PHOTOINACTIVATION OF ISOLATED D1 D2/CYTOCHROME-B559 COMPLEX UNDER AEROBIC AND ANAEROBIC CONDITIONS/

The preparation of D1/D2/cytochrome b559 complex isolated from pea (Pi sum sativum L.) was photoinactivated by ''white light'' (140 W m-2) at 20 and 4-degrees-C in both the presence and absence of oxygen. The in activation was followed by measuring the decline of the photoinduced a bsorbance change DELTAA683 (the photoaccumulation of reduced pheophyti n), by measuring absorption spectra and fluorescence emission, and by polypeptide analysis. In the presence of oxygen, the ability of the D1 /D2/cyt b559 complex to accumulate reduced pheophytin was lost with th e halftime tau1/2 of about 3 min and fluorescence quantum yield declin ed with tau1/2 of about 30 min at both 20 and 4-degrees-C. The D1 and D2 polypeptides were rapidly modified at 20-degrees-C as reflected by the presence of their large aggregates at the start of the electrophor etic gel and by a decrease of the mobility of remaining D1 and D2 mono mers. This modification was substantially limited at 4-degrees-C. Subu nits of cytochrome b559 were not modified at any temperature. When oxy gen was removed, the halftime of the DELTAA683 decline increased by ab out one order of magnitude, fluorescence emission did not decline, but slightly increased, and the polypeptide pattern was only slightly aff ected during irradiation.