Why is protein denatured by heat irreversible

Denatured proteins only have the destruction of spatial conformation, and it is generally believed that the essence of protein denaturation is secondary bonds, and the destruction of disulfide bonds does not involve changes in the primary structure.

The most obvious difference between denatured proteins and native proteins is the decrease in solubility, the increase in viscosity of proteins, the destruction of crystallinity, the loss of biological activity, and the susceptibility to protease decomposition.

Denaturation is not an irreversible change, when the degree of denaturation is mild, such as removing the denaturation factor, some proteins can still recover or partially restore their original conformation and function, and the reversible change of denaturation is called reversibility. For example, the aforementioned ribonuclease has four pairs of disulfide bonds and their hydrogen bonds. Under the action of mercaptoethanol and 8M urea, denaturation occurs, loss of biological activity, after denaturation, such as dialysis to remove urea, mercaptoethanol, and try to oxidize the phobic group into disulfide bonds, the enzyme protein can restore its original conformation, and the biological activity is almost all restored, which is called the renaturation of denatured ribonuclease.

Many proteins are severely damaged when denatured and cannot be recovered, which is called irreversible denaturation.

1. High temperature will denature proteins. Common such as boiled eggs, eggs from a liquid state to solid, is a process of protein inactivation and denaturation.

2. In addition to high temperatures, acidic and alkaline environments, as well as heavy metal salts and ultraviolet rays will denature proteins.

3. Proteins that have coagulated by chemical reactions with acids, alkalis, heavy metal salts and ultraviolet rays have changed their chemical structure and cannot be restored to their original state.

Because the spatial structure of the protein has not changed or has not changed much.

Under a certain strip of the piece, the protein precipitates, the slip and the spatial structure do not change, and the protein regains activity when the denaturation condition is removed. For example, salting out, in which the protein is denatured and precipitated in a high concentration of salt, but when an appropriate amount of water is added to reduce the concentration of the salt solution, the protein dissolves again and recovers its activity.

When the protein is subjected to light, heat, organic solvents and some denaturants, the secondary bonds are broken, resulting in the destruction of the natural conformation and the loss of the biological activity of the protein. If the denaturation conditions are vigorous and persistent, the denaturation of the protein is irreversible. If the denaturation conditions are not drastic, this denaturation is reversible, indicating that the internal structure of the protein molecule has not changed much.

In this case, if the denaturation factor is removed, the denatured protein can regain its native conformation and biological activity under the right conditions.

Protein denaturation is non-toxic.

The protein denaturation mentioned here generally occurs under conditions such as high temperature, excessive acidity or alkaline. Protein denaturation It refers to a change in the spatial structure of the protein, as opposed to the so-called food spoilage. That is to say, it can be understood that before the protein is not denatured, its structure is relatively tight, and the denaturation will make its structure loose, in other words, it can be thought of as a ball of hemp rope with dead knots before denaturation, and the so-called protein denaturation is to make these knots loose and easy to find a breakthrough.

For example, if we eat raw eggs, they may not be easy to digest, but when the eggs are boiled or denatured by other cooking methods, their loose structure becomes easier to digest.

Therefore the protein is denatured and it is not toxic.

1. The theory of protein denaturation was first proposed by Wu Xian in 1931, and he believed that the loss of activity of proteins was the result of changes in their conformation under specific factors. Denaturation differs from hydrolysis in that it does not involve changes in the primary structure of the protein (e.g., peptide bond breaking, fibrillation), but only the secondary bonds that maintain the higher order structure of the protein are severely disrupted.

2. The ways that can denature proteins are: high temperature, extreme low temperature, acid, alkali, heavy metal ions, organic solvents, formaldehyde, urea, high-intensity radiation, etc.

3. High temperature can denature the white matter and nucleic acid of microorganisms in food and kill microorganisms, so high temperature, such as heating eggs and meat, is a commonly used disinfection method. Medical alcohol can be sterilized for the same reason.