Photo-oxidation of P740, the primary electron donor in photosystem I from Acaryochloris marina.
Fourier transform infrared spectroscopy (FTIR) difference spectroscopy in combination with deuterium exchange experiments has been used to study the photo-oxidation of P740, the primary electron donor in photosystem I from Acaryochloris marina. Comparison of (P740(+)-P740) and (P700(+)-P700) FTIR difference spectra show that P700 and P740 share many structural similarities. However, there are several distinct differences also: 1), The (P740(+)-P740) FTIR difference spectrum is significantly altered upon proton exchange, considerably more so than the (P700(+)-P700) FTIR difference spectrum. The P740 binding pocket is therefore more accessible than the P700 binding pocket. 2), Broad, "dimer" absorption bands are observed for both P700(+) and P740(+). These bands differ significantly in substructure, however, suggesting differences in the electronic organization of P700(+) and P740(+). 3), Bands are observed at 2727(-) and 2715(-) cm(-1) in the (P740(+)-P740) FTIR difference spectrum, but are absent in the (P700(+)-P700) FTIR difference spectrum. These bands are due to formyl CH modes of chlorophyll d. Therefore, P740 consists of two chlorophyll d molecules. Deuterium-induced modification of the (P740(+)-P740) FTIR difference spectrum indicates that only the highest frequency 13(3) ester carbonyl mode of P740 downshifts, indicating that this ester mode is weakly H-bonded. In contrast, the highest frequency ester carbonyl mode of P700 is free from H-bonding. Deuterium-induced changes in (P740(+)-P740) FTIR difference spectrum could also indicate that one of the chlorophyll d 3(1) carbonyls of P740 is hydrogen bonded.
Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA.
Velautham
V
Sivakumar
Ruili
R
Wang
Gary
G
Hastings
D000458:Cyanobacteria / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D004579:Electron Transport; D008027:Light; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000528:radiation effects*; D011166:Porphyrins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D013045:Species Specificity; D017550:Spectroscopy, Fourier Transform Infrared; D013329:Structure-Activity Relationship
C487614:P740 compound; D045331:Photosystem I Protein Complex; D011166:Porphyrins