1. Preproinsulin is a proinsulin molecule with a signal peptide attached to its N-terminus. 2. In the RER the proinsulin folds into the correct conformation and 3 disulfide bonds are formed. 3. -- Proinsulin is a precursor of insulin, which the body makes to convert sugar to energy. 4. The signal peptide is cleaved as the polypeptide is translocated into lumen of the RER, forming proinsulin . 5. When insulin was originally purified from bovine or porcine pancreata, all the proinsulin was not fully removed. 6. This can be described as an iatrogenic injury due to slight differences between the proinsulin of different species. 7. Proinsulin C-peptide was first described in 1967 in connection with the discovery of the insulin biosynthesis pathway.8. The signal sequence is cleaved from the N-terminus of the peptide by a signal peptidase, leaving proinsulin . 9. Insulin resistance in Type 2 diabetes produces a greater demand for insulin production which results in the secretion of proinsulin . 10. More modification can occur in the secretory vesicles ( for example insulin is cleaved from proinsulin in the secretory vesicles ).
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