Industrial insulin production uses genetically engineered E. coli expressing a proinsulin gene controlled by a tryptophan promoter and containing a methionine linker for later cleavage. The cells also carry ampicillin resistance for selective growth. Seed cultures are stored at −80 °C and production begins by thawing a small amount to inoculate starter cultures, which are progressively scaled to a 50,000-L bioreactor. In the bioreactor, E. coli grow in nutrient-rich media under sterile, tightly regulated conditions: 37 °C, pH 7, ~30% air saturation, and controlled nutrient feeding. Proinsulin expression is initially repressed; induction with a chemical activator triggers the promoter, causing proinsulin to accumulate as insoluble cytoplasmic inclusion bodies. After fermentation, cells are harvested by centrifugation and lysed to release intracellular contents. Inclusion bodies are isolated by further centrifugation, washed to remove contaminants, and solubilized using strong denaturants such as urea or guanidine hydrochloride with reducing agents (e.g., DTT, β-mercaptoethanol). To prevent improper disulfide bond formation, the solubilized proinsulin undergoes oxidative sulfitolysis with sodium sulfite and sodium tetrathionate, stabilizing cysteine residues. This reaction is optimized at pH 9.5–11 and 25–37 °C, typically completing within 40 minutes. Excess reagents are removed via buffer exchange or desalting, and the protein is refolded by dilution or dialysis under oxidative conditions to restore correct disulfide pairing and native structure. Refolded proinsulin is enzymatically processed with trypsin and carboxypeptidase B to remove the C-peptide, generating active human insulin. Purification uses ion-exchange, size-exclusion, and reverse-phase chromatography to achieve pharmaceutical-grade purity. Finally, insulin is crystallized with zinc for stability, dried to powder, and formulated into injectable products such as vials, cartridges, or pens for global distribution.
Production of pharmaceutical proteins includes insulin, one of the most widely produced recombinant pharmaceutical proteins. One common production method uses genetically engineered E. coli to express human proinsulin.
Insulin production begins by inoculating starter flasks with E. coli seed culture. After incubation, the culture is scaled up into a large fed-batch bioreactor.
During the growth phase, proinsulin production remains repressed. Once the cells reach an optimal density, a chemical inducer is added to initiate proinsulin production.
This proinsulin accumulates in cells as inclusion bodies.
The cells are harvested and lysed to release the inclusion bodies, which are then solubilized to release unfolded proinsulin into solution.
Exposed cysteine residues in the proinsulin are temporarily blocked using sodium sulfite and tetrathionate to prevent incorrect disulfide bond formation.
Following removal of these reagents, the proinsulin is refolded under controlled conditions that favor correct disulfide bonding and restore native structure.
Finally, the proinsulin is enzymatically cleaved to yield mature insulin.
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