VERFAHREN ZUR HERSTELLUNG EINES INSULINVORLÄUFERS

An insulin precursor of the formula I in which R1 = H, an amino-acid or peptide residue which can be eliminated chemically or enzymatically, R2 = OH or an amino-acid or peptide residue, X = a radical joining the insulin A and B chain, Y = residue of a genetically encodable amino acid, Z = residue of a genetically encodable amino acid, A1-A20 and B1-B29 = insulin peptide sequences which are non-mutated or mutated by exchange of one or more amino acids, is prepared by reacting a precursor in which the disulphide bridges between positions A6 and A11, A7 and B7, and A20 and B19, have not yet been formed, with excess mercaptan in the presence of an organic redox system or at least one organic compound which forms such an organic redox system under the reaction conditions. The particularly preferred organic redox system is the pair of compounds ascorbic acid + dehydroascorbic acid. The insulin precursor of the formula I can be converted into insulin either enzymatically or chemically by known techniques.