MOTS-c — mitochondrial open reading frame of the 12S rRNA-c — is a 16-residue peptide with the sequence MRWQEMGYIFYPRKLR. What distinguishes it from most peptides in this catalog is where its coding sequence lives: not in the nuclear genome, but inside the mitochondrial 12S ribosomal RNA gene, in a short open reading frame (sORF) reported in 2015 by a group looking for additional mtDNA-encoded signaling peptides after the precedent set by humanin [1]. It is therefore classed as a mitochondria-derived peptide (MDP), a small family that at the time of the most recent review comprised eight described members: humanin, MOTS-c, and the six small humanin-like peptides [12].

Two features of the sequence matter for anyone handling the synthetic material. It contains two methionine residues (positions 1 and 6) and a single tryptophan (position 3) — three side chains that are among the more oxidation-labile in peptide chemistry. It also carries three basic residues in the C-terminal quarter (R13, K14, R16), and position 14 is exactly where a naturally occurring human sequence variant falls.

The category itself is worth a sentence, because it is the reason MOTS-c attracts attention out of proportion to the size of its literature. Mitochondrial DNA was long annotated as encoding 13 proteins, all of them respiratory chain subunits. The MDP class holds that the same circular genome also carries short open reading frames encoding microproteins that modify cell metabolism, and the search that produced MOTS-c was explicitly motivated by the earlier identification of humanin — one sORF suggesting the existence of others [1, 12]. Whether MOTS-c and its relatives are the leading edge of a larger coding layer or a handful of special cases is, at present, an open question rather than a settled one.

Identity and characterization

The identity data on this page come from the site's verified compound map and match the figures displayed on the MOTS-c product listing:

The two sulfur atoms in the formula are the two methionine thioethers; a formula for this sequence carrying more or fewer than two is a formula for something else. That check is worth performing on any supplier's specification sheet, because a molecular formula that does not reconcile with the stated sequence is the cheapest possible signal that a document has been copied rather than measured.

Mechanism as studied

The original characterization placed MOTS-c upstream of AMP-activated protein kinase (AMPK), but by an indirect route. The peptide's cellular actions inhibited the folate cycle and the de novo purine biosynthesis pathway tethered to it; the resulting accumulation of the pathway intermediate AICAR was proposed as the proximate AMPK activator, with skeletal muscle identified as the apparent primary target tissue [1]. This is a metabolite-mediated mechanism, not receptor occupancy, and it is worth stating plainly that no cell-surface receptor for MOTS-c has been established in the literature reviewed here. The distinction matters for how the compound behaves in an assay: a peptide that acts by perturbing a one-carbon metabolic pathway should show readouts that depend on the folate and purine status of the medium, and should be sensitive to whether AMPK is intact in the cells used. Those expectations follow from the mechanism as described [1]; they are an inference about experimental design, not a result someone has published.

A second line of work moved the peptide inside the nucleus. Under glucose restriction and other metabolic stress, MOTS-c was shown to translocate from the cytoplasm to the nucleus in an AMPK-dependent manner, where it associated with stress-responsive transcription factors including NFE2L2/NRF2 and where the genes whose expression changed were enriched for antioxidant response elements (AREs) [2]. The authors framed this as evidence for mitochondrial-to-nuclear regulatory traffic — a mitochondrially encoded factor acting on nuclear gene expression — rather than as a demonstrated pathway from peptide to a physiological endpoint.

The clearest direct binding result to date is protein kinase CK2. In cell-free systems, MOTS-c bound CK2 directly and increased its activity; in mice, effects on skeletal muscle glucose uptake and on muscle mass were blunted when CK2 activity was suppressed, and the peptide's action proved tissue-dependent — CK2 activity rose in muscle and fell in adipose tissue, which the authors ascribed to MOTS-c differentially modifying CK2-interacting proteins in the two tissues [3].. The same study reported that a naturally occurring sequence variant binds CK2 more weakly and does not activate it, which is the most direct structure-activity evidence available for this peptide.

A 2025 study added a candidate transport mechanism for the nuclear step. In rat lung ischemia–reperfusion and in endothelial cells subjected to hypoxia–reoxygenation, reactive-oxygen-species-dependent phosphorylation of the motor protein MYH9 at Ser1943 by the CK2 alpha subunit preceded MOTS-c binding to MYH9–γ-actin complexes, and RNA-seq with ChIP-seq implicated ARE-bearing genes including HMOX1 and NQO1 [9]. Read alongside the 2018 nuclear translocation work [2], it offers a physical route for a step that had been described phenomenologically; it is a single study in one model system and should be treated as such.

Model systems in which it has actually been examined

Most of the mechanistic work is rodent and cell culture. Mouse studies have used systemically administered synthetic peptide and reported changes in physical performance across young, middle-aged and old animals, in nuclear gene expression, in skeletal muscle metabolism, and in myoblast adaptation to metabolic stress [4]. Rat work covers the lung ischemia–reperfusion model described above [9]. Cell-free assays established the CK2 interaction [3]. Cultured cells appear in two distinct roles: as the system in which the folate-cycle and AMPK readouts were first obtained [1], and as the system in which nuclear translocation under glucose restriction was observed [2].

Endogenous MOTS-c has also been tracked as an exercise-responsive protein rather than as an administered agent. In rodents, four to eight weeks of voluntary running raised intramuscular MOTS-c protein roughly 1.5- to 5-fold across plantaris, medial gastrocnemius and tibialis anterior, alongside increased mtDNA, with the elevation persisting through four to six weeks of detraining [7]. In humans, exercise was reported to induce MOTS-c expression in skeletal muscle and in circulation [4]. Note how uneven the subcellular data are in the same rodent study: nuclear translocation after a downhill running challenge was detected in two of six mouse soleus muscles and in none of the plantaris muscles from the same animals [7]. That is the kind of result that gets flattened into "exercise drives MOTS-c into the nucleus" and should not be.

