Abstract:
:The possibility that the chlorophyll (chl) ring distortions observed in the crystal structures of chl-protein complexes are involved in the transition energy modulation, giving rise to the spectral forms, is investigated. The out-of-plane chl-macrocycle distortions are described using an orthonormal set of deformations, defined by the displacements along the six lowest-frequency, out-of-plane normal coordinates. The total chl-ring deformation is the linear combination of these six deformations. The two higher occupied and the two lower unoccupied chl molecular orbitals, which define the Q(y) electronic transition, have the same symmetry as four of the six out-of-plane lowest frequency modes. We assume that a deformation along the normal-coordinate having the same symmetry as a given molecular orbital will perturb that orbital and modify its energy. The changes in the chl Q(y) transition energies are evaluated in the Peridinin-Chl-Protein complex and in light harvesting complex II (LHCII), using crystallographic data. The macrocycle deformations induce a distribution of the chl Q(y) electronic energy transitions which, for LHCII, is broader for chla than for chlb. This provides the physical mechanism to explain the long-held view that the chla spectral forms in LHCII are both more numerous and cover a wider energy range than those of chlb.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Zucchelli G,Brogioli D,Casazza AP,Garlaschi FM,Jennings RCdoi
10.1529/biophysj.107.104554subject
Has Abstractpub_date
2007-09-15 00:00:00pages
2240-54issue
6eissn
0006-3495issn
1542-0086pii
S0006-3495(07)71479-0journal_volume
93pub_type
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