Humulin Production:
    Recombinant DNA used to produce human insulin


Ever since Banting and Best isolated a protein they called "isletin" from the Islets of Langerhans from a pancreas and injected it into diabetic dogs, insulin has been used to help diabetics live out their lives.  However, this protein had its problems.  For many years, insulin was extracted and purified from either porcine or bovine pancreases, and this carried with it two main difficulties.  The first was that though the animal insulin was chemically similar to human insulin, there were some differences, and these differences led to antibody attack and inactivation as well as inflammation in many patients.  Also, there was the problem that this method of extracting insulin from animal organs made it difficult to obtain large amounts of pure insulin.

Nowadays, it is a well known fact that DNA contains genes which encode all the different proteins that an organism can produce.  But back then, the composition of proteins and their relation to DNA was unknown.  It wasn't until Sanger, in 1955, determined the sequence of insulin and determined that proteins are composed of specific amino acids linked to each other in a peptide chain.  And even then, it wasn't until 1979 that human insulin was able to be produced in large quantities.  This was done by the use of recombinant DNA.

Recombinant DNA, or rDNA, is DNA which specifically encodes a protein.  This is cut from genomic DNA by a restriction enzyme which cuts DNA at specific sequences along the chain.  These pieces are then analyzed and the DNA needed to make the protein is extracted and purified.  Since insulin contains two polypeptide chains linked by disulfide bonds, two pieces of DNA are extracted.  These DNA strands are then placed into two different plasmids, as shown in the figure below.

These plasmids are also cut with the same restriction enzymes as the DNA,which will allow the DNA to be fixed into the plasmid by DNA ligase.  The plasmids are then incubated with a weakened strain of E. coli. Since only some of the bacteria will take up the plasmid,a gene encoding an enzyme which breaks down a certain antibiotic is also included in the plasmid, which allows bacteria with the plasmid to grow on a plate containing the antibiotic while the other bacteria die.  These bacteria are then allowed to grow and replicate, which allows the plasmid and the insulin gene to replicate millions of times.  Then the bacteria are given a signal to produce the protein, and insulin identical to that of humans can be produced and purified.  This insulin, which is abtly named humulin, can then be used to treat many people with type I diabetes without the worry of allergic reaction.

For more information on treatment of Diabetes I and II, click here.

For medications for Diabetes type II, click here.