Endogenous peptide comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2026-04-05. Where a claim depends on a specific study, the study is described rather than over-claimed.
GHK-Cu is a coordination complex formed between the peptide glycyl-L-histidyl-L-lysine and a copper(II) ion. The unbound chain, abbreviated GHK, consists of three amino acids and occurs naturally in human plasma, saliva, and urine. Binding of the metal is mediated mainly by the imidazole nitrogen of the histidine residue together with backbone amides, producing a stable chelate. Ingredient nomenclature often lists the same substance as copper tripeptide-1. Its charge and solubility behaviour differ from those of the metal-free chain.
The copper-binding activity of this sequence was described in the 1970s during studies of liver tissue and plasma factors. Early work identified the peptide as a component that influenced copper uptake by cells and that appeared in wound fluid. Later investigations examined its presence across species, reporting the same chain in human and animal samples. A decline in measured concentration with age became a recurring observation, although the underlying causes remain incompletely characterised.
GHK-Cu is a coordination complex formed between the tripeptide glycyl-L-histidyl-L-lysine and a copper(II) ion. The peptide sequence is often abbreviated Gly-His-Lys, and the copper is bound through the histidine imidazole nitrogen and adjacent peptide nitrogens. The complex is frequently described as a 1:1 peptide-to-copper species. It occurs naturally in human plasma, saliva, and urine at low concentrations. Its endogenous levels have been reported to decline with age, although the precise physiological role of that change remains an open question.
Research interest in GHK-Cu centers on its ability to deliver copper and to influence cellular processes in laboratory models. In cell culture and animal studies, the complex has been linked to collagen synthesis, antioxidant enzyme activity, and expression of genes associated with tissue remodeling. These effects are not equivalent to proven clinical outcomes. The mechanisms proposed include copper transfer to cuproenzymes, modulation of growth factor signaling, and interactions with extracellular matrix components. How much of the observed activity depends on intact GHK-Cu versus free copper or free peptide is not fully resolved.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Copper(II) peptide complex | Coordination compound rather than a simple salt |
| Peptide sequence | Glycyl-L-histidyl-L-lysine | Abbreviated GHK in most literature |
| Molecular formula | C14H22N6O4Cu | Reported for the 1:1 complex |
| Principal binding site | Histidine imidazole nitrogen | Backbone amides contribute additional coordination |
| Common synonym | Copper tripeptide-1 | Used in ingredient and product labelling |
Copper binds to the peptide through the histidine imidazole nitrogen and the terminal amino group, forming a stable square-planar complex. Binding constants reported for copper(II) with GHK are high, so the peptide competes effectively for copper in solution. The complex absorbs visible light, which gives solutions a blue to violet colour. Whether the metal-free peptide has a distinct biological function of its own is still an open question; some work treats it mainly as a copper delivery vehicle, while other work reports peptide-specific effects.
The compound was first isolated from human plasma in the 1970s by Loren Pickart, who later described copper-binding activity in liver and other tissues. Early reports focused on its presence in blood and its ability to carry copper between proteins. Commercial and cosmetic use of the term 'copper peptide' has since broadened, and labels rarely distinguish GHK-Cu from other copper-binding fragments. This naming overlap makes literature searching harder, because cosmetic ingredient lists, supplier catalogues and laboratory papers use different vocabularies for the same molecule.
Identity and purity are assessed mainly by reversed-phase high-performance liquid chromatography with ultraviolet detection, often paired with mass spectrometry to confirm the expected mass. Copper content is measured separately by inductively coupled plasma optical emission spectrometry or atomic absorption spectroscopy, because the peptide assay alone does not establish the metal-to-peptide ratio. Visible spectroscopy provides a rapid check on complex integrity through the absorption band in the visible region. Agreement between the peptide assay and the copper assay is the practical test of whether a sample is the intended complex rather than a mixture.
Aqueous solutions of GHK-Cu are less stable than the dry powder. The peptide backbone is vulnerable to hydrolysis at extreme pH, and copper can be stripped from the complex by strong chelating agents such as EDTA or citrate. Oxidising agents and high concentrations of ascorbic acid can reduce copper(II) and change the complex, which is one reason formulators often keep such ingredients in separate phases. How quickly these changes occur under real storage conditions depends on pH, buffer, temperature and packaging, and quantitative data on the subject are limited.
Dry material is normally held cold, commonly at -20 °C for long-term storage and 2 to 8 °C for working quantities, protected from light and moisture. Vials should be allowed to reach room temperature before opening so that condensation does not form on the powder. In liquid formulations the complex is generally kept near neutral to slightly acidic pH, because strongly alkaline conditions favour precipitation of copper hydroxide. Antioxidants or chelate-stabilising excipients are often added, though the specific approaches are proprietary and rarely published in detail.
== Diagnosis == Acanthosis nigricans is typically diagnosed clinically based on its characteristic velvety hyperpigmentation and distribution. A skin biopsy is rarely needed but, when performed, shows hyperkeratosis, papillomatosis and mild basal hyperpigmentation. Evaluation aims to identify associated conditions. Investigations may include:
The relationship between sex steroids and SHBG in physiological and pathological conditions is complex, as various factors may influence the levels of plasma SHBG, affecting bioavailability of testosterone.
=== Redox === Hydroquinone can be reversibly oxidised under mild conditions to give benzoquinone. Naturally occurring hydroquinone derivatives, such as coenzyme Q, exhibit similar reactivity, wherein one hydroxyl group is exchanged for an amino group. Given the conditional reversibility and relative ubiquity of reagents, oxidation reactions of hydroquinones and hydroquinone derivatives are of significant commercial use, often used at an industrial scale. When colorless hydroquinone and benzoquinone—bright yellow in solid form—are cocrystallized at a 1:1 ratio, a dark-green crystalline charge-transfer complex (melting point 171 °C), known as quinhydrone (C6H6O2·C6H4O2), is formed. This complex dissolves in hot water, dissociating both quinone molecules in solution.
Sources: en.wikipedia.org
=== Bibliography === Wiseman A (1993). "Designer enzyme and cell applications in industry and in environmental monitoring". J Chem Technol Biotechnol. 56 (1): 3–13. Bibcode:1993JCTB...56....3W. doi:10.1002/jctb.280560103. PMID 7763363. Diekmann S, Weston J, Anders E, et al. (April 2002). "Metal-mediated reactions modeled after nature". J. Biotechnol. 90 (2): 73–94. doi:10.1016/s1389-0352(01)00067-8. PMID 12069195.
=== EC 1.13.99 Miscellaneous === EC 1.13.99.1: inositol oxygenase EC 1.13.99.2: Now EC 1.14.12.10, benzoate 1,2-dioxygenase EC 1.13.99.3: tryptophan 2′-dioxygenase EC 1.13.99.4: Now EC 1.14.12.9, 4-chlorophenylacetate 3,4-dioxygenase EC 1.13.99.5: now EC 1.13.11.47, 3-hydroxy-4-oxoquinoline 2,4-dioxygenase
After Rojas' deposition, the Colombian Conservative Party and the Colombian Liberal Party agreed to create the National Front, a coalition that would jointly govern the country. Under the deal, the presidency would alternate between conservatives and liberals every 4 years for 16 years; the two parties would have parity in all other elective offices. The National Front ended "La Violencia", and National Front administrations attempted to institute far-reaching social and economic reforms in cooperation with the Alliance for Progress. Despite the progress in certain sectors, many social and political problems continued, and guerrilla groups were formally created such as the FARC, the ELN and the M-19 to fight the government and political apparatus. Since the 1960s, the country has suffered from an asymmetric low-intensity armed conflict between government forces, leftist guerrilla groups and right wing paramilitaries. The conflict escalated in the 1990s, mainly in remote rural areas. Since the beginning of the armed conflict, human rights defenders have fought for the respect for human rights, despite staggering opposition. Several guerrillas' organizations decided to demobilize after peace negotiations in 1989–1994. The United States has been heavily involved in the conflict since its beginnings, when in the early 1960s the U.S. government encouraged the Colombian military to attack leftist militias in rural Colombia. This was part of the U.S. fight against communism.
Daniel Joshua Drucker (born 23 June 1956) is a Canadian endocrinologist renowned for his breakthrough discoveries of the biological actions of glucagon-like peptides GLP-1 and GLP-2, including GLP-1's key role in stimulating glucose-dependent insulin secretion, reducing food intake, protecting the heart, and reducing systemic inflammation. His scientific research has been a driving force in GLP-1's journey from a newly discovered peptide sequence to the mechanism behind globally used and life-changing therapeutics for type 2 diabetes and obesity. It has also driven transformative new therapeutics for intestinal failure and other metabolic disorders. A Fellow of the Royal Society, and laureate of the 2023 Wolf Prize in Medicine, he is a University Professor of Medicine at the University of Toronto and Senior Investigator at the Lunenfeld-Tanenbaum Research Institute, Sinai Health, Toronto.
Sources: en.wikipedia.org
GHK denotes the unbound chain of three amino acids. GHK-Cu describes the form in which a copper(II) ion is held by that chain. The two are not interchangeable in solution, since charge, molecular weight, and reactivity differ.
The chain occurs in human plasma, saliva, and urine. Measured amounts are reported to fall with age. Copper binding by the sequence is treated as part of normal metal handling in tissue.
The bound copper(II) centre contributes to redox behaviour and to stability under physiological conditions. Free copper ions can participate in reactions that generate reactive species, while chelated metal is generally more controlled. The chain may also serve as a carrier for copper in experimental systems.
GHK-Cu is a complex of the tripeptide glycyl-L-histidyl-L-lysine with copper(II). The peptide binds copper through its histidine residue and neighboring amide nitrogens, forming a stable coordination compound. It is studied as a research chemical and used in some cosmetic formulations.