Complexation of chlorophyll a and cytochrome c in monolayer at air-water interface

Ahmed Es-Sounni, Wieslaw I. Gruszecki, Heider Ali Tajmir-Riahi, Bogumil Zelent, Gongming Wang, Roger M. Leblanc

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Abstract

The chlorophyll (chl) a-cytochrome (cyt) c mixed system was studied in Langmuir films at the air-water interface and Langmuir-Blodgett films. Surface pressure-molecular area isotherms measured for pure and mixed components were discussed in terms of ideal mixing processes. The negative deviations from ideality observed at cyt c molar fractions lower than 0.1 can be interpreted as a result of pigment-protein complexation. On the other hand, at protein molar fractions higher than 0.1, progressive positive deviations were observed and could be due to cyt c aggregation in the mixed system. Furthermore, the spontaneous complexation of the chl a and cyt c (in solution) was observed in hydrated ethanol (water:ethanol, 97:3). In this case, the protein molar fraction was found to be 0.2. Langmuir-Blodgett films of the chlorophyll-protein mixtures were also analyzed using absorption, Fourier transform infrared, and fluorescent spectroscopic techniques. The infrared spectroscopy showed that at protein molar fractions higher than 0.1, cyt c molecules undergo drastic conformational changes from α-helix to β-sheet and turn structures. Such conformational changes are interpreted in terms of protein aggregation and denaturation. Spectroscopic evidence has also indicated the participation of the keto group in the chlorophyll-protein interaction and the presence of chlorophyll molecules in an aggregated form in the complexes.

Original languageEnglish (US)
Pages (from-to)134-141
Number of pages8
JournalJournal of Colloid And Interface Science
Volume171
Issue number1
DOIs
StatePublished - Apr 1995

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Colloid and Surface Chemistry

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