Denaturation, reversible insulin

Organic solvents are often used in the manufacture, purification, precipitation and crystallization of protein pharmaceuticals (Sukumar et al., 2005). Water miscible solvents such as ethanol, acetonitrile and propanol have been utilized to promote the stabilization of reversible denaturation and aggregation, with recovery of the native conformation. For example, insulin has been precipitated and/or crystallized in a wide variety of solvents (Brange and Lanlqaer, 1993). 

The effects of alkali up to 0.1 N on the absorption spectrum of lysozyme are fully reversible, according to Fromageot and Schnek (1950) it is of interest to note that this enzyme is a protein which is remarkably resistant to denaturation (Fraenkel-Conrat, 1950). Insulin behaves similarly, and it may be surmised that in both these proteins the tyrosine hydroxyl groups are not bound. The pK value of 10.8 found by Fromageot and Schnek (1950) for lysozyme supports this view. The pK data for insulin are more complicated and have been discussed at length by Crammer and Neuberger (1943). 

---