title: A method for the detection of asparagine deamidation and aspartate isomerization of proteins by MALDI/TOF-mass spectrometry using endoproteinase Asp-N.
abstract: A method was established for evaluating Asn deamidation and Asp isomerization/racemization. To detect the subtle changes in mass that accompany these chemical modifications, we used a combination of enzyme digestion by endoproteinase Asp-N, which selectively cleaves the N-terminus of L-alpha-Asp, and MALDI/TOF-mass spectrometry. To achieve better resolution, we employed digests of (15)N-labeled protein as an internal standard. To demonstrate the advantages of this method, we applied it to identify deamidated sites in mutant lysozymes in which the Asn residue is mutated to Asp. We also identified the deamidation or isomerization site of the lysozyme samples after incubating them under acidic or basic conditions.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyushu University, 3-3-1 Maidashi, Higashi-ku, Fukuoka 812-8582.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kameoka
authors.forename: Tadashi
authors.initials: T
authors.lastname: Ueda
authors.forename: Taiji
authors.initials: T
authors.lastname: Imoto
mesh_terms: D000577:Amides / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000737:chemistry* / Q000378:metabolism; D001224:Aspartic Acid / Q000737:chemistry* / Q000378:metabolism; D002645:Chickens; D003641:Deamination; D004529:Egg White; D010450:Endopeptidases / Q000378:metabolism*; D007536:Isomerism; D008666:Metalloendopeptidases; D008969:Molecular Sequence Data; D009113:Muramidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009587:Nitrogen Isotopes; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020539:Sequence Analysis, Protein / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D000577:Amides; D009587:Nitrogen Isotopes; D010446:Peptide Fragments; D011994:Recombinant Proteins; D001224:Aspartic Acid; D001216:Asparagine; D009113:Muramidase; D010450:Endopeptidases; D008666:Metalloendopeptidases; C058921:endoproteinase Asp-N