Crystalline Insulin 



JOHN J. ABEL, M.D. 



In two preceding communications^- ^ it has been told how my col- 

 laborators and I were induced to attack the problem of the isolation 

 of insulin and what progress had been made toward 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 serviceable insulin ex- 

 tracts of commerce are boiled for a short time with N/IO sodium 

 carbonate the resulting physiological inactivation of the extracts is 

 always associated with an alteration of a part of their sulphur, an ele- 

 ment which our experiments justified us in believing to be an integral 

 constituent of the hormone itself. After such treatment ^vith a weak 

 alkali a new property appears in the altered insulin in that it now 

 shows an extraordinary sensitivity to very dilute acids which immedi- 

 ately, 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 sulphur of a preparation 

 is directly proportional to its hypoglycaemic activity for experimental 

 animals. In other words, the higher the amount of labile sulphur in a 

 given preparation the greater its potency in lowering the percentage 

 of blood sugar. 



The methods usually employed in fractioning and purifying bio- 

 logical mixtures have been found to be quite useless in the attempt 

 to separate the hormone from the numerous impurities that are asso- 

 ciated with it in even the best of the extracts employed in medical 

 practice. Equally unsuitable to the purpose in mind was the employ- 

 ment of the method of isoelectric precipitation from pH 4.7 to 5.0 no 

 matter how frequently repeated, as likewise the analogous method of 

 electro-dialysis— a method which has not yielded results of any particu- 

 lar value in the hands of those who have tried it out on insulin ex- 

 tracts. We are here dealing with an ampholyte present in very small 



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