Determination of Molecular Weights of Intact Proteins.
Mass spectra of intact protein fragments allow detection of precise molecular weights of major and minor proteins, although larger proteins, being heterogeneous, make determination of their precise molecular weights difficult. However, high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been used for accurate determination of masses of small intact proteins. But the molecular weight alone may not be enough for protein identification, and peptide sequencing by tandem mass spectrometery, as described above, may be needed.