Abstract: The method for preparation of a recombinant protein from a precursor, preferably mammalian insulins, including human insulins and their analogues, characterised in that a protease is used which hydrolyses one or more peptide bonds in this protein, wherein the protease disrupts the peptide bond from the C-end side of a basic amino acid, when the amino acid is the second one after other basic or neutral amino acid, and such an order enables specific recognition of both amino acids by the protease. The invention is applicable in biotechnology and pharmaceutical industry.