June 10, 1999
Question from Providence, Rhode Island, USA:
Why can't you keep insulin in the freezer and then let is thaw? Does the insulin molecule denature? What is the temperature range that is okay in order for the protein to remain active?
Regular short acting insulin is a solution of microcrystalline insulin in a phosphate buffer with added zinc and bacteriostatic. The manufacturer gives specific instructions that the product should not be frozen. If this happens, some of the insulin may come out of solution and not be redissolved on thawing: it is not denatured. The same is true of the more complex forms of long acting insulin. Insulins are stable for 28 days if kept between 36 and 86 degrees Fahrenheit.