Note on the adsorption of insulin by kaolin.

Abstract

Considerable progress has been made in the purification of enzymes since Willstätter and his coworkers have perfected the method of adsorption and elution. 1 It occurred to us that these methods might be successfully used in the further purification of insulin. Quantitative studies of the behavior of insulin in adsorption are difficult owing to the necessity of assaying the insulin physiologically. This difficulty, we believe, may now be overcome by the use of the iodometric method of estimation. 2

This report deals with our studies on the adsorption of insulin by kaolin. The kaolin used in our experiments was a special brand, purified by electrodialysis. 3 The insulin preparation used (Lilly lot 769999, 20 units per mg.) contained 440 units per cc., and had an iodine value of 21.7 cc. 0.01 N iodine in neutral-buffered solution and of 34.5 cc. 0.01 N iodine in alakaline solution. The preservative was removed from the insulin preparation by isoelectric precipitation, because phenols interfere with the iodometric estimation. There were adsorbed 440 units of insulin on varying amounts of kaolin for 15 min. and centrifuged. The supernatant fluid is designated “adsorption rest-solution.” The table shows our results on adsorption and elution, the percentages of insulin recovered from the solutions corresponding to the different steps in the procedure, and the iodine values from which the percentages of insulin were calculated. The amount and potency of the insulin in the adsorption rest-solutions and in the precipitates from the elutions has been roughly assayed physiologically as a check for the iodometric estimations.