Complex formation between chlorophyll a and cytochrome c: surface properties at the air-water interface. Absorbance, fluorescence and fluorescence-lifetime in Langmuir-Blodgett films.
The binding of cytochrome c to an insoluble monolayer of chlorophyll a was studied. Surface pressure (II), surface potential (delta V) and [14C]cytochrome c surface-concentration (gamma) isotherms were measured versus molecular area (sigma) in mixed films. Compared to the successive-addition method, this procedure allows the formation of homogeneous mixed films. The cytochrome c is incorporated into a chlorophyll a monolayer, compressed at a surface pressure of 20 mN.m-1. On expansion, the quantity of protein incorporated into the monolayer gradually increases. Subsequent compression-expansion cycles result in similar isotherms, distinct from that measured during the first expansion. All surface properties measured, but more specifically the surface radioactivity of [14C]cytochrome c, indicate the irreversibility of protein incorporation into the chlorophyll a monolayer. In fact, surface properties of the binary film are completely different from the properties of either of the pure components. As a result, calculated values of surface potentials for mixed films using the additivity law deviate from experimentally measured potentials. The absorption and fluorescence spectra of mixed films transferred onto a solid substrate by the Langmuir-Blodgett technique, indicate a dilution effect of chlorophyll a by cytochrome c. However, the dilution effect cannot be detected by the fluorescence lifetimes of pure chlorophyll a and mixed chlorophyll a-cytochrome c films, both shorter than 0.2 ns. This provides support for the existence of an energy-transfer mechanism between chlorophyll a monomer and chlorophyll a aggregates which could serve as an energy trap. The role of the protein could be related to that of the matrix.
Lamarche
F
F
Centre de recherche et de développement sur les aliments, Agriculture Canada, St-Hyacinthe, Québec.
Picard
G
G
Téchy
F
F
Aghion
J
J
Leblanc
R M
RM
D000596:Amino Acids / Q000032:analysis; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D003574:Cytochrome c Group / Q000737:chemistry* / Q000648:ultrastructure; D005453:Fluorescence; D008854:Microscopy, Electron; D013057:Spectrum Analysis; D013696:Temperature
D000596:Amino Acids; D003574:Cytochrome c Group; D002734:Chlorophyll; D000077194:Chlorophyll A