# Denaturation (biochemistry)

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Loss of structure in proteins and nucleic acids due to external stress

[IUPAC](/source/International_Union_of_Pure_and_Applied_Chemistry) definition

Process of partial or total alteration of the native secondary, and/or tertiary, and/or quaternary structures of proteins or nucleic acids resulting in a loss of *bioactivity*.

*Note 1*: Modified from the definition given in ref.[1]

*Note 2*: Denaturation can occur when proteins and nucleic acids are subjected to elevated temperature or to extremes of pH, or to nonphysiological concentrations of salt, organic solvents, urea, or other chemical agents.

*Note 3*: An *[enzyme](/source/Enzyme)* loses its ability to alter or speed up a chemical reaction when it is denaturized.[2]

In [biochemistry](/source/Biochemistry), **denaturation** is a process in which [proteins](/source/Protein) or [nucleic acids](/source/Nucleic_acid) lose the [folded structure](/source/Protein_structure) present in their [native state](/source/Native_state) due to various factors, including application of some external stress or compound, such as a strong [acid](/source/Acid) or [base](/source/Base_(chemistry)), a concentrated [inorganic](/source/Inorganic) salt, an [organic](/source/Organic_compound) solvent (e.g., [alcohol](/source/Alcohol_(chemistry)) or [chloroform](/source/Chloroform)), agitation, radiation, or [heat](/source/Heat).[3] If proteins in a living [cell](/source/Cell_(biology)) are denatured, this results in disruption of cell activity and possibly [cell death](/source/Apoptosis). Protein denaturation is also a consequence of cell death.[4][5] Denatured proteins can exhibit a wide range of characteristics, from [conformational change](/source/Conformational_change) and loss of [solubility](/source/Solubility) or dissociation of [cofactors](/source/Cofactor_(biochemistry)) to [aggregation](/source/Protein_aggregation) due to the exposure of [hydrophobic](/source/Hydrophobic) groups. The loss of solubility as a result of denaturation is called [*coagulation*](/source/Precipitation_(chemistry)).[6] When denatured, proteins, e.g., [metalloenzymes](/source/Metalloenzyme), lose their [3D structure](/source/Protein_structure) or metal cofactor and, therefore, cannot function.

Proper [protein folding](/source/Protein_folding) is key to whether a [globular](/source/Globular_protein) or [membrane protein](/source/Membrane_protein) can do its job correctly; it must be folded into the native shape to function. However, [hydrogen bonds](/source/Hydrogen_bond) and cofactor-protein binding, which play a crucial role in folding, are rather weak, and thus, easily affected by heat, acidity, varying salt concentrations, [chelating agents](/source/Chelation), and other stressors which can denature the protein. This is one reason why cellular [homeostasis](/source/Homeostasis) is [physiologically](/source/Physiology) necessary in most [life forms](/source/Life).

## Common examples

When food is cooked, some of its proteins become denatured. This is why boiled eggs become hard and cooked meat becomes firm.

A classic example of denaturing in proteins comes from egg whites, which are typically largely [egg albumins](/source/Ovalbumin) in water. Fresh from the eggs, egg whites are transparent and liquid. Cooking the [thermally unstable](/source/Thermostability) whites turns them opaque, forming an interconnected solid mass.[7] The same transformation can be effected with a denaturing chemical. Pouring egg whites into a beaker of [acetone](/source/Acetone) will also turn egg whites [translucent](/source/Translucent) and solid. The skin that forms on [curdled](/source/Curdled) milk is another common example of denatured protein. The cold appetizer known as [ceviche](/source/Ceviche) is prepared by chemically "cooking" raw fish and shellfish in an acidic citrus marinade, without heat.[8]

## Protein denaturation

See also: [Equilibrium unfolding](/source/Equilibrium_unfolding)

Denatured proteins can exhibit a wide range of characteristics, from loss of [solubility](/source/Solubility) to [protein aggregation](/source/Protein_aggregation).

