PUMA
Istituto di Biofisica     
Fissi A., Pieroni O., Angelini N., Lenci F. Photoresponsive Polypeptides. Photochromic and Conformational Behavior of Spiropyran-Containing Poly(l-glutamate)s under Acid Conditions. In: Macromolecules, vol. 32 (21) pp. 7116 - 7121. ACS, 1999.
 
 
Abstract
(English)
In photoresponsive ciliates, like Blepharisma japonicum and Stentor coeruleus, the photoreceptor pigments responsible for photomotile reactions are hypericin-type chromophores packed in highly osmiophilic subpellicular granules. Liposomes loaded with hypericin can constitute a simple model system, appropriate for understanding the primary light-induced molecular events triggering the sensory chain in these microorganisms. Optical absorption, steady-state and time-resolved fluorescence and pulsed photoacoustic calorimetry have been used to measure spectral distributions, fluorescence lifetimes, radiati ve and radiationless transition quantum yields of hypericin when assembled into egg Lo phosphatidylcholine liposomes. With respect to hypericin ethanol solutions, both absorption and fluorescence maxima are 5 nm l'ed shifted when the pigment is inserted into the lipidic microenvironment,regardless of the hypericin local concentration. Increasing by 100 times the hypericin local concentration decreases the relative fluorescence quantum yield by a factor of around 150 and the fraction of thermally released energy, conversely, increases from 0.6 to 0.9. From the analysis of fluorescence lifetimes and their relative amplitudes it appears that a subnanosecond living component is predominant at the highest hypericin local concentrations.
DOI: 10.1021/ma990796q
Subject Polypeptides


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