ABSTRACT: Light-induced chlorophyll a (Chl a) fluorescence quenching was studied in light-harvesting complex of photosystem II (LHCII).
Fluorescence intensity decreased by ca. 20% in the course of 20 min illumination (412 nm, 36 Amol m�2 s�1) and was totally reversible
within 30 min dark adaptation. The pronounced quenching was observed only in LHCII in an aggregated form and exclusively in the
presence of molecular oxygen. Structural rearrangement of LHCII correlated to the quenching was monitored by measuring changes in UV–
Visible light absorption spectra, and by measuring Fourier-transform infrared spectroscopy (FTIR) in the Amide I region of the protein
(1600–1700 cm�1). The light-induced structural rearrangement of LHCII was interpreted as a partial disaggregation of the complex based on
the decrease in the light scattering signal and the characteristic features observed in the FTIR spectra: the relative increase in the intensity of
the band at 1653 cm�1, corresponding to a protein in the a-helical structure at the expense of the band centered at 1621 cm � 1, characteristic
of aggregated forms. The fact that the light-driven isomerization of the all-trans violaxanthin to the 13-cis form was not observed under the
non-oxygenic conditions coincided with the lack of large-scale conformational reorganization of LHCII. The kinetics of this large-scale
structural effect does not correspond to the light-induced fluorescence quenching, in contrast to the kinetics of structural changes in LHCII
observable at low oxygen concentrations. Photo-conversion of 5% of the pool of all-trans violaxanthin to 9-cis isomer was observed under
such conditions. Possible involvement of the violaxanthin isomerization in the process of structural rearrangements and excitation quenching
in LHCII is discussed. D 2002 Elsevier Science B.V. All rights reserved.
Biochimica et Biophysica Acta (BBA) - Bioenergetics 01/2002; 1554:108– 117. · 4.84 Impact Factor