Process of denaturation:

1. Functional protein showing a quaternary structure
1. When heat is applied it alters the intramolecular bonds of the protein
1. Unfolding of the polypeptides (amino acids)

### Background

[Proteins](/source/Protein) or [polypeptides](/source/Polypeptide) are polymers of [amino acids](/source/Amino_acid). A protein is created by [ribosomes](/source/Ribosome) that "read" RNA that is encoded by [codons](/source/Codon) in the gene and assemble the requisite amino acid combination from the [genetic](/source/DNA) instruction, in a process known as [translation](/source/Translation_(genetics)). The newly created protein strand then undergoes [posttranslational modification](/source/Posttranslational_modification), in which additional [atoms](/source/Atom) or [molecules](/source/Molecule) are added, for example [copper](/source/Copper), [zinc](/source/Zinc), or [iron](/source/Iron). Once this post-translational modification process has been completed, the protein begins to fold (sometimes spontaneously and sometimes with [enzymatic](/source/Enzymatic) assistance), curling up on itself so that [hydrophobic](/source/Hydrophobic) elements of the protein are buried deep inside the structure and [hydrophilic](/source/Hydrophilic) elements end up on the outside. The final shape of a protein determines how it interacts with its environment.

Protein folding consists of a balance between a substantial amount of weak intra-molecular interactions within a protein (Hydrophobic, [electrostatic](/source/Electrostatics), and Van Der Waals Interactions) and protein-solvent interactions.[9] As a result, this process is heavily reliant on environmental state that the protein resides in.[9] These environmental conditions include, and are not limited to, [temperature](/source/Temperature), [salinity](/source/Salinity), [pressure](/source/Pressure), and the solvents that happen to be involved.[9] Consequently, any exposure to extreme stresses (e.g. heat or radiation, high inorganic salt concentrations, strong acids and bases) can disrupt a protein's interaction and inevitably lead to denaturation.[10]

When a protein is denatured, secondary and tertiary structures are altered but the [peptide bonds](/source/Peptide_bond) of the primary structure between the amino acids are left intact. Since all structural levels of the protein determine its function, the protein can no longer perform its function once it has been denatured. This is in contrast to [intrinsically unstructured proteins](/source/Intrinsically_unstructured_proteins), which are unfolded in their [native state](/source/Native_state), but still functionally active and tend to fold upon binding to their biological target.[11]

Shifts in normal pH range result in denaturation of enzymes. Decreasing the pH results in interactions between protons and amino acids, resulting in the breakage of existing hydrogen bonds.

### How denaturation occurs at levels of protein structure

See also: [Protein structure](/source/Protein_structure)

- In **quaternary structure** denaturation, protein sub-units are dissociated and/or the spatial arrangement of protein subunits is disrupted.

- **Tertiary structure** denaturation involves the disruption of: - [Covalent](/source/Covalent) interactions between amino acid [side-chains](/source/Side_chain) (such as [disulfide bridges](/source/Disulfide_bridge) between [cysteine](/source/Cysteine) groups) - Non-covalent [dipole](/source/Dipole)-dipole interactions between polar amino acid side-chains (and the surrounding [solvent](/source/Solvent)) - [Van der Waals (induced dipole) interactions](/source/Van_der_Waals_force) between nonpolar amino acid side-chains.

- In **secondary structure** denaturation, proteins lose all regular repeating patterns such as [alpha-helices](/source/Alpha_helix) and [beta-pleated sheets](/source/Beta_sheet), and adopt a [random coil](/source/Random_coil) configuration.

- **[Primary structure](/source/Protein_primary_structure)**, such as the sequence of amino acids held together by covalent peptide bonds, is not disrupted by denaturation.[12]

#### Loss of function

In a normal reaction, the substrate is able to bind to the active site to create the enzyme substrate complex, ultimately catalyzing a reaction. A denatured enzyme changes the shape of the active site, which prevents the substrate from binding to the enzyme active site. The enzyme is unable to perform its function, therefore **loss of function**.

Most biological substrates lose their biological function when denatured. For example, [enzymes](/source/Enzyme) lose their [activity](/source/Catalysis), because the substrates can no longer bind to the [active site](/source/Active_site),[13] and because amino acid residues involved in stabilizing substrates' [transition states](/source/Transition_state) are no longer positioned to be able to do so. The denaturing process and the associated loss of activity can be measured using techniques such as [dual-polarization interferometry](/source/Dual-polarization_interferometry), [CD](/source/Circular_dichroism), [QCM-D](/source/Quartz_crystal_microbalance_with_dissipation_monitoring) and [MP-SPR](/source/Multi-parametric_surface_plasmon_resonance).

