title: Deamidation of the asparaginyl-glycyl sequence.
abstract: The deamidation of Ac-Asn-Gly-NHMe and Ac-Isn-Gly-NHMe has been studied as a model for the facile deamidation of the Asn-Gly sequence in proteins. At alkaline pH, the product in each case is an identical mixture of Ac-alpha-Asp-Gly-NHMe (approximately 22%) and Ac-beta-Asp-Gly-NHMe (approximately 78%) as determined by n.m.r. spectroscopy. Because this same ratio is obtained from both Ac-Asn-Gly-NHMe and Ac-Isn-Gly-NHMe, the postulated mechanism, that deamidation proceeds through a cyclic imide intermediate, is confirmed. Unlike peptides of aspartyl esters, cyclization does not occur under nonaqueous conditions or at low pH in aqueous solution.
mesh_terms: D000595:Amino Acid Sequence; D001216:Asparagine; D055598:Chemical Phenomena; D002621:Chemistry; D004151:Dipeptides; D005998:Glycine; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D011506:Proteins
chemical_list: D004151:Dipeptides; D011506:Proteins; C049694:acetyl-isoasparaginyl-methylglycinamide; C049693:acetyl-asparaginyl-methylglycinamide; D001216:Asparagine; D005998:Glycine