Selank Molecular Weight, Sequence & CAS Reference
Selank is a synthetic heptapeptide derivative of the naturally occurring immunomodulatory peptide tuftsin, engineered with a C-terminal Pro-Gly-Pro sequence extension. This reference page provides verified chemical specifications, including the exact selank molecular weight sequence parameters, CAS identification, counterion dynamics, and analytical methodologies for laboratory research context.
Quick answer
Selank is a synthetic heptapeptide derivative of the naturally occurring immunomodulatory peptide tuftsin, engineered with a C-terminal Pro-Gly-Pro sequence extension. This reference page provides verified chemical specifications, including the exact selank molecular weight sequence parameters, CAS identification, counterion dynamics, and analytical methodologies for laboratory research context.
Key takeaways
- [Selank](/research-peptides/selank) is a synthetic analog of the endogenous tetrapeptide tuftsin (Thr-Lys-Pro-Arg), modified through the strategic attachment of a tripeptide sequence (Pro-Gly-Pro) at its C-terminus.
- The primary amino acid sequence of [Selank](/research-peptides/selank) is Thr-Lys-Pro-Arg-Pro-Gly-Pro, frequently abbreviated in single-letter code as TKPRPGP.
- The primary chemical parameters defining [Selank](/research-peptides/selank) free base are as follows: chemical formula $C_{33}H_{57}N_{11}O_9$, exact monoisotopic mass of 751.4341 Da, and an average molecular mass of approximately 751.88 g/mol.
- Solid-phase peptide synthesis (SPPS) yields peptides as salts due to purification protocols utilizing acidic mobile phases.
Introduction to Selank Structural Derivation and Chemical Profile
Selank is a synthetic analog of the endogenous tetrapeptide tuftsin (Thr-Lys-Pro-Arg), modified through the strategic attachment of a tripeptide sequence (Pro-Gly-Pro) at its C-terminus. Developed originally at the Institute of Molecular Genetics of the Russian Academy of Sciences, this modern heptapeptide was synthesized to enhance metabolic stability against peripheral peptidases while retaining molecular target selectivity. For investigators evaluating synthetic peptides across our all-peptides catalog, understanding the primary sequence, molecular mass, and salt formulation is essential for accurate molar calculations and in vitro assay design.
Unlike native tuftsin, which undergoes rapid enzymatic cleavage in biological matrices, the C-terminal Pro-Gly-Pro domain confers structural rigidity and resistance to carboxypeptidases. This design allows researchers to evaluate sustained biochemical interactions in cell culture models and tissue lysates. As a pure research compound, Selank is synthesized exclusively for laboratory evaluation, serving as a model molecule for studying neuro-immunological pathways, peptide degradation kinetics, and receptor binding affinities without human application.
Selank Amino Acid Sequence and Primary Structure Dynamics
The primary amino acid sequence of Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, frequently abbreviated in single-letter code as TKPRPGP. Synthesized from L-configuration amino acid residues, the N-terminal residue is L-threonine, while the C-terminus terminates with L-proline featuring a free carboxyl group (-OH) unless specifically amidated for specialized investigational setups.
The inclusion of three proline residues within a seven-amino-acid chain imparts distinct conformational properties to the peptide backbone. Proline's cyclic side chain restricts the phi ($\phi$) dihedral angles, resulting in a relatively rigid secondary structure in aqueous solution. The basic residues L-lysine (position 2) and L-arginine (position 4) contribute positive electrostatic charges at physiological pH, directly influencing the peptide's overall pI (isoelectric point) and its solubility characteristics in polar solvents. Precise mapping of this sequence is critical when setting up tandem mass spectrometry (MS/MS) fragmentation patterns during lot verification.
Molecular Weight, Formula, and CAS Registry Parameters
The primary chemical parameters defining Selank free base are as follows: chemical formula $C_{33}H_{57}N_{11}O_9$, exact monoisotopic mass of 751.4341 Da, and an average molecular mass of approximately 751.88 g/mol. When calculating molarity for experimental preparations, researchers must distinguish between the free base molecular weight and the gross molecular weight of the salt form supplied.
