab can test directly instead of citing. Treat cells with an uncoupler such as FCCP and compare localisation of SS-31 against a TPP-based comparator. If the reported mechanism holds, SS-31 localisation should persist while the TPP signal drops.
Cardiolipin, the lipid partner
Cardiolipin is an unusual phospholipid: two phosphatidyl groups joined through a central glycerol, giving four fatty acyl tails beneath a compact head group. Its cone-like shape favours tight negative curvature, which suits the folded cristae of the inner membrane where it is concentrated.
The literature proposes that SS-31 binds cardiolipin and, through that interaction, influences two structural features:
- Respiratory supercomplexes. Complexes I, III and IV assemble into larger units with cardiolipin at their interfaces. When cardiolipin is oxidised or depleted, those assemblies loosen, electron transfer becomes less efficient and more electrons escape to oxygen.
- Cytochrome c peroxidase activity. Bound to cardiolipin, cytochrome c can act as a peroxidase and oxidise the very lipid anchoring it. Oxidised cardiolipin loosens its hold, and cytochrome c release is an early step in intrinsic apoptosis in cell models.
The mechanistic point is that stabilising cardiolipin would act before reactive oxygen species form, not by mopping them up afterwards. A good experiment is designed to tell those two possibilities apart.
Readouts and controls when there is no receptor
Without a receptor there is no binding constant or selectivity ratio to report, so everything rests on functional mitochondrial measurements and on well-chosen controls. Common readouts include:
- Oxygen consumption by extracellular flux or high-resolution respirometry, normalised to cell number.
- Membrane potential with TMRM or JC-1, always alongside an uncoupler control.
- Mitochondrial superoxide with MitoSOX, remembering that the dye’s own uptake depends on potential.
- Supercomplex assembly by blue-native PAGE, the readout closest to the proposed mechanism.
- Cristae structure by electron microscopy, and cardiolipin oxidation by lipidomics where justified.
Controls matter as much as readouts. A general antioxidant separates cardiolipin-specific effects from simple redox buffering. A charge-matched scrambled peptide accounts for non-specific effects of any cationic peptide on membranes. Normalising to citrate synthase activity or mitochondrial DNA copy number prevents a change in mitochondrial quantity being read as a change in function.
Concentration also needs care. Membrane-active compounds often give bell-shaped concentration-response curves, with an effect at low concentrations that fades or reverses as the membrane itself is disturbed. Running a full range in your own system is more reliable than borrowing a single concentration from a paper.
Losing peptide to the tube wall
A small, strongly cationic peptide sticks to surfaces. At the nanomolar concentrations typical of cell work, a noticeable share of SS-31 can bind to glass or ordinary polypropylene and simply leave the solution. This is one of the likeliest reasons two labs report different potencies for the same material.
- Use low-binding tubes and pipette tips for every step of a dilution series.
- Add a carrier protein to dilution buffers where the assay allows it.
- Make working dilutions fresh on the day instead of storing dilute stocks.
- Keep labware identical between vehicle and treatment arms.
What to confirm on the certificate and at receiving
For a tetrapeptide, the analytical checks are quick, but a few are easy to overlook:
- Mass. The target is unambiguous at about 639.8 g/mol for the amidated form. A mass about one dalton higher suggests the free acid rather than the amide.
- Stereochemistry. D- and L-arginine forms have identical masses. Only chiral analysis or a documented synthetic route establishes the D-residue, and most certificates do not address it.
- Detection wavelength. The aromatic residues absorb well near 280 nm, but impurities lacking those rings will be under-counted there. A purity figure at around 214 nm gives a more complete picture.
- Net peptide content and counter-ion. With three positive charges on a small molecule, counter-ions make up a larger share of the powder than for a long peptide. Residual trifluoroacetate can also interfere with sensitive cell viability and mitochondrial readouts.
At receiving, match each vial’s cap and crimp colour to the certificate you are filing, record lot and arrival condition, and move the lyophilised stock to cold, dark storage the same day. For long projects, drawing every vial from one lot keeps the adsorption and potency work comparable from start to finish.
SS-31 10 mg is stocked alongside MOTS-c, a mitochondrially encoded peptide that is often grouped with it but works through an unrelated mechanism. Both are third-party tested for purity by HPLC, certificates are published for some products, and with mix-and-match volume pricing every vial in the cart counts toward the volume break.
SS-31 and the other compounds mentioned are sold for in-vitro laboratory research only. They are not for human or veterinary use, and nothing here is guidance on any such use.
