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.
Because of their
giant size, proteins exhibit colloidal properties such as low diffusion and
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.