Photosynthetic Light-Harvesting (Antenna) Complexes—Structures and Functions

Abstract

Chlorophylls and bacteriochlorophylls, together with carotenoids, serve, noncovalently bound to specific apoproteins, as principal light-harvesting and energy-transforming pigments in photosynthetic organisms. In recent years, enormous progress has been achieved in the elucidation of structures and functions of light-harvesting (antenna) complexes, photosynthetic reaction centers and even entire photosystems. It is becoming increasingly clear that light-harvesting complexes not only serve to enlarge the absorption cross sections of the respective reaction centers but are vitally important in short- and long-term adaptation of the photosynthetic apparatus and regulation of the energy-transforming processes in response to external and internal conditions. Thus, the wide variety of structural diversity in photosynthetic antenna “designs” becomes conceivable. It is, however, common for LHCs to form trimeric (or multiples thereof) structures. We propose a simple, tentative explanation of the trimer issue, based on the 2D world created by photosynthetic membrane systems.

Reversible Electronic Energy Transfer (Homo-FRET) in Cyclic Molecular and Supramolecular Systems: Fluorescence Anisotropy Decays for the Isotropic Interaction

“…In particular, square, 3,4 heptagonal, 5,6 and octogonal 7 fluorescent systems undergoing homotransfer are known. Triangular units are also ubiquitous in photosynthetic systems, 8 where FRET (both homo-and hetero-) plays a major role in the complex light-harvesting process. 8,9 In this work, results for the general regular polygon are derived, under the assumption of isotropic interactions between nearest neighbors only.…”

“…Triangular units are also ubiquitous in photosynthetic systems, 8 where FRET (both homo-and hetero-) plays a major role in the complex light-harvesting process. 8,9 In this work, results for the general regular polygon are derived, under the assumption of isotropic interactions between nearest neighbors only. The extreme case of an infinite number of fluorophores (infinite polygon) is also considered.…”

“…In particular, square, , heptagonal, , and octogonal fluorescent systems undergoing homotransfer are known. Triangular units are also ubiquitous in photosynthetic systems, where FRET (both homo- and hetero-) plays a major role in the complex light-harvesting process. , …”

Chlorophylls: A Personal Snapshot

“…A huge Bchl-complex largely devoid of protein is the chlorosome of green bacteria. Its structure is largely determined by BChl–BChl interactions between members of the BChl c , d and e family [ 47 , 48 , 49 ]. The group of Jürgen Köhler has used linear dichroism of single light-harvesting complexes from purple photosynthetic bacteria to obtain information on the pigment arrangement and its excitonic coupling [ 50 ].…”

“…The role of carotenoids is, however, multi-faceted. As reviewed by Lokstein et al in this issue [ 49 ], they often participate in light-harvesting, transferring their excitation with good to excellent quantum yields to Chls. Additionally, Makhneva et al [ 53 ] presented an example from purple bacteria where the protective function against one ROS, e.g., singlet oxygen, seems negligible.…”