#### Loss of activity due to heavy metals and metalloids

By targeting proteins, heavy metals have been known to disrupt the function and activity carried out by proteins.[14] Heavy metals fall into categories consisting of transition metals as well as a select amount of [metalloid](/source/Metalloid).[14] These metals, when interacting with native, folded proteins, tend to play a role in obstructing their biological activity.[14] This interference can be carried out in a different number of ways. These heavy metals can form a complex with the functional side chain groups present in a protein or form bonds to free thiols.[14] Heavy metals also play a role in oxidizing amino acid side chains present in protein.[14] Along with this, when interacting with metalloproteins, heavy metals can dislocate and replace key metal ions.[14] As a result, heavy metals can interfere with folded proteins, which can strongly deter protein stability and activity.

#### Reversibility and irreversibility

In many cases, denaturation is reversible (the proteins can regain their native state when the denaturing influence is removed). This process can be called **renaturation**.[15] This understanding has led to the notion that all the information needed for proteins to assume their native state was encoded in the primary structure of the protein, and hence in the [DNA](/source/DNA) that codes for the protein, the so-called "[Anfinsen's](/source/Christian_B._Anfinsen) [thermodynamic hypothesis](/source/Anfinsen's_dogma)".[16]

Denaturation can also be irreversible. This irreversibility is typically a kinetic, not thermodynamic irreversibility, as a folded protein generally has lower free energy than when it is unfolded. Through kinetic irreversibility, the fact that the protein is stuck in a local minimum can stop it from ever refolding after it has been irreversibly denatured.[17]

#### Protein denaturation due to pH

The enzyme depicted has an optimal pH of 8.3, so its [reaction rate](/source/Reaction_rate) is the highest at this pH. **Significantly increasing or decreasing** this reaction's pH can cause this enzyme to denature and, subsequently, decrease the reaction rate.

Denaturation can also be caused by changes in the pH which can affect the chemistry of the amino acids and their residues. The ionizable groups in amino acids are able to become ionized when changes in pH occur. A pH change to more acidic or more basic conditions can induce unfolding.[18] Acid-induced unfolding often occurs between pH 2 and 5, base-induced unfolding usually requires pH 10 or higher.[18]

## Consequences

### Loss of solubility

When proteins are folded, they fold so as to keep their [hydrophobic](/source/Hydrophobe) parts on the inside (away from water) and their [hydrophilic](/source/Hydrophilic) parts on the outside (contacting the water). This makes them soluble enough not to precipitate. However, when denatured the surface of the protein is partly hydrophobic and partly hydrophilic (as it no longer has an "inside" in which to hide the hydrophobic parts), causing it to become insoluble in water. The hydrophobic parts of the denatured proteins stick together, forming a network ([gel](/source/Gel)): this is called *coagulation*.[19]

The coagulation of denatured proteins is the reason [eggs solidify when cooked](/source/Eggs_as_food).[19] When acid is added to milk, the protein [casein](/source/Casein) denatures and coagulates (with fat and water inclusions from the milk) into [curds](/source/Curds), the first step in making [cheese](/source/Cheese);[19] although milk can also be made to curdle (i.e. casein to coagulate) by other methods, for example the addition of enzymes like [chymosin](/source/Chymosin).[20]

## Nucleic acid denaturation

Main article: [Nucleic acid thermodynamics](/source/Nucleic_acid_thermodynamics)

[Nucleic acids](/source/Nucleic_acid) (including [RNA](/source/RNA) and [DNA](/source/DNA)) are [nucleotide](/source/Nucleotide) polymers synthesized by [polymerase enzymes](/source/Polymerase) during either [transcription](/source/Transcription_(genetics)) or [DNA replication](/source/DNA_replication). Following 5'-3' synthesis of the backbone, individual [nitrogenous bases](/source/Nucleobase) are capable of interacting with one another via [hydrogen bonding](/source/Hydrogen_bond), thus allowing for the formation of higher-order structures. Nucleic acid denaturation occurs when hydrogen bonding between nucleotides is disrupted, and results in the separation of previously [annealed](/source/Annealing_(biology)) strands. For example, denaturation of DNA due to high temperatures results in the disruption of [base pairs](/source/Base_pair) and the separation of the double stranded helix into two single strands. Nucleic acid strands are capable of re-annealling when "[normal](/source/Polymerase_chain_reaction)" conditions are restored, but if restoration occurs too quickly, the nucleic acid strands may re-anneal imperfectly resulting in the improper pairing of bases.

