Physicochemical properties of protein

Biochemistry, Human Health 9th Edition, including proteins with amphoteric ionizing properties, Proteins have colloidal properties, Denaturation and renaturation of proteins, etc.

Edited at 2024-02-08 16:39:12

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Physicochemical properties of protein

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Physicochemical properties of protein

Proteins have zwitterionic properties

Isoelectric point of protein: When the protein solution is at pH, the protein has an equal tendency to dissociate into positive and negative ions, becoming zwitterionic ions with a net charge of zero. At this time, the pH of the solution is called the isoelectric point of the protein.

protein electrophoresis

Proteins are charged particles in solutions higher or lower than their pI and can move toward the positive or negative pole in an electric field. This technique of separating various proteins by swimming them in an electric field is called electrophoresis.

According to different supports, it can be divided into thin film electrophoresis and gel electrophoresis.

Several important protein electrophoresis: SDS-polypropylene gel electrophoresis, isoelectric focusing electrophoresis, two-dimensional electrophoresis

protein chromatography

Ion exchange chromatography: Separation using different charges and properties of proteins

Gel filtration, also known as molecular sieve chromatography

Proteins have colloidal properties

Factors that stabilize protein colloids

particle surface charge

hydration film

Most protein surfaces have hydrophilic groups that can attract water molecules and form a hydration film.

Dialysis and ultrafiltration

Proteins cannot pass through semipermeable membranes

Ultrafiltration requires pressurization

protein precipitation

Dehydration, removal of colloidal surface charge

method

Salting out Principle: Destroy the hydration film and neutralize the charge Protein remains active

Organic solvents Principle: Destroy the hydration membrane protein inactivation

Immunoprecipitation

Denaturation and renaturation of proteins

protein denaturation Under the action of certain physical and chemical factors, the specific spatial conformation of proteins is destroyed, that is, the ordered spatial structure becomes a disordered spatial structure, resulting in changes in its physical and chemical properties and loss of biological activity.

It is generally believed that protein denaturation mainly occurs through the destruction of disulfide bonds and non-covalent bonds, and does not involve changes in the amino acid sequence in the primary structure.

Protein renaturation If the degree of protein denaturation is minor, the protein can still recover or partially recover its original conformation and function after removing the denaturing factors.

protein precipitation Under certain conditions, when the hydrophobic side chains of proteins are exposed, the peptide chains will tangle with each other and then aggregate, thus precipitating from the solution.

Protein coagulation The deformed floc of the protein can be turned into a relatively solid clot when heated, and this clot is not easily redissolvable in strong acids and alkalis.

Proteins have characteristic light absorption in the ultraviolet spectral region

Since protein molecules contain conjugated double bonds of tyrosine and tryptophan, they have a characteristic absorption peak at a wavelength of 280nm.

color reaction of protein

Ninhydrin reaction

This reaction can also occur with amino acids produced after protein hydrolysis

biuret reaction

The peptide bonds in proteins and polypeptide molecules turn purple or red when heated with copper sulfate in a dilute alkaline solution.

As protein hydrolysis reduces peptide bonds, the color depth of biuret decreases.