Peptide Handbook

This handbook is published in the United Kingdom for the in-vitro scientific research community. All materials referenced are unlicensed research chemicals supplied solely for laboratory investigation, analytical reference and educational study. They are not medicinal products within the meaning of the Human Medicines Regulations 2012 (SI 2012/1916) and have no marketing authorisation from the Medicines and Healthcare products Regulatory Agency (MHRA). They are not intended for administration to humans or animals, are not food, cosmetics or dietary supplements, and must not be represented as such. SPT PEPTIDE does not provide, and this handbook does not contain, clinical, diagnostic, prescribing, dosing or therapeutic guidance. Customers must be aged 18 or over and must use the materials in compliance with the Health and Safety at Work etc. Act 1974, COSHH Regulations 2002, and any institutional ethics or biosafety approvals applicable to their work.

Peptides are short chains of amino acids — typically 2 to 50 residues — joined by peptide bonds. They differ from proteins primarily in length and tertiary folding complexity. In biological systems peptides function as hormones (insulin, glucagon, oxytocin), neurotransmitters (substance P, enkephalins), growth factors (IGF-1 fragments) and signalling molecules that bind selectively to G-protein-coupled receptors (GPCRs) or tyrosine-kinase receptors. Research peptides are produced via solid-phase peptide synthesis (SPPS, Merrifield 1963) and purified by reverse-phase HPLC, typically to ≥98% purity.

Most peptide ligands signal through GPCRs (Class A rhodopsin-like, Class B secretin-like) or single-pass tyrosine-kinase receptors. Class B GPCRs — including GLP-1R, GIPR, GCGR, GHRHR and PTHR1 — share a large extracellular domain that captures the peptide's C-terminal helix before the N-terminus engages the transmembrane bundle (the 'two-domain' binding model). Downstream signalling typically proceeds via Gαs/cAMP/PKA, with β-arrestin recruitment driving receptor internalisation and biased agonism — a major axis of modern peptide drug discovery.

The incretin family includes semaglutide, liraglutide, tirzepatide (GLP-1/GIP dual agonist) and retatrutide (GLP-1/GIP/glucagon triple agonist). They mimic endogenous glucagon-like peptide-1, slowing gastric emptying, increasing glucose-dependent insulin secretion from pancreatic β-cells and acting centrally on arcuate POMC neurons. Retatrutide adds glucagon-receptor agonism, which in preclinical models drives additional energy expenditure via hepatic and brown-adipose pathways (Coskun et al., Cell Metab 2022). Semaglutide and tirzepatide are licensed medicines in the UK (Ozempic®, Wegovy®, Mounjaro®) prescribed only under MHRA marketing authorisation — research-grade analogues sold here are unlicensed reference compounds for in-vitro study.

GHRPs (GHRP-2, GHRP-6, ipamorelin, hexarelin) bind the ghrelin/GHS-R1a receptor to trigger pituitary GH release in animal models. GHRH analogues (sermorelin, tesamorelin, CJC-1295) act on the GHRH receptor. CJC-1295 with DAC has an extended half-life via covalent albumin binding. The literature on combined GHRH + GHRP signalling (e.g. CJC-1295 + ipamorelin) describes synergistic, pulsatile GH release in preclinical systems (Sigalos & Pastuszak, Sex Med Rev 2018).

BPC-157 is a 15-amino-acid synthetic peptide originally derived from a fragment of gastric juice protein BPGP. Preclinical literature describes upregulation of VEGFR2, modulation of nitric-oxide synthesis and accelerated tendon, ligament and gut-mucosal healing in rodent models (Sikiric et al., Curr Pharm Des 2018). TB-500 is a synthetic fragment of thymosin β-4 (residues 17-23, LKKTETQ) studied for actin sequestration and endothelial cell migration. Note: the European Medicines Agency lists BPC-157 as not authorised as a medicine anywhere in the EU/UK and has issued statements warning against unlicensed human use.

Melanotan-II and PT-141 (bremelanotide) are non-selective MC1R/MC3R/MC4R agonists. MC1R activation drives eumelanogenesis via cAMP/MITF. MC4R activation in the hypothalamic paraventricular nucleus is implicated in appetite and arousal pathways. PT-141 is approved in the United States (Vyleesi®) for HSDD in premenopausal women but holds no MHRA marketing authorisation in the UK. The MHRA and UK Trading Standards have repeatedly warned against the sale of melanotan products for tanning use.

