Follistatin-315
Also known as: FS-315, FST-315
Molecular Identifiers
Molecular Weight
~35 kDa
Overview
315-amino acid isoform of follistatin with preferential selectivity for myostatin over activin. Considered more specific for muscle growth with less impact on the reproductive and endocrine axes.
Clinical interest in Follistatin-315 centers on preferential myostatin inhibition, with lower activin affinity compared to Follistatin-344. The practical goal is to promote muscle hypertrophy and reduce fibrosis with less interference on the reproductive hormonal axis and FSH levels. Human evidence is scarce and based mostly on preclinical work and small series.
There is no regulatory approval for Follistatin-315 by any agency. It is marketed as a recombinant research protein and, in some markets, dispensed by compounding pharmacies as off-label use in mass-gain protocols, in short subcutaneous cycles of 10–30 days due to its high cost and short half-life. Myostatin inhibitors are prohibited by WADA at all times (in and out of competition).
In direct comparison with Follistatin-344, the 315 isoform is shorter and has a predominantly plasma/systemic profile, with reduced affinity for cell-surface heparan sulfate. In practice this translates into action more focused on myostatin, with less inhibition of activins and less impact on FSH and the reproductive axis than the 344 form — useful when the goal is hypertrophy while preserving gonadal signaling as much as possible. Both forms, however, share regulatory status (no approval) and WADA classification.
GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEW Protein of 315 amino acids. Shorter isoform of Follistatin-344.
Half-life
~1.5-2 hours
Administration Route
Subcutaneous
Category
Specialized Research
Mechanism of Action
- Selective myostatin inhibition
- Lower affinity for activin compared to FS-344
- Promotion of muscle hypertrophy
- Less interference with the reproductive hormonal axis
Dosage Protocol
Data compiled from the literature. This does not constitute medical advice.
| Parameter | Value |
|---|---|
| Dose | 100-200 mcg per injection |
| Frequency | Once daily |
| Timing | Morning or post-workout |
| Duration | 10-30 days |
Reported Side Effects
Adverse effects described in the literature. Severity and frequency vary between individuals.
- Injection site redness
- Fatigue
- Headache
Product Properties
| Purity | >97% |
| Appearance | White lyophilized powder |
| Solubility | Soluble in water and bacteriostatic water. Reconstitute gently — do not vortex. |
| Source | Recombinant DNA technology (E. coli or HEK293 cells) |
| Storage | Lyophilized: -20°C for up to 2 years, 2-8°C for up to 6 months. Reconstituted: 2-8°C for up to 2 weeks. Protect from light and moisture. Avoid repeated freeze-thaw cycles. Aliquot for long-term storage. |
Presentations & Preparation
Vials of Follistatin-315 found in the research market:
Reconstitution
- Diluent: Bacteriostatic water
- Volume: 1 ml per 1 mg vial
- Inject diluent slowly
- Gently swirl
- Immediate use recommended
Storage
- Lyophilized: Frozen -20°C (long-term)
- Reconstituted: Refrigerated 2-8°C (up to 7 days)
- Avoid freeze/thaw cycles
- Protect from light
Scientific Studies
Published studies on Follistatin-315.
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