Selank is formally registered under the Chemical Abstracts Service (CAS) number 129954-34-3. This unique numerical identifier distinguishes the specific heptapeptide sequence from precursor fragments, metabolic cleavage products, or isomeric derivatives. Investigators sourcing research material can review our verifiable lot-specific COA documentation to verify identity via high-resolution mass spectrometry (HRMS), where the observed $m/z$ ratio corresponds to the expected $[M+H]^+$ ion peak near 752.44 Da.
Salt Forms, Counterions, and Net Peptide Content Determination
Solid-phase peptide synthesis (SPPS) yields peptides as salts due to purification protocols utilizing acidic mobile phases. Selank is typically supplied as an acetate salt ($CH_3COOH$) or trifluoroacetate salt ($CF_3COOH$). The presence of these counterions, along with residual bound moisture (hydration water), means that the total mass of a lyophilized cake contains both the active peptide cation and inactive counterion species.
Net peptide content (NPC) typically ranges between 70% and 85% of total mass, with the remainder composed of counterions and trace bound water. For example, a 10 mg vial of high-purity Selank 10mg with an 80% net peptide content contains 8.0 mg of actual TKPRPGP heptapeptide free base and 2.0 mg of counterions/moisture. To assist bench scientists in converting gross lyophilized mass to precise active peptide concentrations for bioassays, PX1 Research provides an interactive reconstitution calculator to ensure standardized working stock concentrations.
Comparative Analysis: Selank, Semax, and Tuftsin Structural Comparison
To understand the structural class of synthetic regulatory peptides, it is useful to compare Selank against related reference compounds evaluated in neuro-immunology literature. Native tuftsin structural overview consists of the core tetrapeptide sequence Thr-Lys-Pro-Arg (MW ~500.6 g/mol, CAS 9012-71-9), which serves as the biological template for Selank. By comparison, semax molecular weight sequence represents an ACTH(4-10) analog with the heptapeptide sequence Met-Glu-His-Phe-Pro-Gly-Pro (MW ~873.0 g/mol, CAS 80714-61-0), sharing the identical C-terminal Pro-Gly-Pro stabilizing tail with Selank but featuring an entirely distinct N-terminal domain.
While both Selank and Semax incorporate the Pro-Gly-Pro tripeptide sequence to extend enzymatic half-life in vitro, their primary amino acid sequences target distinct cellular signaling mechanisms. Selank's basic amino acids (Lys-2, Arg-4) generate a net positive charge at neural pH, whereas Semax contains acidic (Glu-2) and aromatic (Phe-4) residues that modify its hydrophobic interaction profile. Contrasting these sequence-specific physical properties allows comparative research into peptide-membrane dynamics and receptor binding energetics.
Preclinical Research Scope and In Vitro Mechanism Highlights
In preclinical laboratory models, researchers investigate Selank for its capacity to modulate diverse neurochemical pathways. In vitro assays indicate that the heptapeptide interacts with the GABAergic neurotransmitter system, where it appears to exert allosteric regulatory effects on GABA-A receptor complexes without directly binding to the primary benzodiazepine site. Preclinical rodent models further demonstrate that administration of Selank correlates with altered expression profiles of brain-derived neurotrophic factor (BDNF) in hippocampal tissue culture.
Additionally, preclinical investigations suggest Selank inhibits enkephalin-degrading enzymes (such as neutral endopeptidase and aminopeptidase N) in plasma and brain homogenates. By slowing down the cleavage of endogenous opioid peptides like leu-enkephalin, Selank serves as a useful tool compound for dissecting peptidase activity and endogenous peptide stability in tissue lysates. All such observations are limited to controlled experimental settings.
Analytical Protocol Verification: RP-HPLC and Mass Spectrometry
Ensuring analytical rigor requires robust analytical assays to confirm peptide identity, purity, and sequence fidelity. At PX1 Research, every batch of research material undergoes reversed-phase high-performance liquid chromatography (RP-HPLC) paired with electrospray ionization mass spectrometry (ESI-MS). RP-HPLC separates the main peak from closely eluting synthesis impurities, such as deletion sequences (e.g., des-Pro or des-Gly fragments) and oxidized species.
