By treating crystalline insulin at about 0°C. with acetic anhydride, an acetyl insulin is obtained, the activity of which is about one-fifth (8 units per milligram) of that of the original product.
By hydrolyzing the acetyl insulin with n/100 sodium hydroxide a product is obtained, the activity of which is about three times higher than that of the acetylated product, but which only shows half (25 units per milligram) of the activity of the original insulin.
The length of time that the acetylated insulin has to remain in contact with n/100 sodium hydroxide solution seems of no great importance in obtaining complete hydrolysis. The sulphur in acetyl insulin is more labile than in insulin.