This is a working overview of Freeze-thaw cycle, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-01-04. Anything still debated is marked as such rather than presented as settled.
The compound entered scientific literature in the 1970s, when plasma factors with copper-binding activity were isolated and characterized. Later work expanded into wound healing, skin biology, and cosmetic formulation, where copper tripeptide-1 became a recognized ingredient name. Most published studies remain preclinical or small-scale, and findings are often reported in specialized dermatology or peptide journals. Regulatory treatment varies: some jurisdictions allow it as a cosmetic ingredient, while research-grade material is sold for laboratory use. Questions about optimal delivery, target tissues, and long-term effects continue to be investigated rather than settled.
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.
The International Nomenclature of Cosmetic Ingredients lists the substance as copper tripeptide-1, the name that appears on most topical product labels. Related designations include copper peptide and GHK-Cu, and the hyphenated form is common in research literature. In cosmetics the material is regulated as an ingredient rather than as a drug, so products may reach the market without evidence of the effects claimed for them. Whether those effects are clinically meaningful is an open question, since most supportive data come from laboratory work and small trials.
GHK-Cu is the copper complex of the tripeptide glycyl-L-histidyl-L-lysine, a short sequence found naturally in human plasma, saliva and urine. Loren Pickart reported the isolation of the free peptide in 1973 while studying factors that influenced the growth of aged liver cells in culture. The peptide was later shown to bind copper(II) with high affinity, and the metal-bound form became the focus of most subsequent research. Its concentration in circulation declines markedly with age, a pattern that is well documented, though the physiological consequences of that decline remain debated.
The peptide portion consists of three amino acids: glycine, histidine and lysine. Copper(II) coordinates through the imidazole nitrogen of histidine, the alpha-amino group of glycine and a deprotonated amide nitrogen of the backbone, producing a roughly square-planar geometry. This arrangement gives the complex its characteristic blue-to-violet colour and helps it resist dissociation in water. Reported stability constants are high, although values differ between studies because of differences in ionic strength and measurement method.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Copper-binding tripeptide complex | Includes Gly-His-Lys and Cu(II) |
| Molecular formula | C14H22CuN6O4 | Reported for the 1:1 complex |
| Appearance | Blue to blue-violet solid | Color arises from copper d-d transitions |
| Solubility class | Water-soluble; slightly soluble in polar organic solvents | Often prepared as aqueous stock |
| Typical storage | -20 °C, desiccated, protected from light | Limits oxidation and moisture uptake |
The molecular weight and charge of GHK-Cu depend on the pH and the number of coordinated ligands. At neutral pH, the peptide typically binds one copper ion, but ternary complexes with other biomolecules can form. Spectroscopic methods such as electron paramagnetic resonance and circular dichroism are used to study the coordination environment. Reports on the exact geometry vary because the complex is dynamic in solution. Researchers often use synthetic GHK-Cu rather than extracted material to control stoichiometry and purity.
GHK-Cu is a coordination complex formed from the tripeptide glycyl-L-histidyl-L-lysine and a copper(II) ion. The peptide binds copper through its histidine imidazole nitrogen, the terminal amino group, and the deprotonated amide nitrogen. This arrangement creates a square-planar or distorted geometry around the metal center, depending on pH and the presence of competing ligands. The complex occurs naturally in human plasma, saliva, and urine at low concentrations, and its sequence is conserved across many vertebrate species.
Discovery of GHK is generally attributed to work in the 1970s that isolated a plasma factor influencing liver cell behavior. Subsequent studies identified the copper-binding tripeptide and its ability to chelate copper with high affinity. Early reports linked the complex to wound healing and tissue remodeling in animal models. The free peptide and the copper-bound form have different properties, so the two are distinguished in the literature. Whether endogenous GHK-Cu serves a single primary physiological role remains an open question.
Identity and purity are established with a combination of chromatographic and spectroscopic techniques. Reversed-phase high-performance liquid chromatography separates the intact complex from peptide fragments and free copper, and the elution profile yields a purity estimate. Mass spectrometry gives the mass of the intact species and exposes degradation products. Ultraviolet-visible spectroscopy displays a broad absorption band in the visible region that is characteristic of the copper center. Nuclear magnetic resonance is less informative here, because the paramagnetic metal broadens signals and complicates spectral interpretation.
Copper content is measured separately, since a peptide assay alone does not report the metal-to-peptide ratio. Elemental techniques such as inductively coupled plasma optical emission spectroscopy quantify copper after acid digestion of the sample. The result is compared with the theoretical value for a one-to-one complex, and a shortfall indicates free peptide or partial dissociation. Suppliers differ in how they state purity, as some quote peptide content and others quote the whole complex. A defined stoichiometry therefore requires both a peptide assay and a copper assay.
