Amino Acid Composition Determination From the Fractional Mass of Peptides

A peptide's fractional mass is directly associated with its elemental composition and thus amino acid composition. Here it is demonstrated that a peptide's fractional mass alone can be a useful identifier or indicator of that composition for small to mid-sized peptides (5-7 amino acids) and can significantly reduce the number of viable amino acid compositions for larger peptides (> 8 residues) to include or exclude certain possibilities. Separate consideration of the integer portion of the peptide's mass helps to reduce the number of possibilities where many duplicate fractional mass values are found. Adoption of this fractional mass strategy should aid approaches that are presently employed for peptide identification, including in the use of mass map data to search protein databases for proteomics applications.