### Biologically-induced denaturation

DNA denaturation occurs when hydrogen bonds between base pairs are disturbed.

The [non-covalent interactions](/source/Non-covalent_interactions) between [antiparallel strands](/source/Antiparallel_(biochemistry)) in DNA can be broken in order to "open" the [double helix](/source/Nucleic_acid_double_helix) when biologically important mechanisms such as DNA replication, transcription, [DNA repair](/source/DNA_repair) or protein binding are set to occur.[21] The area of partially separated DNA is known as the denaturation bubble, which can be more specifically defined as the opening of a DNA double helix through the coordinated separation of base pairs.[21]

The first model that attempted to describe the [thermodynamics](/source/Nucleic_acid_thermodynamics) of the denaturation bubble was introduced in 1966 and called the Poland-Scheraga Model. This model describes the denaturation of DNA strands as a function of [temperature](/source/Temperature). As the temperature increases, the hydrogen bonds between the base pairs are increasingly disturbed and "denatured loops" begin to form.[22] However, the Poland-Scheraga Model is now considered elementary because it fails to account for the confounding implications of [DNA sequence](/source/Nucleic_acid_sequence), chemical composition, [stiffness](/source/Stiffness) and [torsion](/source/Torsion_(mechanics)).[23]

Recent thermodynamic studies have inferred that the lifetime of a singular denaturation bubble ranges from 1 microsecond to 1 millisecond.[24] This information is based on established timescales of DNA replication and transcription.[24] Currently,[*[when?](https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Dates_and_numbers#Chronological_items)*] biophysical and biochemical research studies are being performed to more fully elucidate the thermodynamic details of the denaturation bubble.[24]

### Denaturation due to chemical agents

Formamide denatures DNA by disrupting the hydrogen bonds between base pairs. Orange, blue, green, and purple lines represent adenine, thymine, guanine, and cytosine respectively. The three short black lines between the bases and the formamide molecules represent newly formed hydrogen bonds.

With [polymerase chain reaction](/source/Polymerase_chain_reaction) (PCR) being among the most popular contexts in which DNA denaturation is desired, heating is the most frequent method of denaturation.[25] Other than denaturation by heat, nucleic acids can undergo the denaturation process through various chemical agents such as [formamide](/source/Formamide), [guanidine](/source/Guanidine), [sodium salicylate](/source/Sodium_salicylate), [dimethyl sulfoxide](/source/Dimethyl_sulfoxide) (DMSO), [propylene glycol](/source/Propylene_glycol), and [urea](/source/Urea).[26] These chemical denaturing agents lower the melting temperature (Tm) by competing for hydrogen bond donors and acceptors with pre-existing [nitrogenous base](/source/Nitrogenous_base) pairs. Some agents are even able to induce denaturation at room temperature. For example, [alkaline](/source/Alkalinity) agents (e.g. NaOH) have been shown to denature DNA by changing [pH](/source/PH) and removing hydrogen-bond contributing protons.[25] These denaturants have been employed to make [Denaturing Gradient Gel Electrophoresis gel](/source/Temperature_gradient_gel_electrophoresis) (DGGE), which promotes denaturation of nucleic acids in order to eliminate the influence of nucleic acid shape on their [electrophoretic](/source/Gel_electrophoresis_of_nucleic_acids) mobility.[27]

