Conformational differences of oxytocin and vasopressin as observed by fluorescence anisotropy decays and transient effects in collisional quenching of tyrosine fluorescence

Ignacy Gryczynski, Henryk Szmacinski, Gabor Laczko, Wieslaw Wiczk, Michael L. Johnson, Jozef Kusba, Joseph R. Lakowicz

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

We used gigahertz frequency-domain fluorometry to examine the tyrosyl fluorescence intensity and anisotropy decays of the single-tyrosine cyclic peptide hormones oxytocin and vasopressin. Acrylamide quenching and a distance-dependent quenching model for collisional quenching were used to evaluate the extent of tyrosyl exposure to the quencher and to provide increased resolution of the picosecond anisotropy decays. Analysis of the intensity decays using a lifetime distribution model shows different distributions for oxytocin and vasopressin. We found that the tyrosyl fluorescence of lysine-vasopressin, as revealed both by the lifetime Stern-Volmer plots and from the quenching analysis, is quenched more effectively than oxytocin. For N-acetyltyrosinamide (NATyrA), oxytocin, and lysine-vasopressin, we recovered apparent diffusion coefficients for quenching of 4.7×10-6, 0.44×10-6, and 4.3×10-6 cm2/s, respectively, the lower value for oxytocin suggesting a shielded environment for its tyrosyl residue. Tyrosyl anisotropy decays were recovered by global analysis of progressively quenched samples. Compared with oxytocin, vasopressin displayed a longer correlation time for overall rotational diffusion and a higher amplitude for picosecond segmented motions of its tyrosyl residue. All the data are consistent with a more extended and flexible solution structure for vasopressin than for oxytocin.

Original languageEnglish
Pages (from-to)163-176
Number of pages14
JournalJournal of Fluorescence
Volume1
Issue number3
DOIs
StatePublished - Sep 1991

Keywords

  • Oxytocin
  • collisional quenching
  • fluorescence anisotropy decays
  • fluorescence intensity
  • tyrosine fluorescence
  • vasopressin

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