Sequence analysis of peptides with biological activities using electrospray-Fourier transform ion cyclotron resonance mass spectrometry

(T) he mass spectra of five peptides with biological activities are reporte d. All mass spectra were recorded using a 4.7-T Fourier transform ion cyclo tron resonance mass spectrometer equipped with an external electrospray sou rce. The accurate molecular weights for the five peptides prepared by solid phase synthesis were measured as 1765.9013, 1063.5420, 1092.5254, 820.3804 and 1078.5193, respectively. All the data were obtained with the external calibration. Differences between observed and theoretical monoisotopic mole cular weights were in the (0.2-1.0)x10(-6) range. The complete primary sequ ence for the five polypeptides were determined using the method of in-sourc e electrospray ionization/collision induced dissociation (ESI/CID). All the intact y series ions and b series ions were obtained from various peptides respectively, thus determining the sequences of the five polypeptides. We found that the measured accurate molecular mass of sample 4 was not in agre ement with that expected from the planned synthetic peptide. The sequences of sample 4 were determined through analysis. The corresponding accurate ma sses of b series ions and y series ions were gained, which proved that it w as correct to re-determine the sequences.