#### Chemical denaturation as an alternative

The [optical activity](/source/Optical_rotation) (absorption and scattering of light) and hydrodynamic properties ([translational diffusion](/source/Rotational_diffusion), [sedimentation coefficients](/source/Sedimentation_coefficient), and [rotational correlation times](/source/Rotational_correlation_time)) of [formamide](/source/Formamide) denatured nucleic acids are similar to those of heat-denatured nucleic acids.[26][28][29] Therefore, depending on the desired effect, chemically denaturing DNA can provide a gentler procedure for denaturing nucleic acids than denaturation induced by heat. Studies comparing different denaturation methods such as heating, beads mill of different bead sizes, probe [sonication](/source/Sonication), and chemical denaturation show that chemical denaturation can provide quicker denaturation compared to the other physical denaturation methods described.[25] Particularly in cases where rapid renaturation is desired, chemical denaturation agents can provide an ideal alternative to heating. For example, DNA strands denatured with [alkaline agents](/source/Alkalinity) such as [NaOH](/source/Sodium_hydroxide) renature as soon as [phosphate buffer](/source/Phosphate-buffered_saline) is added.[25]

#### Denaturation due to air

Small, [electronegative](/source/Electronegativity) molecules such as [nitrogen](/source/Nitrogen) and [oxygen](/source/Oxygen), which are the primary gases in [air](/source/Atmosphere_of_Earth), significantly impact the ability of surrounding molecules to participate in [hydrogen bonding](/source/Hydrogen_bond).[30] These molecules compete with surrounding hydrogen bond acceptors for hydrogen bond donors, therefore acting as "hydrogen bond breakers" and weakening interactions between surrounding molecules in the environment.[30] [Antiparellel strands](/source/Antiparallel_(biochemistry)) in DNA double helices are non-covalently bound by hydrogen bonding between base pairs;[31] nitrogen and oxygen therefore maintain the potential to weaken the integrity of DNA when exposed to air.[32] As a result, DNA strands exposed to air require less force to separate and exemplify lower [melting temperatures](/source/Nucleic_acid_thermodynamics).[32]

### Applications

Many laboratory techniques rely on the ability of nucleic acid strands to separate. By understanding the properties of nucleic acid denaturation, the following methods were created:

- [PCR](/source/Polymerase_chain_reaction)

- [Southern blot](/source/Southern_blot)

- [Northern blot](/source/Northern_blot)

- [DNA sequencing](/source/DNA_sequencing)

## Denaturants

### Protein denaturants

#### Acids

[Acidic](/source/Acid) protein denaturants include:

- [Acetic acid](/source/Acetic_acid)[33]

- [Trichloroacetic acid](/source/Trichloroacetic_acid) 12% in water

- [Sulfosalicylic acid](/source/Sulfosalicylic_acid)

#### Bases

[Bases](/source/Base_(chemistry)) work similarly to acids in denaturation. They include:

- [Sodium bicarbonate](/source/Sodium_bicarbonate)

#### Solvents

Most organic [solvents](/source/Solvent) are denaturing, including:[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [Ethanol](/source/Ethanol)

#### Cross-linking reagents

[Cross-linking](/source/Cross-link) agents for proteins include:[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [Formaldehyde](/source/Formaldehyde)

- [Glutaraldehyde](/source/Glutaraldehyde)

#### Chaotropic agents

[Chaotropic agents](/source/Chaotropic_agent) include:[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [Urea](/source/Urea) 6–8 [mol/L](/source/Molarity)

- [Guanidinium chloride](/source/Guanidinium_chloride) 6 mol/L

- [Lithium perchlorate](/source/Lithium_perchlorate) 4.5 mol/L

- [Sodium dodecyl sulfate](/source/Sodium_dodecyl_sulfate)

#### Disulfide bond reducers

Agents that break [disulfide bonds](/source/Disulfide_bond) by reduction include:[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [2-Mercaptoethanol](/source/2-Mercaptoethanol)

- [Dithiothreitol](/source/Dithiothreitol)

- [TCEP](/source/TCEP) (tris(2-carboxyethyl)phosphine)

#### Chemically reactive agents

Agents such as hydrogen peroxide, elemental chlorine, hypochlorous acid (chlorine water), bromine, bromine water, iodine, nitric and oxidising acids, and ozone react with sensitive moieties such as sulfide/thiol, activated aromatic rings (phenylalanine) in effect damage the protein and render it useless.

