Stability of bovine insulin.

A stability experiment on purified crystalline bovine insulin showed that it deteriorates at normal refrigeration temperature (5 degrees C) and that storage at -20 degrees C is necessary to ensure stability. Purified insulin degrades by two mechanisms: deamidation and polymerization. Immunochemical potency determinations alone are insufficient to determine the stability of insulin as they may be little affected by the chemical changes which occur on storage. The activation energy for the polymerization of insulin was found to be 66 kJ mol-1 and for deamidation 45 kJ mol-1. It is recommended that crystalline bovine insulin be stored at -20 degrees C.