Semax and Selank are heptapeptide analogues of ACTH(4-10) and tuftsin respectively, developed at the Russian Academy of Sciences. Both modulate BDNF expression in the hippocampus and demonstrate anxiolytic and neuroprotective effects in rodent models (Kolomin et al., Curr Drug Discov Technol 2013). Cerebrolysin and Dihexa are studied for hepatocyte-growth-factor-like activity at neuronal synapses. None are licensed medicines in the United Kingdom.

SS-31 (elamipretide) is a tetrapeptide that binds cardiolipin on the inner mitochondrial membrane, stabilising electron-transport-chain supercomplexes and reducing reactive oxygen species (Szeto, Br J Pharmacol 2014). MOTS-c is a 16-aa mitochondrial-derived peptide encoded within the 12S rRNA gene; it activates AMPK and improves insulin sensitivity in murine models (Lee et al., Cell Metab 2015). Epitalon is a tetrapeptide (Ala-Glu-Asp-Gly) studied in vitro for telomerase modulation.

Thymosin α-1 (Zadaxin®) is a 28-aa peptide that promotes T-cell maturation via TLR9/MyD88 signalling and is licensed in 35+ countries — though not currently the UK — for hepatitis B and as a vaccine adjuvant. LL-37 (cathelicidin) is the human host-defence peptide with broad antimicrobial and immunomodulatory activity studied across infection, wound and oncology models.

Research peptides should be supplied lyophilised, sealed under inert gas, with a Certificate of Analysis (CoA) showing: (i) reverse-phase HPLC purity ≥98%, (ii) ESI- or MALDI-TOF mass-spectrometry confirmation of molecular weight within ±1 Da of theoretical, (iii) where relevant, bacterial-endotoxin quantification by LAL, and (iv) batch and synthesis-date traceability. Acetate counter-ion and residual TFA content should be disclosed for amphipathic sequences. SPT batches are tested to ≥99% HPLC purity where chemistry allows.

Lyophilised peptide is typically stable at −20 °C for 24+ months and at −80 °C for the long term, protected from light and moisture. Allow vials to equilibrate to room temperature before opening to prevent atmospheric-water condensation onto the powder. Reconstitution solvents are sequence-dependent: most amphipathic sequences dissolve in sterile or bacteriostatic water; hydrophobic sequences may require dilute acetic acid or DMSO. Once in solution, most peptides retain analytical potency for 14–28 days at 2–8 °C. Always work within a risk assessment compliant with COSHH 2002 and your institution's biosafety policy; treat all unknown biological material as potentially hazardous and dispose of sharps and residues via licensed clinical-waste streams.

Within the UK, only peptides holding an MHRA marketing authorisation may be marketed, supplied or administered as medicines. As of publication, this includes (non-exhaustive) semaglutide, liraglutide, tirzepatide, octreotide, desmopressin, teriparatide, oxytocin and certain insulin analogues — each available only via a registered prescriber and pharmacy. All other peptides referenced in this handbook (BPC-157, TB-500, GHRPs, CJC-1295, MOTS-c, SS-31, Epitalon, Semax, Selank, Melanotan-II, PT-141, Thymosin α-1, retatrutide and similar) hold no UK marketing authorisation and are supplied solely as unlicensed reference compounds for in-vitro laboratory research. Supplying or representing any unlicensed peptide for human use is an offence under Regulation 46 of the Human Medicines Regulations 2012.

Before purchasing or working with any research peptide: (1) confirm you are 18 or over and ordering on behalf of a bona-fide research, academic, analytical or educational project; (2) record the intended in-vitro application in your laboratory notebook or LIMS; (3) review the manufacturer's CoA and Safety Data Sheet (SDS) and incorporate hazards into a written COSHH assessment; (4) store material under the conditions on the CoA; (5) never administer research-grade material to humans or animals; (6) dispose of unused material via a licensed waste contractor; (7) keep purchase records for a minimum of 12 months for audit and traceability.