Light-induced changes in the chemical bond structure of light-harvesting complex II probed by FTIR spectroscopy.
Light-harvesting complex II (LHC-II) regulates the light energy distribution between photosystem I and II in plants. This process is mediated by phosphorylation of the LHC-II protein, which depends on the oxidation state of photosynthetic electron carriers. In addition to this regulatory mechanism, it has recently been proposed that light can directly induce a conformational change in isolated LHC-II. To provide biophysical evidence for such a conformational change in the protein, we studied infrared absorbance changes in isolated LHC-II upon exposure to light flashes. Compared to the signals obtained with other proteins that exhibit well-characterized conformational changes, the signal in the LHC-II difference spectra is very weak. The position of the difference bands coincides with the main IR absorption bands of chlorophyll. We conclude that there are no detectable light-induced changes in the LHC protein structure and attribute the observed IR signals to light-induced chlorophyll degradation.
Rogl
Hans
H
Max-Planck-Institut für Biophysik, Heinrich-Hoffmann-Strasse 7, D-60528 Frankfurt am Main, Germany. hans.rogl@gmx.net
Kühlbrandt
Werner
W
Barth
Andreas
A
D008027:Light; D045342:Light-Harvesting Protein Complexes; D018532:Pisum sativum / Q000737:chemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000528:radiation effects*; D045331:Photosystem I Protein Complex; D011487:Protein Conformation; D017550:Spectroscopy, Fourier Transform Infrared
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex