Proteins give several colour reactions and are often useful in identifying the nature of amino acids.
All proteins rotate the plane-polarised light to the left; that is, these are laevorotatory. Example: Specific rotation [α]D for ovalbumin is near –30° over the pH range 3.5 × 11. However at lower or higher pH values the rotation becomes more negative eg at pH 13, the [α]D is about –60°.
The process of protein precipitation by the addition of neutral salts such as ammonium sulphate or sodium sulphate is known as salting out. This phenomenon is explained on the basis of dehydration of protein molecule by salts. This causes increased protein, protein interaction, resulting in molecular aggregation and precipitation.
The addition of small quantities of neutral salts increases the solubility of proteins. This process is called salting. Due to the diminished protein, protein interaction is at low salt concentration.
The solubility of proteins usually depends on the pH. It is lowest at the isoelectric point and increases with increasing alkalinity or acidity. The reason is that as protein molecules exist as either cations or anions, repulsive forces between the ions are high and hence the proteins possess excess charges of the same sign. Thus,…
As proteins are amphoteric in nature, they can form salts with both cations and anions. Many ions form insoluble salts with proteins and therefore they are used as precipitating agents for protein. Example: Anions of some acids like phosphotungstic, trichloroacetic acid, picric acid, and so on form insoluble acids with proteins. Heavy metals are used for…
Proteins are amphoteric in nature; that is, they have both acidic and basic properties. In the electric field, their migration depends upon the net charge carried by the molecule. The net charge is influenced by the pH value. Each protein has a specific pI value at which it will not move, because at this point…
Proteins exhibit colloidal properties. They show considerable light-scattering effect in solution and hence result in visible turbidity (Tyndall effect).
Proteins vary in their molecular weight, which, in turn, is dependent on the number of amino acid residues. Each amino acid on an average contributes to a molecular weight of about 110. Majority of protein polypeptides may be composed of 40 to 40,000 amino acids with a molecular weight ranging from 4,000 to 4, 40,000.…
Physical properties Colour and taste: Proteins are colourless and usually tasteless. These are homogenous and crystalline. Shape and size: Proteins range in shape from simple crystalloid spherical structure to long fibrillar structure.