Pheophytin-protein interactions in photosystem II studied by resonance Raman spectroscopy of modified reaction centers.
Soret-excited resonance Raman spectra of two types of pheophytin-exchanged photosystem II RCs are reported. The cofactor composition of the reaction centers was modified by exchanging pheophytin a for 13(1)-deoxo-13(1)-hydroxypheophytin a, yielding one preparation with selective replacement of the photochemically inactive pheophytin (H(B)) and a second one exhibiting total replacement of H(B) and 40% replacement of H(A), the primary electron acceptor. Resonance Raman spectra indicate that the other bound cofactors present are not significantly perturbed by Pheo substitution. The resonance Raman contributions from H(A) and H(B) in the carbonyl stretching region are identified at 1679 and 1675 cm(-)(1), respectively, indicating that both pheophytin molecules in the photosystem II reaction center have hydrogen-bonded keto-carbonyl groups. This conclusion differs from what is observed in the functionally related RCs of purple non-sulfur bacteria, where the keto-carbonyl group of H(B) is not hydrogen bonded, but confirms predictions from models based on protein sequence alignments.
Germano
Marta
M
Huygens Laboratory, Biophysics Department, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands. marta@nat.vu.nl
Pascal
Andy
A
Shkuropatov
Anatoli Ya
AY
Robert
Bruno
B
Hoff
Arnold J
AJ
van Gorkom
Hans J
HJ
D001665:Binding Sites; D003594:Cytoplasmic Granules / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins / Q000737:chemistry*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman / Q000379:methods; D018724:Spinacia oleracea / Q000737:chemistry
D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex