Insulin is a protein.
Proteins consist of sequences of amino acids.
Human insulin has the amino acid lysine at position B28 and proline at position B29. Switching the B28 and B29 positions on the protein has no effect on the normal activity of the insulin but inhibits the formation of the dimer and the hexamer. Thus the insulin is in monomeric form when injected and can be absorbed immediately. The name LysPro comes from the names of the amino acids, lysine and proline, that occupy the swapped positions. According to an article in the August 1996 Diabetes Forecast, the spelling 'lispro' is now preferred.