Structure of a soluble super-active insulin is revealed by the nature of the complex between cyanogen-bromide-activated sepharose and amines.

Insulin-like material with elevated insulin specific acitivity is released from insulin-Sepharose in the presence of bovine-serum albumin. The mechanism of release and the chemical nature of this insulin-like material are revealed by the finding that amine-Sepharose is O-Sepharose-N-substituted isourea. Nucleophilic attack by amino groups releases N-1-N-2-disubstituted guanidines. Correspondingly, it is shown that the super-active insulin-like material is an N-1-N-2-disubstituted guanidine in which insulin and bovine-serum albumin are the substituents.