Crystalline Insulin

Abstract

In two preceding communications [1, 2] it has been told how my collaboratprs and I were induced to attack the problem of the isolation of insulin and what progress has been made towards its solution to within a few months past. It was there pointed out that a clue had been found, the following out of which promised to lead to the desired goal. This clue eventuated from the observation that when the highly impure and complex, though therapeutically servicable insulin extracts of commerce are boiled for a short time with N/10 sodium carbonate the resulting physioloogical inactivation of the extracts is always associated with an alteration of a part of their sulphur, an element which our experiments justified us in believing to be an integral constituent of the hormone itself. After such treatment with a weak alkali a new property appears in the altered insulin in that it now shows an extraordinary sensitivity to very dilute acides which immediately, and contrary to their usual action, liberate hydrogen sulphide from it. It was found that inert fractions prepared from such extracts of the pancreas contain very little of this labile sulphur and a table was constructed which showed that the labile suplphur of a preparation is directly proportional to its hypoglycaemic activity for experimental animals. In other words, the higher amount of labile sulphur in a given preparation the greater its potency in lowering the percentage of blood sugar.