The human evidence is genetic and observational. An East Asian-specific mitochondrial variant, m.1382A>C (rs111033358), changes residue 14 from lysine to glutamine, producing the K14Q form of the peptide. Carriers of the C allele showed a higher proportion of MHC-IIx myosin heavy chain — an index of fast-twitch fiber — in 211 Japanese individuals, and the C allele was more frequent among sprint and power athletes (6.5%) than controls (5.1%) or endurance athletes (2.9%) [5]. In a separate cohort analysis, the K14Q peptide showed reduced insulin-sensitizing activity in vitro relative to the wild-type sequence, and the associated phenotypes differed by sex and by physical activity level [6]. An earlier commentary had raised the same polymorphism as a possible contributor to longevity in a Japanese population, but stated explicitly that this was a suggestion requiring more research [11] — and it is worth keeping the hedge attached, because it is frequently dropped.

What the evidence does not establish

No receptor. The binding partner with the strongest direct evidence is an intracellular kinase, CK2 [3]; the original mechanism was metabolite-mediated via the folate cycle [1]. Nothing in this literature identifies a cell-surface receptor, and descriptions of MOTS-c as a "mitokine" acting on a receptor are ahead of the data.

Not universally active. In cybrid cells carrying the m.3243A>G mtDNA mutation, exogenous synthetic MOTS-c produced no significant change in ATP content, in mRNA or protein levels of mitochondrial complex subunits, or in basal and stimulated respiration; transfecting the cells to express MOTS-c endogenously produced the same null result [8]. The authors' own reading was that, in contrast to other mitochondria-derived peptides, MOTS-c does not improve mitochondrial dysfunction in that system. A compound described as improving mitochondrial function has a directly published negative result in one mitochondrial-dysfunction model, and that belongs in any honest summary.

Measurement is not settled. Circulating MOTS-c is generally quantified by antibody-based assays. One randomized human study that measured serum MOTS-c with a named commercial competitive ELISA found no significant change across 24 weeks of treatment; its authors suggested that the study drug's inability to target skeletal muscle — which they describe as the major tissue for MOTS-c production and secretion — might have limited its regulatory effects on circulating MOTS-c, and they wrote that further studies are needed [10]. Two cautions follow from that as inference, not as their conclusion: quantitative comparisons across studies that used different immunoassays are weak evidence, and a plasma concentration is not a muscle concentration.

"Exercise mimetic" is a label, not a finding. The term is used in the primary literature for MOTS-c [5], and it rests on two separable observations: that endogenous muscle and circulating MOTS-c rise with training [4, 7], and that administered peptide improved physical performance in mice [4, 7]. Neither establishes that the peptide reproduces the transcriptional, vascular and mechanical consequences of exercise, and the papers themselves do not claim it does. Treating the shorthand as the result is the most common way this literature gets misreported.

No study in this set administered MOTS-c to human subjects. The human data cited here are observational: genotype–phenotype association [3, 5, 6], measurement of endogenous or circulating peptide [4, 9, 10], and review or commentary [11, 12]. Claims about outcomes in people are not supported by any of it, and this page makes none.

Finally, a disclosure that any reader of this literature should know: Finally, a disclosure that any reader of this literature should know: several of the foundational papers carry competing-interest statements noting that intellectual property covering MOTS-c was licensed by UCLA to a commercial developer and that a senior author is an advisor to and stockholder in it [3, 12]. That does not invalidate the work — the results are published, peer-reviewed and in several cases independently extended — but it explains why the field's framing has been consistently optimistic and why independent replication carries extra weight here.

Handling and stability

Searches of the indexed literature returned no study characterizing the lyophilizate stability, reconstituted shelf life, freeze–thaw tolerance or solution degradation profile of MOTS-c specifically. That absence is the honest answer, and it means the handling guidance below is general peptide practice and chemical inference from the sequence, not a finding transcribed from a paper.

  • The material is supplied as a lyophilized powder and stored refrigerated at 2–8 °C, consistent with the product listing.
  • Two methionines and one tryptophan make oxidation the most plausible degradation route for this sequence. Minimizing headspace oxygen, light exposure and repeated warming of the sealed vial follows from that chemistry — it is not a claim that oxidation has been measured for this peptide.
  • A 16-residue sequence at 2174.6 g/mol is small enough that identity is straightforwardly confirmable by mass spectrometry, and an oxidized methionine shifts the observed mass by a readily recognizable +16 Da per residue. Where a study's conclusion turns on the peptide being intact, that is a check worth running rather than assuming.
  • Any laboratory relying on this compound for quantitative work should verify identity and purity in-house rather than inferring it from a certificate. Certificates published on this site state the vial size and, where applicable, the batch they were issued against; treat a certificate whose batch reads "Unknown" as evidence about a sample, not about your sample.

Open questions

Where the peptide is translated, how much of it a cell actually makes, and how that pool is regulated remain measured indirectly through antibody-based detection [7, 10] rather than by direct quantification. Whether the nuclear pool and the cytoplasmic pool represent distinct signaling roles is suggested by the translocation work [2, 9] but not resolved. The CK2 result [3] sharpens the mechanism considerably, yet leaves open how a peptide with no identified surface receptor reaches an intracellular kinase after systemic administration — a transport question that the MYH9 work addresses for the nucleus but not for the plasma membrane. And the K14Q variant [5, 6] offers a natural experiment that the field has so far used mostly for association studies; the structural basis of its weaker CK2 binding is the kind of question that would move this from a phenomenology to a mechanism.