What is SS-31?
SS-31 is a short synthetic peptide classified within the Szeto-Schiller (SS) family of aromatic-cationic peptides. It is composed of four amino acid residues arranged in the sequence D-Arg-Dmt-Lys-Phe-NH2, where Dmt denotes 2',6'-dimethyl-L-tyrosine and the carboxy terminus is capped as a primary amide (NH2). The molecule carries the CAS registry number 736992-21-5, the molecular formula C32H49N9O5, and a molecular weight of 639.80 g/mol.
Structurally, SS-31 is notable for its alternating pattern of aromatic and basic residues, which gives the peptide a net positive charge under physiological pH while retaining a degree of hydrophobicity. The inclusion of a D-configuration arginine and the non-standard, dimethylated tyrosine residue (Dmt) distinguishes it from peptides built exclusively from canonical L-amino acids, and these modifications are associated with the material's resistance to common aminopeptidase activity in laboratory preparations. The primary amide C-terminus further differentiates it from a free-acid peptide of the same sequence.
In the scientific literature, SS-31 is studied as a mitochondria-associated aromatic-cationic peptide and is frequently examined in in-vitro models of mitochondrial membrane biology, including research characterizing its interaction with the phospholipid cardiolipin of the inner mitochondrial membrane. It is referenced in these contexts strictly as a research reagent. This monograph describes the identity, chemistry, and handling of the material only and makes no representation regarding physiological activity, therapeutic use, or outcomes of any kind. SS-31 is intended for laboratory research use only and is not a drug, food, or cosmetic.
Reconstitution & handling
SS-31 is typically supplied as a lyophilized (freeze-dried) solid. For reconstitution in a research setting, bacteriostatic or sterile water is the most common vehicle owing to the peptide's cationic, hydrophilic character; the multiple basic residues (D-Arg, Lys) confer good aqueous solubility across a broad concentration range. The solvent should be introduced slowly down the wall of the vial and allowed to dissolve by gentle swirling rather than vigorous agitation or vortexing, which can promote foaming and shear at the air-liquid interface. The peptide should be permitted to go fully into solution before the resulting stock is aliquoted.
Because the amide-capped tetrapeptide is relatively small and well solvated in water, it generally dissolves readily to a clear, colorless solution; persistent cloudiness may indicate incomplete dissolution or contamination and warrants inspection. Where a buffered milieu is required for a given assay, mildly acidic to neutral aqueous buffers are generally compatible, and any co-solvent selection should be validated for the specific downstream application. All reconstitution should be performed under clean technique using appropriate personal protective equipment.
Storage & stability
In its lyophilized form, SS-31 is best stored sealed and protected from light and moisture at -20 C, conditions under which the dry peptide is stable for extended periods. Once reconstituted, the solution should be kept refrigerated at 2-8 C for near-term use or divided into single-use aliquots and frozen at -20 C or below to limit degradation; repeated freeze-thaw cycles should be avoided, as they can compromise peptide integrity. Allowing vials to equilibrate to room temperature before opening helps minimize condensation and moisture uptake by the hygroscopic solid. Actual working stability should be confirmed empirically for the specific buffer, concentration, and storage format used in a given laboratory.
How it's tested
Identity and purity of SS-31 are verified analytically prior to release. Purity is assessed by reversed-phase high-performance liquid chromatography (HPLC), with material specified at greater than or equal to 99% purity. Identity and molecular weight are confirmed by mass spectrometry (MS), which resolves the intact peptide against the expected average mass corresponding to the formula C32H49N9O5 (MW 639.80) and the D-Arg-Dmt-Lys-Phe-NH2 sequence. A Certificate of Analysis (COA) documenting these results is available for each lot, providing traceable, verifiable confirmation of composition and purity.