Solid GHK-Cu is usually supplied as a lyophilized powder and is kept cold and dry. Moisture, light, and repeated temperature cycling shorten its useful life in the laboratory. In aqueous solution the complex undergoes slow hydrolysis of the peptide backbone and gradual loss of coordinated copper. Buffers containing strong chelators, such as EDTA, compete for the metal and strip it from the peptide. Working solutions are therefore prepared shortly before use, and leftover liquid is not returned to the stock container.
Laboratory characterization of GHK-Cu typically combines separation, spectroscopic, and elemental techniques. Reverse-phase high-performance liquid chromatography is widely used to assess peptide purity, often with ultraviolet detection near the copper-related absorption band or with mass spectrometry for identity confirmation. Because the molecule contains copper, elemental methods such as inductively coupled plasma mass spectrometry or atomic absorption spectroscopy are used to quantify metal content and confirm stoichiometry. No single universal pharmacopeial monograph exists for GHK-Cu. Laboratories therefore validate their own methods, and reported purity values depend on the chosen assay and calibration standards.
Stability of GHK-Cu is influenced by light, oxygen, moisture, pH, and temperature. Solid material is generally kept desiccated and frozen to reduce hydrolysis and oxidation, while aqueous solutions are best prepared fresh or stored cold in aliquots. Repeated freeze-thaw cycles can promote aggregation, precipitation, or peptide degradation. Copper coordination may change under strongly acidic or alkaline conditions, potentially altering the complex's spectroscopic properties. Published long-term stability data for specific matrices, such as cosmetic emulsions or biological buffers, are limited, so shelf-life claims should be treated as formulation-specific rather than universal.
A PSMA scan is a nuclear medicine imaging technique used in the diagnosis and staging of prostate cancer. It is carried out by injection of a radiopharmaceutical with a positron or gamma emitting radionuclide and a prostate-specific membrane antigen (PSMA) targeting ligand. After injection, imaging of positron emitters such as gallium-68 (68Ga), copper-64 (64Cu), and fluorine-18 (18F) is carried out with a positron emission tomography (PET) scanner. For gamma emitters such as technetium-99m (99mTc) and indium-111 (111In) single-photon emission computed tomography (SPECT) imaging is performed with a gamma camera. As well as the diagnosis and staging of prostate cancer, PSMA imaging can also be used to assess suitability for and plan treatment with external beam radiotherapy and PSMA-targeted radionuclide therapy.
However, Waley also testified that majority rule was not desirable immediately. Talks aimed at easing the differences between Rhodesia and the United Kingdom were carried out aboard Royal Navy vessels once in December 1966 and again in October 1968. Both efforts failed to achieve agreement, although Harold Wilson added a sixth principle to the five he had previously enunciated: "it would be necessary to ensure that, regardless of race, there was no oppression of the majority by the minority or of [any] minority by the majority." Rhodesian resolve stiffened following a failure to reach a new settlement, with more radical elements of the Rhodesian Front calling for a republican constitution. During a two-proposition referendum held in 1969, the proposal for severing all remaining ties to the British Crown passed by a majority of 61,130 votes to 14,327. Rhodesia declared itself a republic on 2 March 1970. Under the new constitution, a president served as ceremonial head of state, with the prime minister nominally reporting to him. Some in the Rhodesian government had hoped in vain that the declaration of a republic would finally prompt other nations to grant recognition.
Derived structure parameters that describe constant properties of the overall feedback control system may add useful information for special purposes, e.g. in diagnosis of nonthyroidal illness syndrome or central hypothyroidism.
== Interactions == Vardenafil should not be used by people taking nitrate medications, because combining them with vardenafil might provoke potentially life-threatening hypotension (low blood pressure). Further, vardenafil causes lengthening of the QT interval. Therefore, it should not be taken by people taking other medications that affect the QT interval (such as amiodarone).
=== Other lymphomas and squamous-cell carcinoma === In September 2022, the FDA announced new information regarding other types of cancers related to breast implants, based on medical device reports (MDRs) of cases of patients with squamous-cell carcinoma or various lymphomas found in the scar tissue around breast implants. The agency reported 10 MDRs about squamous-sell carcinoma found in the capsule scar tissue and 12 MDRs about various lymphomas also in the scar tissue around the breast implants. These new cases do not overlap with cases of BIA-ALCL. SCC and other lymphomas have been found in smooth-surface and textured implants as well as silicone-gel-filled and saline-filled implants. Patients who reported symptoms specified swelling, pain, lumps, and changes to their skin. As of 2022, neither the incidence rate nor prevalence is known.
