Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometric analysis of the recombinant human macrophage colony stimulating factor beta and derivatives

The potential of electrospray ionization (ESI) Fourier transform ion cyclot ron mass spectrometry (FTICR-MS) to assist in the structural characterizati on of monomeric and dimeric derivatives of the macrophage colony stimulatin g factor beta (rhM-CSF beta) was assessed. Mass spectrometric analysis of t he 49 kDa protein required the use of sustained off-resonance irradiation ( SORT) in-trap cleanup to reduce adduction. High resolution mass spectra wer e acquired for a fully reduced and a fully S-cyanylated monomeric derivativ e (similar to 25 kDa). Mass accuracy for monomeric derivatives was better t han 5 ppm, after applying a new calibration method (i.e., DeCAL) which elim inates space charge effects upon high accuracy mass measurements. This high mass accuracy allowed the direct determination of the exact number of inco rporated cyanyl groups. Collisionally induced dissociation using SORI yield ed b- and y-fragment ions within the N- and C-terminal regions for the mono meric derivatives, but obtaining information on other regions required prot eolytic digestion, or potentially the use of alternative dissociation metho ds. (C) 2000 American Society for Mass Spectrometry.