title: Effects of acidic N + 1 residues on asparagine deamidation rates in solution and in the solid state.
abstract: The deamidation kinetics of four model peptides (AcGQNGG, AcGQNDG, AcGQNEG, and AcGQNQG) were studied in solution (70 degrees C, pH 5-10) and in lyophilized solids [70 degrees C, 50% relative humidity, "effective pH" ('pH') 5-10] containing polyvinyl pyrrolidone. AcGQNGG, AcGQNEG, and AcGQNQG degraded exclusively through Asn deamidation, whereas AcGQNDG also displayed Asp isomerization, and Asp-Gly peptide bond cleavage. The pH/'pH'-rate profiles were consistent with a shift in the rate-determining step of Asn deamidation from carbonyl addition to expulsion of ammonia with increasing pH. In solution, AcGQNGG deamidated up to 38-fold faster than the other peptides, indicating the importance of steric effects of the N + 1 residue. AcGQNGG and AcGQNQG had up to 60 times slower rates of deamidation in the solid state than in solution. In contrast, the deamidation rates of AcGQNEG and AcGQNDG in the solid state were similar to those in solution. N + 1 Glu or Asp residue may enhance local hydration, so that the deamidation of Asn in the solid formulations actually proceeds in a solution-like environment.
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, 2095 Constant Avenue, Lawrence, Kansas 66047, USA.
authors.forename: Bei
authors.initials: B
authors.lastname: Li
authors.forename: Eric M
authors.initials: EM
authors.lastname: Gorman
authors.forename: Kimberly D
authors.initials: KD
authors.lastname: Moore
authors.forename: Todd
authors.initials: T
authors.lastname: Williams
authors.forename: Richard L
authors.initials: RL
authors.lastname: Schowen
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Topp
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Borchardt
mesh_terms: D000577:Amides / Q000737:chemistry*; D001216:Asparagine / Q000032:analysis / Q000737:chemistry*; D001224:Aspartic Acid / Q000737:chemistry; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D009842:Oligopeptides / Q000032:analysis / Q000737:chemistry; D019999:Pharmaceutical Solutions / Q000032:analysis / Q000737:chemistry
chemical_list: D000577:Amides; D009842:Oligopeptides; D019999:Pharmaceutical Solutions; D001224:Aspartic Acid; D001216:Asparagine