In detail, for example the following procedure is applied for this purpose: MIA-containing protein aggregates from E. coli fermentations (socalled inclusion bodies") are solubilized in 6M guanidinium hydrochloride, 100 mM TrisHCl at pH 8, 1 mM EDTA, subsequently adjusted to a pH of 3 to 4 and dialyzed against 4M guanidinium hydrochloride at pH 3.5.