Properties of proteins
a. Generally proteins are colourless and tasteless. However, there are exceptions for example Hemoglobin is red in colour.
b. The solubility of proteins is influenced by pH. Proteins are least soluble at their iso electric point.
c. All protein solutions are optically active. The magnitude of optical activity depends on temperature, the wave length of light used and the concentration of protein.
d. Since proteins are macro molecules, their sizes are quantitatively expressed in terms of their molecular weights with kilo Daltons as their unit (kDa). For example the human serum albumin has a molecular weight of 66 kDa.
e. Because of their giant size, proteins exhibit colloidal properties such as low diffusion and Tyndall effect.
f. Proteins undergo hydrolysis upon treatment with concentrated mineral acids like HCl and yield constituent amino acids as their hydrochlorides. Similarly, proteolytic enzymes like trypsin and chymotrypsin hydrolyse proteins.
g. When proteins are treated with alkaline copper sulphate solution (Biuret reagent) they form a violet coloured complex called Biuret complex. This reaction can be used as a qualitative and quantitative test for proteins.