Abstract: Methods for the selective conjugation of peptides which comprises an enzymatic incorporation of a functional group at the C-terminal end of a peptide followed by reaction with a second compound comprising the moiety to be conjugated to the peptide, wherein said second compound comprises a functional group which selectively reacts with the incorporated functional group.

Abstract: Human insulin precursors containing the peptide chain B(1-29)-A(1-21) of human insulin and derivatives thereof with a bridging chain connecting the carboxyl terminus of the B(1-29)-chain with the amino terminus of the A(1-21)-chain are prepared by culturing a yeast host transformed with a replicable expression vehicle capable of expressing a DNA-sequence encoding the insulin precursor. The bridging chain is preferably relatively short and contains preferably from 2 to 8 amino acid residues. The bridging chain must not contain two adjacent basic amino acid residues (Lys or Arg) and has one Lys or Arg connected to the amino terminus of the A(1-21)-chain. Human insulin is prepared from the insulin precursors by in vitro conversion.