title: The formation of oxytocin dimers is suppressed by the zinc-aspartate-oxytocin complex.
abstract: The aim of this study was to investigate the effect of divalent metal ions (Ca, Mg(2+) , and Zn(2+) ) on the stability of oxytocin in aspartate buffer (pH 4.5) and to determine their interaction with the peptide in aqueous solution. Reversed-phase high-performance liquid chromatography and high-performance size-exclusion chromatography measurements indicated that after 4 weeks of storage at 55°C, all tested divalent metal ions improved the stability of oxytocin in aspartate-buffered solutions (pH 4.5). However, the stabilizing effects of Zn(2+) were by far superior compared with Ca(2+) and Mg(2+) . Liquid chromatography-tandem mass spectrometry showed that the combination of aspartate and Zn(2+) in particular suppressed the formation of peptide dimers. As shown by isothermal titration calorimetry, Zn(2+) interacted with oxytocin in the presence of aspartate buffer, whereas Ca(2+) or Mg(2+) did not. In conclusion, the stability of oxytocin in the aspartate-buffered solution is strongly improved in the presence of Zn(2+) , and the stabilization effect is correlated with the ability of the divalent metal ions in aspartate buffer to interact with oxytocin. The reported results are discussed in relation to the possible mode of interactions among the peptide, Zn(2+) , and buffer components leading to the observed stabilization effects.
authors.affiliation: Department of Pharmaceutics, Faculty of Pharmacy, University of Surabaya (Ubaya), Surabaya, Indonesia; Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, Groningen, The Netherlands. Electronic address: c_avanti@staff.ubaya.ac.id.
authors.forename: Christina
authors.initials: C
authors.lastname: Avanti
authors.affiliation: Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, Groningen, The Netherlands.
authors.forename: Wouter L J
authors.initials: WLJ
authors.lastname: Hinrichs
authors.affiliation: Pharmacokinetics, Toxicology and Targeting, Research Institute of Pharmacy, University of Groningen, Groningen, The Netherlands.
authors.forename: Angela
authors.initials: A
authors.lastname: Casini
authors.affiliation: Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, Groningen, The Netherlands.
authors.forename: Anko C
authors.initials: AC
authors.lastname: Eissens
authors.affiliation: Mass Spectrometry Core Facility, University of Groningen, Groningen, The Netherlands.
authors.forename: Annie
authors.initials: A
authors.lastname: Van Dam
authors.affiliation: Department of Molecular Microbiology, University of Groningen, Groningen, The Netherlands.
authors.forename: Alexej
authors.initials: A
authors.lastname: Kedrov
authors.affiliation: Department of Molecular Microbiology, University of Groningen, Groningen, The Netherlands.
authors.forename: Arnold J M
authors.initials: AJM
authors.lastname: Driessen
authors.affiliation: Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, Groningen, The Netherlands.
authors.forename: Henderik W
authors.initials: HW
authors.lastname: Frijlink
authors.affiliation: Mass Spectrometry Core Facility, University of Groningen, Groningen, The Netherlands.
authors.forename: Hjalmar P
authors.initials: HP
authors.lastname: Permentier
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry*; D002021:Buffers; D002413:Cations, Divalent / Q000737:chemistry; D002850:Chromatography, Gel; D056148:Chromatography, Reverse-Phase; D019281:Dimerization; D004355:Drug Stability; D010121:Oxytocin / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D002021:Buffers; D002413:Cations, Divalent; D001224:Aspartic Acid; D010121:Oxytocin; D015032:Zinc