EP 081:39

Insulin: one chain, cut in two

Name: Insulin: one chain, cut in two
Uploaded: 2026-09-28
Duration: 1 min 39 s
Description: The body makes insulin as one long chain and cuts out the middle. The story of the 1922 patient, the Nobel Prize, and why the FDA now calls insulin a protein.

The body makes insulin as one long chain and cuts out the middle. The story of the 1922 patient, the Nobel Prize, and why the FDA now calls insulin a protein.

Transcript and sources

In January nineteen twenty-two, a fourteen-year-old boy in Toronto got an injection of insulin. The first try did little. The second, with a purer extract, brought immediate improvement.
Insulin is a hormone made of fifty-one amino acids, in two chains: one of twenty-one, and one of thirty.
Three sulfur bridges hold the chains together: two link them, and one loops inside the short chain.
But the body doesn't make two chains. It makes one, called proinsulin, eighty-six amino acids long.
Then enzymes cut out a thirty-one-amino-acid middle piece, the C-peptide, and what's left is insulin.
In nineteen twenty-three, Banting and Macleod won the Nobel Prize for the discovery of insulin, and Banting, Best and Collip sold their patent to the University of Toronto for one dollar each.
In the nineteen fifties, Frederick Sanger worked out insulin's full sequence, the first protein ever mapped. He won a Nobel Prize for it in nineteen fifty-eight.
In nineteen eighty-two, the FDA approved Humulin, human insulin made by bacteria: the first approved medicine made with recombinant DNA.
Then, in twenty twenty, the FDA moved insulin from drugs to biologics. Why? U.S. rules call a chain longer than forty amino acids a protein, and insulin's two chains count together: fifty-one.
So by the FDA's own ruler, insulin is a protein, though the medicine itself hasn't changed. See where every peptide sits, at peplexicon.com.

Sources