#### Other

- Mechanical agitation

- [Picric acid](/source/Picric_acid)

- Radiation

- Temperature[34]

- [Joule heating](/source/Joule_heating)

### Nucleic acid denaturants

#### Chemical

[Acidic](/source/Acid) nucleic acid denaturants include:

- [Acetic acid](/source/Acetic_acid)

- HCl

- Nitric acid

[Basic](/source/Acid) nucleic acid denaturants include:

- NaOH

Other nucleic acid denaturants include:

- [DMSO](/source/Dimethyl_sulfoxide)

- [Formamide](/source/Formamide)

- [Guanidine](/source/Guanidine)

- [Sodium salicylate](/source/Sodium_salicylate)

- [Propylene glycol](/source/Propylene_glycol)

- [Urea](/source/Urea)

#### Physical

- Thermal denaturation

- Beads mill

- Probe [sonication](/source/Sonication)

- [Radiation](/source/Radiation)

## See also

- [Denatured alcohol](/source/Denatured_alcohol)

- [Equilibrium unfolding](/source/Equilibrium_unfolding)

- [Fixation (histology)](/source/Fixation_(histology))

- [Molten globule](/source/Molten_globule)

- [Protein folding](/source/Protein_folding)

- [Random coil](/source/Random_coil)

## References

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1. ^ [***a***](#cite_ref-:01_9-0) [***b***](#cite_ref-:01_9-1) [***c***](#cite_ref-:01_9-2) Bondos, Sarah (2014). "Protein folding". *Access Science*. [doi](/source/Doi_(identifier)):[10.1036/1097-8542.801070](https://doi.org/10.1036%2F1097-8542.801070).

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1. ^ [***a***](#cite_ref-:02_25-0) [***b***](#cite_ref-:02_25-1) [***c***](#cite_ref-:02_25-2) [***d***](#cite_ref-:02_25-3) Wang, X (2014). ["Characterization of denaturation and renaturation of DNA for DNA hybridization"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4168728). *Environmental Health and Toxicology*. **29** e2014007. [doi](/source/Doi_(identifier)):[10.5620/eht.2014.29.e2014007](https://doi.org/10.5620%2Feht.2014.29.e2014007). [PMC](/source/PMC_(identifier)) [4168728](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4168728). [PMID](/source/PMID_(identifier)) [25234413](https://pubmed.ncbi.nlm.nih.gov/25234413).

1. ^ [***a***](#cite_ref-ReferenceA_26-0) [***b***](#cite_ref-ReferenceA_26-1) Marmur, J (1961). "Denaturation of deoxyribonucleic acid by formamide". *Biochimica et Biophysica Acta*. **51** (1): 91013–7. [doi](/source/Doi_(identifier)):[10.1016/0006-3002(61)91013-7](https://doi.org/10.1016%2F0006-3002%2861%2991013-7). [PMID](/source/PMID_(identifier)) [13767022](https://pubmed.ncbi.nlm.nih.gov/13767022).

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1. **[^](#cite_ref-33)** López-Alonso JP, Bruix M, Font J, Ribó M, Vilanova M, Jiménez MA, Santoro J, González C, Laurents DV (2010), ["NMR spectroscopy reveals that RNase A is chiefly denatured in 40% acetic acid: implications for oligomer formation by 3D domain swapping"](https://figshare.com/articles/NMR_Spectroscopy_Reveals_that_RNase_A_is_Chiefly_Denatured_in_40_Acetic_Acid_Implications_for_Oligomer_Formation_by_3D_Domain_Swapping/2792884), *J. Am. Chem. Soc.*, **132** (5): 1621–30, [Bibcode](/source/Bibcode_(identifier)):[2010JAChS.132.1621L](https://ui.adsabs.harvard.edu/abs/2010JAChS.132.1621L), [doi](/source/Doi_(identifier)):[10.1021/ja9081638](https://doi.org/10.1021%2Fja9081638), [PMID](/source/PMID_(identifier)) [20085318](https://pubmed.ncbi.nlm.nih.gov/20085318)

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## External links

- [McGraw-Hill Online Learning Center — Animation: Protein Denaturation](http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter2/animation__protein_denaturation.html)

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Adapted from the Wikipedia article [Denaturation (biochemistry)](https://en.wikipedia.org/wiki/Denaturation_(biochemistry)) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Denaturation_(biochemistry)?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.