METHOD FOR DETERMINING ISOTOPIC CLUSTERS AND MONOISOTOPIC MASSES OF POLYPEPTIDES ON MASS SPECTRA OF COMPLEX POLYPEPTIDE MIXTURES AND COMPUTER-READABLE MEDIUM THEREOF

摘要

Disclosed herein is a method of finding an isotopic cluster in a polypeptide and determining the monoisotopic mass of the cluster. The method comprises an algorithm for finding an isotopic cluster based on a probabilistic model, defined by each of peaks in the isotopic cluster, and determining the monoisotopic mass of the isotopic cluster. The probabilistic model of the isotopic cluster includes characteristic functions for mass, that is, a function of the ratio of two peak intensities, and a function of the product of two ratios obtained from three peaks. These characteristic functions for mass define the shape of peaks acceptable in an actual isotopic cluster for the mass of any isotopic cluster. The algorithm of finding the isotopic cluster based on the functions uses the characteristics to score the degree of the approximation of any isotopic cluster to the spectral shape of a theoretical cluster. First, peaks that can be included in the same isotopic cluster at a distance of 1 Da are found, and then the score is calculated in consideration of, whether the ratio and the product of ratios of peak intensities falls in the range of the previously defined maximum and minimum values of the characteristic functions, and the similarity to the average value. Accordingly, each of isotopic clusters can be determined, and finally, isotopic clusters having an overlapping peak are removed such that each peak is included only in one isotopic cluster, and the monoisotopic mass of each isotopic cluster is determined.