Hydrolysis of polypeptides


Hydrolysis the breaking down of a substance using the elements of water. In the lab hydrolysis is usually carried out by heating the substance to be broken down to 100 0C with concentrated acid (H+) or concentrated alkali under reflux for several hours. Under acidic conditions a polypeptide or protein will be broken up into numerous amino acids that make up the polypeptide or protein. Obviously if the hydrolysis reaction is carried out in the presence of concentrated acid the carboxylate ion (-C02-) will be protonated as will the amine group present in the amino acid. This results in the formation of a cation. As a simple example the acid hydrolysis of the dipeptide formed from the amino acids alanine and glycine is shown below:

acid hydrolysis of a dipeptide

alkaline hydrolysis of a dipeptide molecule

Polypeptides and proteins can also be hydrolysed by heating them under reflux at 1000C with a concentrated alkali such as sodium hydroxide. This time the amino acids produced will react with the basic sodium hydroxide to form the sodium salt from the carboxyl group on the amino acid. This is outlined below where a dipeptide is hydrolysed.

Alkaline hydrolysis of a dipeptide molecule using sodium hydroxide solution

Key Points

Practice questions

Check your understanding - Questions on protein hydrolysis.