[The purity of commercial insulin preparations]

Insulin preparations available in Germany were tested by polyacrylamide-disc electrophoresis. A large proportion of preparations contained proteins additional to insulin. Insulin purified chromatographically was cleaner than that by crystallization. Insulin purified by ion-exchange chromatography had the highest degree of purity: in addition to the insulin band only deamidation products of insulin were demonstrated. Deamidation occurs both in neutral and acid solvents. These observations indicate that commercial full purification of insulin is possible but not always practised.