Sources: en.wikipedia.org
Tris, or tris(hydroxymethyl)aminomethane, or known during medical use as tromethamine or THAM, is an organic compound with the formula (HOCH2)3CNH2. It is extensively used in biochemistry and molecular biology as a component of buffer solutions such as in TAE and TBE buffers, especially for solutions of nucleic acids. It contains a primary amine and thus undergoes the reactions associated with typical amines, e.g., condensations with aldehydes. Tris also complexes with metal ions in solution. In medicine, tris (known as tromethamine) is occasionally used as a drug, given in intensive care for its properties as a buffer for the treatment of severe metabolic acidosis in specific circumstances. Some medications are formulated as the "tromethamine salt" including Hemabate (carboprost as trometamol salt), and "ketorolac trometamol". In 2023 a strain of Pseudomonas hunanensis was found to be able to degrade TRIS buffer. Since Tris's pKa is more strongly temperature dependent, its use is not recommended in biochemical applications requiring consistent pH over a range of temperatures. Moreover, the temperature dependence of the pKa (and in turn buffer solution pH) makes pH adjustment difficult. (E.g., the 'room temperature' pH adjustment would not translate to 'measurement conditions' pH, unless care is taken to calculate the effect of temperature, see below.)
Electrical stimulation using implantable devices came into modern usage in the 1980s, and its techniques and applications have continued to develop and expand. These are methods where an operation is required to position an electrode. The stimulator, with the battery, similar to a pacemaker, may also be implanted, or may remain outside the body. In general, neuromodulation systems deliver electrical currents and typically consist of the following components: An epidural, subdural, or parenchymal electrode placed via minimally invasive needle techniques (so-called percutaneous leads) or an open surgical exposure to the target (surgical "paddle" or "grid" electrodes), or stereotactic implants for the central nervous system, and an implanted pulse generator (IPG). Depending on the distance from the electrode access point, an extension cable may also be added into the system. The IPG can have either a non-rechargeable battery needing replacement every 2–5 years (depending on stimulation parameters) or a rechargeable battery that is replenished via an external inductive charging system. Although most systems operate via delivery of a constant train of stimulation, there has recently been an emergence of so-called "feed-forward" stimulation, in which the device's activation is contingent on a physiological event, such as an epileptic seizure. In this circumstance, the device is activated and delivers a desynchronizing pulse to the cortical area that is undergoing an epileptic seizure.
The two substrates of this enzyme are D-xylose and oxidised nicotinamide adenine dinucleotide phosphate (NADP+). Its products are D-xylono-1,5-lactone, reduced NADPH, and a proton. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is D-xylose:NADP+ 1-oxidoreductase. Other names in common use include D-xylose (nicotinamide adenine dinucleotide phosphate), dehydrogenase, D-xylose-NADP+ dehydrogenase, D-xylose:NADP+ oxidoreductase, and D-xylose 1-dehydrogenase (NADP+).
=== Ehlers–Danlos syndrome hypermobility type === Joint hypermobility is often correlated with hypermobile Ehlers–Danlos syndrome (hEDS, known also by EDS type III or Ehlers–Danlos syndrome hypermobility type (EDS-HT)). Ehlers–Danlos syndrome is a genetic disorder caused by mutations or hereditary genes, but the genetic defect that produces hEDS is largely unknown. In conjunction with joint hypermobility, a common symptom for hEDS is smooth, velvety, and stretchy skin. When diagnosing hEDS, the Beighton Criteria are used, but are not always able to distinguish between joint hypermobility syndrome and hEDS. Ehlers–Danlos hypermobility type can have severe musculoskeletal effects, including:
Creatine kinase S-type, mitochondrial is an enzyme that in humans is encoded by the CKMT2 gene. Mitochondrial creatine kinase (MtCK) is responsible for the transfer of high energy phosphate from mitochondria to the cytosolic carrier, creatine. The "energy-rich" gamma-phosphate group of ATP that is generated by oxidative phosphorylation inside mitochondria is trans-phosphorylated to creatine (Cr) to give phospho-creatine (PCr), which then is exported from the mitochondria into the cytosol, where it is made available to cytosolic creatine kinases (CK) for in situ regeneration of the ATP that has been used for cellular work. Cr then is returning to the mitochondria where it stimulates mitochondrial respiration and again is charged-up by mitochondrial ATP via MtCK. This process is termed the PCr/Cr-shuttle or circuit. MtCK belongs to the creatine kinase (CK) isoenzyme family. It exists as two isoenzymes, sarcomeric MtCK and ubiquitous MtCK, encoded by separate genes. Mitochondrial creatine kinase occurs in two different oligomeric forms: dimers and octamers, in contrast to the exclusively dimeric cytosolic creatine kinase isoenzymes. Sarcomeric mitochondrial creatine kinase has 80% homology with the coding exons of ubiquitous mitochondrial creatine kinase. This gene contains sequences homologous to several motifs that are shared among some nuclear genes encoding mitochondrial proteins and thus may be essential for the coordinated activation of these genes during mitochondrial biogenesis.
