Effective Fluorescent and -Iodine Labelling of Proteins with a New Labelling Reagent

A new fluorescent labelling reagent, which was previously devel oped for the labelling of polysaccharides, was also applied to the labelling of non-glycosilated proteins, aspartate aminotransferase and tumor necrosis factor-α. Both proteins were labelled over a range of fluorescent substitutions (0.2 to 1.6 fluorescent moieties per protein molecule) without loss of biological activity. The fluorescent reagent can also be initially labelled with ¹²⁵ -iodine. The specific radioactivity and biologic activity of labelled tumor necrosis factor-α were equivalent to that prepared by a conventional technique for radio iodination. It is demonstrated that this new derivative chemistry may be ap plicable to the non-destructive labelling of a wide range of proteins in addition to polysaccharides.