ENERGY TRANSFER FROM CAROTENOIDS TO CHLOROPHYLL a IN BLACK LIPID MEMBRANES

Macular pigment in henle fiber membranes:A model for Haidinger's brushes

The dichroic properties of lutein, presumed to be the macular pigment, are demonstrated and the structure of Henle fiber membranes is discussed. A consequence of the pigment molecules being incorporated into the bilipid components of these membranes is shown to be the production of Haidinger's brushes. Spectra of lutein in association with phospholipid model membranes at different temperatures are presented and these support the theory that such incorporation occurs. Additional experiments test an alternative model for Haidinger's brushes and show it to be inconsistent with the spectroscopic properties of lutein.

Excitation energy transfer between β-carotene and chlorophyll-a in various systems

The excitation energy transfer from β-carotene to chlorophyll-a in several seminatural systems such as liposomes, lipid layers and PSI complex has been studied at room and liquid nitrogen temperature. Only in a case of PSI complex an efficient energy transfer (about 30%) from β-carotene to chlorophyll-a has been observed. The results of energy transfer were discussed on the ground of Dexter's mechanism by taking into account the recently discovered energy level ((1)Ag) of β-carotene.

Energy transfer in artificial membrane systems. Singlet-singlet energy transfer from alloxazines to isolloxazines in dipamitoyl phosphatidylcholine liposomes and dialkylammonium chloride vesicles

The singlet-singlet energy transfer from alloxazines to isoalloxazines has been investigated in dialmitoyl phosphatidylcholine (DPPC) liposomes and dioctadecyltrimethylammonium chloride (2C18NC) vesicles to clarify the role of the artificial membranes in the energy transfer phenomenon. The structures of the artificial membranes were divided into two types: the single-walled (sonicated DPPC) and the multi-compartment vesicles (unsonicated DPPC and sonicated 2C18NC). In the DPPC single-walled liposomes, the energy of the donor lost by quenching is efficiently transferred to the acceptor via the Förster-type dipoledipole interaction. In the case of multi-compartment liposomes of DPPC, the mean distance between donor and acceptor is so small because the external surface of a bilayer is in the vicinity of the internal surface of another bilayer. As a consequence, efficiencies both of energy transfer and of energy loss were greater than those in single-walled liposomes. The fluid property of the 2C18NC bilayer allowed the preferential collisional quenching. The marked reduction in the efficiencies of both energy transfer and energy loss were attributed to the elongation of donor-acceptor distances due to the increase of the size of liposome.

Photo-voltages of bilayer lipid membranes in the presence of cyanine dyes

The transmembrane photo-voltage waveforms induced by 10 different cyanine dyes absorbed to one side of bilayer lipid membranes are described. The membranes were prepared from lecithin, oxidized cholesterol, and mixed lecithin and oxidized cholesterol. An 8-mus flash illumination was used. Three dyes induced a photo-voltage which developed in a few milliseconds, then discharged in less than the membranes' resistance-capacitance time. Five dyes induced a photo-voltage which increased for much longer than the membranes' resistance-capacitance time. Two dyes did not induce any photo-electric effects. Models are presented which correlate the dye structure with the type of photo-voltage waveform induced.

Energy transfer by chlorophyll a in detergent micelles

The process of energy transfer was studied in the chlorophyll a-containing detergent micelle, serving as a possible model of the photosynthetic unit. Chlorophyll a was added to aqueous solutions of the detergent Triton X-100 and incorporated into the micelles. The energy transfer process was studied by investigating the concentration depolarization of fluorescence of chlorophyll a. On the basis of the experimental depolarization curves as well as the value of the Förster parameter Ro equals to 56 A calculated from the overlap of absorption and fluorescence spectra it was concluded that energy transfer between chlorophyll a molecules in this model follows the Förster-type mechanism of inductive resonance. Furthermore it was found that the local concentration of chlorophyll a in the micelles is higher by 1-3 orders of magnitude than its overall concentration in the solution and by choosing the appropriate ratio between the consentration of chlorophyll a and the detergent it is possible to reach the in vivo chlorophyll concentration of 0.1 M withing the micelles. Thus the chlorophyll-detergent micelle model may be applied as a model of the separate package-type photosynthetic unit.