Functional heterogeneity of the fucoxanthins and fucoxanthin-chlorophyll proteins in diatom cells revealed by their electrochromic response and fluorescence and linear dichroism spectra

In this work, by analyzing the electrochromic transient spectra, the 77 K fluorescence emission and excitation, as well as the linear dichroism (LD) and circular dichroism (CD) spectra of low-light (LL) and high-light (HL) grown Phaeodactylum tricornutum cells, we show that the fucoxanthins (Fx) and fucoxanthin-chlorophyll proteins (FCP) exhibit marked functional heterogeneity. Electrochromic transients reveal that LL and HL cells differ substantially in their relative contents of two Fx forms, which absorb at 501 and 550 nm; they exhibit distinct LD signals but are CD silent. Fluorescence emission and excitation spectra at 77 K reveal that although both forms efficiently transfer excitation energy to Chl a, the red form feeds somewhat more energy to photosystem II than to photosystem I. Similar data obtained in Cyclotella meneghiniana cells suggest that the heterogeneity of the FCP pool, with different Fx forms, plays a role in the regulation of energy utilization in FCP-containing organisms. © 2010 Elsevier B.V. All rights reserved

How Light-Induced Charge Transfer Accelerates the Receptor-State Recovery of Photoactive Yellow Protein from its Signaling State

Stark (electroabsorption) spectra of the M100A mutant of photoactive yellow protein reveal that the neutral, cis cofactor of the pB intermediate undergoes a strikingly large change in the static dipole moment ([Formula: see text] = 19 Debye) on photon absorption. The formation of this charge-separated species, in the excited state, precedes the cis → trans isomerization of the pB cofactor and the regeneration of pG. The large [Formula: see text] , reminiscent of that produced on the excitation of pG, we propose, induces twisting of the cis cofactor as a result of translocation of negative charge, from the hydroxyl oxygen, O1, toward the C7-C8 double bond. The biological significance of this photoinduced charge transfer reaction underlies the significantly faster regeneration of pG from pB in vitro, on the absorption of blue light

The charge-transfer properties of the S-2 state of fucoxanthin in solution and in fucoxanthin chlorophyll-a/c(2) protein (FCP) based on stark spectroscopy and molecular-orbital theory

Fucoxanthin chlorophyll-a/