Process for obtaining insulin having correctly linked cystine bridges

Claimed is a process for the isolation of correctly linked insulin by reacting (a) a protein of the formula R -R -B2-B29-Y-X-Gly-A2-A20-R (II) in which X = amino acids Lys or Arg or a peptide with 2 to 35 amino acids contg. Arg or Lys at the N-terminal and carboxyl end of the peptide Y = amino acid R = phenyl alanine residue or a covalent bond R = hydrogen, Arg or Lys, a peptide with 2 to 45 amino acids contg. Arg or Lys at the carboxyl end of the peptide, R = an amino acid residue, A2-A20 and B2 to B29 correspond to the amino acid sequence of the A or B chain respectively of human insulin, animal insulin or insulin derivs. with an mercaptan amt. resulting in 2 to 10 SH-residues of the mercaptan per cystein residue of formula (II) in the presence of a chaotropic auxiliary agent in an aq. medium at a pH of 10 to 11 and protein concns. of 0.05 and 0.3 g/l, (b) reacting the proinsulin obtd. including correctly linked cystine bridges with either trypsin, trypsin-like protein or opt. also with carboxypetidase B or a mixt. thereof for the prodn. of correctly folded insulin and (c) adding to the prod. of (b) 3 to 50 g of a hydrophobic absorber resin per litre of aq. medium at a pH of 4 to 7 and (d) isolating the absorber resin with absorbed insulin and e) eluting the insulin.