title: Thermodynamic and fluorescence analyses to determine mechanisms of IgG1 stabilization and destabilization by arginine.
abstract: OBJECTIVE
  To investigate mechanisms governing the stabilization and destabilization of immunoglobulin (IgG1) by arginine (Arg).
  
  
  METHODS
  The effects of Arg on the aggregation/degradation, thermodynamic stability, hydrophobicity, and aromatic residues of IgG1 were respectively investigated by size-exclusion chromatography, differential scanning calorimetry, probe fluorescence, and intrinsic fluorescence.
  
  
  RESULTS
  Arg monohydrochloride (Arg-HCl) suppressed IgG1 aggregation at near-neutral pH, but facilitated aggregation and degradation at acidic pH or at high storage temperature. Equimolar mixtures of Arg and aspartic acid (Asp) or glutamic acid (Glu) suppressed aggregation without facilitating degradation even at high temperature. Arg-HCl decreased the thermodynamic stability of IgG1 by enthalpic loss, which was counteracted by using Asp or Glu as a counterion for Arg. The suppression of aggregation by Arg-HCl was well correlated with the decrease in hydrophobicity of IgG1. The intrinsic fluorescence of IgG1 was unaffected by Arg-HCl.
  
  
  CONCLUSIONS
  Suppression of IgG1 aggregation can be attributed to the interaction between Arg and hydrophobic residues; on the other hand, facilitation of aggregation and degradation is presumably due to the interaction between Arg and some acidic residues, which could be competitively inhibited by simultaneously adding either Asp or Glu.
authors.affiliation: Product Engineering Department, Chugai Pharmaceutical Co., Ltd., 5-5-1 Ukima, Kita-ku, Tokyo, 115-8543, Japan, fukuda.masakazu76@chugai-pharm.co.jp.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukuda
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kameoka
authors.forename: Takuya
authors.initials: T
authors.lastname: Torizawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Saitoh
authors.forename: Masaya
authors.initials: M
authors.lastname: Yasutake
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Imaeda
authors.forename: Akiko
authors.initials: A
authors.lastname: Koga
authors.forename: Akihiko
authors.initials: A
authors.lastname: Mizutani
mesh_terms: D001120:Arginine / Q000737:chemistry*; D004355:Drug Stability; D005453:Fluorescence; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis* / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013816:Thermodynamics
chemical_list: D007074:Immunoglobulin G; D001120:Arginine