Effect of N-1 and N-2 residues on peptide deamidation rate in solution and solid state.
The deamidation kinetics of 7 model peptides (VYPNGA, VYGNGA, VFGNGA, VIGNGA, VGGNGA, VGPNGA, and VGYNGA) were studied at 70 degrees C in pH 10 buffer solutions and at 70 degrees C and 50% relative humidity in lyophilized solid formulations containing polyvinyl pyrrolidone (PVP). The disappearance of the model peptides from solution and solid-state formulations followed apparent first-order kinetics, proceeding to completion in solution. In the solid state, the reactions showed plateaus with approximately 10% to 30% of the model peptides remaining; this was thought to be due to reversible complexation of the peptides and the PVP followed by slow dissociation of the complexes. The residues immediately N-terminal to asparagine (N-1, N-2) influenced the rate of deamidation significantly in the solid state but had minimal effect in solution. Increases in the volume and hydrophobicity of the N-1 and N-2 residues decreased the rate of deamidation in the solid state, but neither parameter alone adequately accounted for the observed effects. An empirical model using a linear combination of volume and hydrophobicity was developed; it showed that the influences of the volume and the hydrophobicity of the residues in the N-1 and N-2 positions are approximately equally important for the N-1 and N-2 residues.
Li
Bei
B
Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS 66047, USA.
Schowen
Richard L
RL
Topp
Elizabeth M
EM
Borchardt
Ronald T
RT
D000577:Amides / Q000378:metabolism*; D001216:Asparagine / Q000737:chemistry*; D008956:Models, Chemical; D010446:Peptide Fragments / Q000737:chemistry* / Q000493:pharmacokinetics*; D010455:Peptides / Q000737:chemistry / Q000493:pharmacokinetics; D012995:Solubility; D012996:Solutions
D000577:Amides; D010446:Peptide Fragments; D010455:Peptides; D012996:Solutions; D001216:Asparagine