Chromatographic purity for research-grade Selank must strictly meet or exceed 98.0% by peak area integration at 214 nm and 220 nm (peptide backbone absorption wavelengths). Mass spectrometry confirms the target molecular weight by identifying the primary protonated molecule $[M+H]^+$ at $m/z = 752.44 \pm 0.5$ Da, as well as the doubly charged species $[M+2H]^{2+}$ at $m/z = 376.72 \pm 0.5$ Da. For broader inquiries on analytical standards, explore our research library for protocols on analyzing synthetic regulatory peptides.
Solubility, Storage, and Laboratory Reconstitution Guidelines
Selank is highly soluble in aqueous media due to its basic basic amino acid residues (Lys, Arg) and hydrophilic backbone. For laboratory reconstitution, sterile bacteriostatic water or standard phosphate-buffered saline (PBS, pH 7.4) is recommended. Lyophilized powders should be brought to room temperature prior to reconstituting to prevent moisture condensation inside the vial.
Lyophilized Selank stored at -20°C in a desiccated environment remains stable for extended periods. Once reconstituted into liquid solution, working aliquots should be maintained at 2°C to 8°C for short-term handling or sub-aliquoted and stored at -80°C to prevent freeze-thaw degradation cycles. Avoid energetic vortexing, as shear forces can disrupt peptide bond geometry or cause physical aggregation in solution. For detailed protocols regarding salt calculations and bulk liquid handling, laboratory administrators can consult our wholesale account specialists.
PX1 Research Quality Assurance & Manufacturing Standards
PX1 Research operates strictly as a supplier of USA-manufactured research peptides designed exclusively for non-clinical laboratory use. Every production lot is synthesized in accordance with state-of-the-art solid-phase methodologies within GMP-compliant facilities and tested by an independent, ISO 17025-accredited analytical laboratory.
In addition to RP-HPLC purity and ESI-MS sequence identity validation, PX1 Research subjects all batches to quantitative bacterial endotoxin testing (LAL assay) to ensure suitability for sensitive cell culture and in vitro biochemical systems. Orders placed Monday through Friday ship same-day from our fulfillment facilities located in California and Arizona, providing research teams with reliable, batch-consistent reference standards.
Frequently Asked Questions
What is the exact molecular weight and chemical formula of Selank?
Selank (free base) has a molecular formula of C33H57N11O9 and an average molecular weight of approximately 751.88 g/mol (monoisotopic mass: 751.4341 Da). The gross weight of a salt formulation (e.g., acetate) will be higher depending on the counterion ratio.
What is the amino acid sequence of Selank?
The amino acid sequence of Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro (single-letter code: TKPRPGP). It consists of seven L-amino acid residues, combining the tuftsin tetrapeptide core with a stabilizing C-terminal Pro-Gly-Pro tripeptide.
What is the CAS registry number for Selank?
Selank is assigned the Chemical Abstracts Service (CAS) registry number 129954-34-3.
How does counterion salt content affect peptide calculations in the laboratory?
Synthetic peptides exist as counterion salts (such as acetate or TFA). The net peptide content (NPC) usually represents 70% to 85% of total lyophilized mass. Researchers must account for NPC when preparing precise molar solutions for quantitative in vitro bioassays.
How should lyophilized Selank be stored in a laboratory setting?
Lyophilized Selank powder should be stored desiccated at -20°C or -80°C for long-term stability. Upon reconstitution in aqueous buffer, solutions should be sub-aliquoted and stored at -80°C to prevent structural degradation from repeated freeze-thaw cycles.
What analytical methods are used to verify Selank purity?
Purity and identity are verified using Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC) to assess purity (typically ≥98%) and Electrospray Ionization Mass Spectrometry (ESI-MS) to confirm sequence molecular weight.
Is Selank suitable for human or veterinary administration?
No. Selank supplied by PX1 Research is strictly a research chemical designated for in vitro, biochemical, and laboratory investigation only. It is not for human, clinical, therapeutic, or veterinary use.
What is the structural relationship between Selank and Tuftsin?
Selank is a direct structural derivative of the endogenous immune tetrapeptide tuftsin (Thr-Lys-Pro-Arg). The addition of the C-terminal Pro-Gly-Pro sequence enhances peptide stability against carboxypeptidase degradation in biological experimental matrices.
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