Sources: en.wikipedia.org
== Applications == The shikimate pathway is a target for herbicides and other non-toxic drugs because the shikimate pathway is not present in humans. Glyphosate, a commonly used herbicide, is an inhibitor of 5-enolpyruvylshikimate 3-phosphate synthase or EPSP synthase, an enzyme in the shikimate pathway. The problem is that this herbicide has been utilized for about 20 years and now some plants have now emerged that are glyphosate-resistant. This has relevance to research on shikimate dehydrogenase because it is important to maintain diversity in the enzyme blocking process in the shikimate pathway and with more research shikimate dehydrogenase could be the next enzyme to be inhibited in the shikimate pathway. In order to design new inhibitors the structures for all the enzymes in the pathway have needed to be elucidated. The presence of two forms of the enzyme complicate the design of potential drugs because one could compensate for the inhibition of the other. Also there the TIGR data base shows that there are 14 species of bacteria with the two forms of shikimate dehydrogenase. This is a problem for drug makers because there are two enzymes that a potential drug would need to inhibit at the same time.
==== Papillary region ==== The papillary region is composed of loose areolar connective tissue. It is named for its finger-like projections called papillae, which extend toward the epidermis. The papillae provide the dermis with a "bumpy" surface that interdigitates with the epidermis, strengthening the connection between the two layers of skin. In the palms, fingers, soles, and toes, the influence of the papillae projecting into the epidermis forms contours in the skin's surface. These epidermal ridges occur in patterns (see: fingerprint) that are genetically and epigenetically determined and are therefore unique to the individual, making it possible to use fingerprints or footprints as a means of identification.
=== Self-harm and suicidality === Self-harm and suicidal behaviors are core diagnostic criteria for BPD as outlined in the DSM-5. Between 50% and 80% of individuals diagnosed with BPD engage in self-harm, with cutting being the most common method. Other methods, such as bruising, burning, head banging, or biting, are also prevalent. It is hypothesized that individuals with BPD might experience a sense of emotional relief following acts of self-harm. The motivations behind self-harm and suicide attempts among individuals with BPD are reported to differ. Nearly 70% of individuals with BPD engage in self-harm without the intention of ending their lives. Motivations for self-harm include expressing anger, self-punishment, inducing normal feelings or feelings of normality in response to dissociative episodes, and distraction from emotional distress or challenging situations. Conversely, true suicide attempts by individuals with BPD are frequently motivated by the notion that others will be better off in their absence.
Cottage cheese is a type of fresh cheese with a mild flavor and a creamy, heterogeneous texture made from skimmed milk – hence the low milkfat content. It is made by adding an acid – like vinegar or lemon juice – to the milk which causes the milk proteins (curds) to separate from the liquid (whey). The curds are then drained and mixed with cream and salt, giving cottage cheese its slightly tangy taste and creamy texture. The addition of a "dressing" to the curd grains is primarily responsible for the taste of the finished food. Cottage cheese is not aged. It was first called 'cottage cheese' in 1831, likely originating from Pennsylvania Dutch immigrants making cheese curds to spread on snacks in their homesteads (cottages). Cottage cheese can be relatively low in milkfat and calories for the high amount of protein it provides, and is a rich source of vitamin B12. Cottage cheese comes in different fat levels, including low–fat and fat–free – but even an original 'full fat' version has fewer calories than a chunk of hard cheese or wedge of soft cheese. Cottage cheese is a versatile nutritious food readily added to fruit, vegetables, bread and breakfast items, pastas, sauces, and desserts.
Sources: en.wikipedia.org
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.
Yes, the peptide and its copper complex have been detected in human plasma, saliva, and urine. Endogenous concentrations are low, and reported levels change with age and physiological state. The biological significance of those changes is still an active area of study.
GHK refers to the free tripeptide without a bound copper ion. GHK-Cu contains copper(II) coordinated to the same peptide backbone. The presence of copper affects the complex's color, stability, and interaction with biological molecules.
It is a complex of a three-amino-acid peptide, glycine, histidine and lysine, bound to a single copper(II) ion. The metal is held mainly by the histidine side chain and the peptide backbone. Most commercial material is supplied as an acetate salt rather than as the free complex.