The photodamage process of pigments and proteins of PSI complexes from Spinacia Oleracea L.

Purified PSI complexes from Spinacia Oleracea L. were exposed to the strong light (PFD=2300 mu mol m(-2)s(-2)) for various period. Along with the illu mination the photodamage process of pigments and proteins of PSI complexes was investigated using absorption, fluorescence, circular dichroism. (CD) s pectroscopy and SDS-PAGE. It was found from the optical absorption spectra that the maximal absorbance of PSI complexes decreased and maximal peaks bl ue-shifted during the illumination, and the forth derivative spectra demons trated that the absorbance decreasing at red region mainly resulted from th e aborbance decreasing of the long wavelength Chla, implying that the long- wavelength Chla was readily to be bleached. The CD signals contributed by L HCI decreased more rapidly than other CD signals contributed. by Chla and C arotenoid, indicating that the LHCI was more sensitive to light than core c omplexes. It was observed by SDS-PAGE that some small polypeptides of PSI c omplexes were damaged earlier than reaction center proteins PsaA and PsaB. Lhca3, Lhca2 and PsaD were the early degraded proteins during illumination. In addition, it is also observed that the insoluble-cohesive-denatured pro teins appeared after prolonged illumination.