title: C-terminal sequence determination of modified peptides by MALDI MS.
abstract: Peptides, cleaved by a mixture of carboxypeptidases CPP and CPY, can be detected by MALDI MS and the amino acid sequence thereby determined by calculation of the differences between consecutive peaks. In the present study we have used derivatizations of Lys and Cys to facilitate identification of these residues. Since the mass values do not readily distinguish Lys from Gln, we have converted Lys to homoarginine by guanidination, allowing simple detection of Lys. To identify the Cys positions in peptides that contain cystine, cysteic acid, or carboxymethylcysteine is not possible using CPY and CPP because of the lack of proteolytic cleavage. Instead we find that identification of Cys residues within the sequence can be achieved after conversion to a basic derivative, 4-thialaminine (Thi), by trimethylaminoethylation.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: V
authors.initials: V
authors.lastname: Bonetto
authors.forename: A C
authors.initials: AC
authors.lastname: Bergman
authors.forename: H
authors.initials: H
authors.lastname: Jörnvall
authors.forename: R
authors.initials: R
authors.lastname: Sillard
mesh_terms: D000595:Amino Acid Sequence; D002268:Carboxypeptidases / Q000378:metabolism; D043402:Cathepsin A; D003545:Cysteine / Q000032:analysis; D005973:Glutamine / Q000032:analysis; D008239:Lysine / Q000032:analysis; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D014660:Vasoactive Intestinal Peptide / Q000032:analysis
chemical_list: C069343:PEC-60 polypeptide; D010455:Peptides; D005973:Glutamine; D014660:Vasoactive Intestinal Peptide; C025427:carboxypeptidase P; D002268:Carboxypeptidases; D043402:Cathepsin A; D008239:Lysine; D003545:Cysteine