MOTS-c dissolves in bacteriostatic water, and that is the standard solvent for it in research. Its four basic residues give it a strong positive charge at the pH of bacteriostatic water, so it needs no acid and no organic solvent. Its aromatic middle, Tyr-Ile-Phe-Tyr, is the part that can make it slower to clear at high concentration, so slow water and gentle swirling still matter.
Why MOTS-c dissolves
Charge does most of the work. The sequence Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg carries three arginines and a lysine plus the N-terminal amine, against one glutamic acid and the C-terminal carboxyl. From that count we calculate a net charge of about plus 3 across pH 5 to 7 and an isoelectric point near pH 10.6. These are our calculations from standard pKa values, not a measured figure. A peptide is least soluble at its isoelectric point, where its charges cancel and molecules stop repelling each other. Bacteriostatic water, specified at pH 5.7 within a 4.5 to 7.0 range, sits far below that point, so dissolved MOTS-c molecules carry a like charge and repel one another.
The counterweight is its hydrophobic content. Of 16 residues, eight have hydrophobic or aromatic side chains: two methionines, a tryptophan, two tyrosines, an isoleucine, a phenylalanine and a leucine. Four of them sit together at positions 8 to 11. That is why one of our guides describes MOTS-c as a short, comparatively hydrophobic sequence with known handling considerations (why peptides gel or go cloudy). In practice the charge wins: one chemical supplier’s instructions are simply to make the stock solution by dissolving the solid in water (Cayman Chemical, item 29785), and our storage page quotes another supplier’s solubility figure for water.
Bacteriostatic water first
Bacteriostatic water is sterile water with 0.9% benzyl alcohol, which allows a refrigerated vial to be accessed more than once. For MOTS-c it is the solvent of choice: the peptide dissolves fully in it, and the preservative supports repeated access over the 8 to 12 week fridge window described on how long MOTS-c lasts. Sterile water works for a vial that will be accessed once. The difference is explained in bacteriostatic water explained.
Why not acetic acid?
Laboratories sometimes add a little dilute acetic acid to coax basic or hydrophobic peptides into solution, because lowering the pH adds positive charge. MOTS-c is already strongly positive in plain bacteriostatic water, so acid adds very little, and it adds a variable the standard preparation on our storage and reconstitution pages does not include. Acid does not protect the methionines either: oxidation is driven by oxygen, light and trace metals rather than by pH. Plain bacteriostatic water is simpler and sufficient.
Saline and sodium chloride
MOTS-c also dissolves in 0.9% sodium chloride. Salt ions screen the charges on a peptide, which can weaken the repulsion that keeps molecules apart, and for a peptide with an aromatic run that can make association slightly easier at high concentration. At normal saline strength and research concentrations, far below the isoelectric point, this is not a practical concern. This is general peptide chemistry rather than a MOTS-c specific measurement. For a multi-access vial, bacteriostatic water remains the choice because of its preservative.
Concentrations that dissolve cleanly
A 10 mg vial is commonly mixed with 1 to 5 mL of bacteriostatic water: 2 mL gives 5 mg/mL and 1 mL gives 10 mg/mL. The 40 mg vial gives 20 mg/mL with 2 mL, 10 mg/mL with 4 mL and 5 mg/mL with 8 mL. Those are the figures our MOTS-c reconstitution page uses for its tables. They dissolve to a clear, colourless solution with gentle swirling.
The 40 mg vial deserves a moment’s thought. At 20 mg/mL, molecules with an aromatic run meet each other far more often, so a slightly larger volume gives a little more margin if a vial is slow to clear. A larger water volume does not change the amount of peptide; it spreads it more thinly. Whatever volume is chosen, write the concentration on the vial.
Cloudiness and gelling: what causes them
- Water jetted onto the cake. A strong stream traps air and creates foam, which looks cloudy and also dissolves more oxygen into the solution. Running the water down the inside wall of the vial avoids both.
- Shaking. Agitation creates air and liquid interfaces where peptides can unfold and clump, and it works oxygen into a solution whose methionines oxidise. Swirl or roll instead.
- Cold water onto cold powder. Both at fridge temperature slows dissolving. Letting the vial and the water reach room temperature first helps.
- Haze appearing later in storage. This suggests the vial was kept too warm, frozen and thawed, or contaminated, and the solution is discarded.
Brief cloudiness that clears within 10 to 15 minutes of mixing is normal and usually trapped air. The mixing method step by step is in how to reconstitute peptides with bacteriostatic water.
Related MOTS-c pages
How the dissolved peptide behaves over time is on the MOTS-c stability page, and bench technique is on the MOTS-c handling page.
All products supplied by Vistara Labs are intended for laboratory research use only. They are not drugs, are not approved for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any condition. Nothing on this page constitutes medical advice or guidance for use in humans.
