Recognizing single amino acid polymorphism in proteins

This paper describes a heavy isotope coding method that is used to identify single amino acid polymorphism of proteins. The method exploits differential derivatization of amine and carboxyl groups generated during proteolysis as a means of coding. After differentially double labeling samples, all the peptides having the same sequence in the control and experimental samples appear as a doublet in mass spectra. Uniquely different peptides coming only from one protein will appear as a singlet in mass spectra. The source of the singlet can be identified according to the special isotope pattern of O-18-labeled peptides. The amino acid sequence of the singlet can be determined using tandem mass spectrometry. This method was found to be of utility in detecting single amino acid polymorphism in proteins. The polymorphic portion of a protein can be identified without sequencing the whole protein. Six amino acid variations were recognized among the variations at seven sites between chicken and turkey lysozymes. Dog serum albumin from four breeds was also compared. Amino acid variations were identified at positions 359 and 474.