Insulin aspart is a recombinant, biosynthetic, fast-acting insulin analogue. It has a single amino acid substitution at position B28 where proline is replaced with aspartic acid. This substitution decreases its propensity to form hexamers and gives it a higher rate of absorption following subcutaneous administration compared to native insulin. Insulin aspart is produced in a genetically modified strain of Saccharomyces cerevisiae and harvested from a bioreactor.