Spectroscopic studies of the tyrosine residues of human plasma apolipoprotein A-II

John B. Massey, Henry J. Pownall

Research output: Contribution to journalArticle

3 Scopus citations

Abstract

Human apolipoprotein A-II (apo A-II) in solution and associated with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) was investigated by a combination of absorbance and fluorescence methods. Each apo A-II polypeptide chain contains four tyrosine residues but no tryptophan residues. Two and three tyrosine residues, respectively, appear to be buried for apo A-II in aqueous solution and in the lipid-associated protein. The spectroscopic properties of the tyrosine residues of lipid-associated apo A-II were also investigated. Plots of fluorescence intensity against temperature revealed a discontinuity in the region of the phase transition; however, over the same temperature range, there was no change in the exposure of tyrosine residues to the aqueous environment or in their mobility as measured by fluorescence polarization. Near-ultraviolet circular dichroic measurements demonstrated that the environments of the tyrosine residues of lipid-associated apo A-II and nitrated apo A-II were different from that of the apo A-II in solution or in a denatured state. Similar measurements also revealed that the microenvironments around tyrosines of apo A-II bound to DMPC in the gel phase are different from those observed in the liquid crystalline phase. Using environmentally sensitive fluorescence lipid probes, we have previously demonstrated that the polarity of the lipid/water interface of DMPC changes through a phase transition. The observations presented here indicate that these environmental changes also occur at the lipid/protein interface.

Original languageEnglish (US)
Pages (from-to)111-120
Number of pages10
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Volume999
Issue number2
DOIs
StatePublished - Nov 30 1989

Keywords

  • (Human plasma)
  • Apolipoprotein A-II
  • Spectroscopy
  • Tyrosine residue

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology
  • Biophysics
  • Biochemistry

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