Insulin is a hormone that regulates the amount of glucose in the blood and is required for the body to function normally. The gene that codes for the production of insulin is located in the short arm of chromosome 11. It has a total of 51 amino acids and 2 polypeptide chains called A and B. Insulin is produced by cells in the pancreas, called the islets of Langerhans. These cells continuously release a small amount of insulin into the body, but they release surges of the hormone in response to a rise in the blood glucose level.

Deficiency in the production of insulin or defects in its utilization lead to diabetes. In the past, porcine or bovine insulin was the main source of insulin for diabetics. However, the use of porcine or bovine insulin was associated with many drawbacks, the main one being that it is associated with immune reactions. Whereas both porcine and bovine insulin are similar to that of humans, the similarity is not 100%. Therefore, some patients produce antibodies against the porcine or bovine insulin since their bodies regard it as foreign and this may lead to complications. As a result, recombinant DNA technologies have largely replaced abattoir methods. Two methods are commonly used to produce recombinant human insulin. The first method involves the generation of an insulin precursor with the expression host being the E. coli bacteria. This is then followed by solubilization and refolding techniques. The second method involves the generation of insulin precursor (IP) using yeast expression systems. In this method, Saccharomyces cerevisiae and more recently Pichia pastoris are used as expression vectors.