ACCURACY REQUIREMENTS FOR PEPTIDE CHARACTERIZATION BY MONOISOTOPIC MOLECULAR-MASS MEASUREMENTS

Accurately measured monoisotopic mass of a biomolecule can reveal its elemental and, in the case of a biopolymer, its monomer composition, I n this work, the limitations of the technique were analyzed in applica tion to peptides, For the currently available level of mass accuracy o f about +/-1 ppm, the mass limit for revealing the unique elemental co mposition of a peptide was found to be 700-800 Da, with the possibilit y to extend this range as the mass accuracy improves, As for the amino acid composition determination, the principal limit of similar to 500 -600 Da cannot be overcome in the general case by instrumental or meth odological improvements. It is proposed that, for the peptide characte rization, the molecular mass must be determined with sufficient accura cy to rule out a significant fraction of the peptides having the same nominal mass but different elemental and amino acid compositions, An a ccuracy of +/-1 ppm tvas found to exclude 99% of such peptides and, th erefore, ensure a high degree of confidence in peptide characterizatio n.