A MOTS-c 10 mg vial contains about 4.60 micromoles of peptide (10 mg divided by 2174.6 g/mol), so the stock concentration is set entirely by the solvent volume you add: 10 mg in 1 mL gives 10 mg/mL, or about 4.60 mM. This guide works through the concentration arithmetic for MOTS-c for in vitro assay preparation. Happy Peptides lists 10 mg and 40 mg vials, and a 5 mg column is included for reference.
How do you convert mg per mL to molarity?
Molarity (mol/L) equals mass concentration (g/L) divided by molecular weight (g/mol). With a molecular weight of 2174.6 g/mol, 1 mg/mL equals 1 g/L, which is 0.46 mM. Likewise 1 mg of peptide is 0.46 micromoles.
What stock concentrations result from common solvent volumes?
| Solvent volume | 5 mg (mM) | 10 mg (mg/mL) | 10 mg (mM) | 40 mg (mg/mL) | 40 mg (mM) |
|---|---|---|---|---|---|
| 1 mL | 2.30 | 10.0 | 4.60 | 40.0 | 18.39 |
| 2 mL | 1.15 | 5.0 | 2.30 | 20.0 | 9.20 |
| 4 mL | 0.57 | 2.5 | 1.15 | 10.0 | 4.60 |
| 5 mL | 0.46 | 2.0 | 0.92 | 8.0 | 3.68 |
| 10 mL | 0.23 | 1.0 | 0.46 | 4.0 | 1.84 |
The 5 mg column applies to any 5 mg vial (the "mots c 5mg" format). Very concentrated stocks, such as 40 mg in 1 mL, may exceed solubility, so choose a volume consistent with the solubility guidance on the certificate of analysis.
How do you dilute a stock to assay working concentrations?
Use C1 x V1 = C2 x V2. For example, about 217 microliters of a 4.60 mM stock (10 mg in 1 mL) plus 783 microliters of diluent gives 1 mL of a 1 mM intermediate. That intermediate diluted 1:100 in assay buffer gives 10 micromolar, and a half-log series (10, 3.16, 1, 0.316 and 0.1 micromolar) covers a typical concentration-response curve. Keep final solvent content constant across all wells, including the vehicle control. The general method is explained in stock and working solutions: serial dilution for in-vitro assays.
What affects the accuracy of the math?
- Net peptide content: lyophilized powder includes counter-ions and residual water, so the true peptide mass can be below the label value. Use the content figure from the certificate of analysis where it is provided.
- Solvent choice: a suitable aqueous solvent such as Reconstitution Solution is a common choice for aqueous stocks; follow the solvent's own documentation.
- Methionine oxidation: MOTS-c has two methionine residues that can oxidize in solution; prepare single-use aliquots to limit storage in solution and repeated freeze-thaw cycles.
To confirm the material itself before doing the math, see MOTS-c COA and purity; for the assays these stocks feed, see the AMPK and folate-cycle assay guide.
Related research guides
- MOTS-c quick-reference profile: sequence, origin and assays
- Molar concentration: a worked example for peptides
- Concentration calculator: mg/mL and molarity explained
Research-use note
All materials discussed are supplied for in vitro laboratory research use only, and are not for human or animal use.
