title: Peridinin chlorophyll a protein: relating structure and steady-state spectroscopy.
abstract: Peridinin chlorophyll a protein (PCP) from Amphidinium carterae has been studied using absorbance (OD), linear dichroism (LD), circular dichroism (CD), fluorescence emission, fluorescence anisotropy, fluorescence line narrowing (FLN), and triplet-minus-singlet spectroscopy (T-S) at different temperatures (4-293 K). Monomeric PCP binds eight peridinins and two Chls a. The trimeric structure of PCP, resolved at 2 A [Hofmann et al. (1996) Science 27, 1788-1791], allows modeling of the Chl a-protein and Chl a-Chl a interactions. The FLN spectrum shows that Chl a is not or is very weakly hydrogen-bonded and that the central magnesium of the emitting Chl a is monoligated. Simulation of the temperature dependence of the absorption spectra indicates that the Huang-Rhys factor, characterizing the electron-phonon coupling strength, has a value of approximately 1. The width of the inhomogeneous distribution function is estimated to be 160 cm(-)(1). LD experiments show that the two Chls a in PCP are essentially isoenergetic at room temperature and that a substantial amount of PCP is in a trimeric form. From a comparison of the measured and simulated CD, it is concluded that the interaction energy between the two Chls a within one monomer is very weak, <10 cm(-)(1). In contrast, the Chls a appear to be strongly coupled to the peridinins. The 65 cm(-)(1) band that is visible in the low-frequency region of the FLN spectrum might indicate a Chl a-peridinin vibrational mode. The efficiency of Chl a to peridinin triplet excitation energy transfer is approximately 100%. On the basis of T-S, CD, LD, and OD spectra, a tentative assignment of the peridinin absorption bands has been made.
authors.affiliation: Faculty of Sciences, Division of Physics and Astronomy, and Institute for Condensed Matter Physics and Spectroscopy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors.forename: F J
authors.initials: FJ
authors.lastname: Kleima
authors.forename: M
authors.initials: M
authors.lastname: Wendling
authors.forename: E
authors.initials: E
authors.lastname: Hofmann
authors.forename: E J
authors.initials: EJ
authors.lastname: Peterman
authors.forename: R
authors.initials: R
authors.lastname: van Grondelle
authors.forename: H
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D000818:Animals; D002338:Carotenoids / Q000737:chemistry*; D004141:Dinoflagellida; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D015800:Protozoan Proteins; C073227:peridinin chlorophyll-a protein, Dinophyceae; D002338:Carotenoids