Selective biochemical modification of functional residues in recombinant human macrophage colony-stimulating factor beta (rhM-CSF beta): identification by mass spectrometry

A rapid procedure for identifying amino acids in the recombinant human macrophage colony-stimulating factor (rhM-CSF) protein of potential import to the ligand-receptor interaction, was developed. The method combines classical chemical modification with mass spectrometry. Diethyl pyrocarbonate modification of rhM-CSF results in a time- and concentration-dependent loss in receptor binding and biological activity. At low DEP:M-CSF ratios, there was selective modification of histidine residues, while at higher ratios, Tyr and Lys residues were also modified.