LIGHT-INDUCED AEROBIC DEGRADATION OF D1 D2/CYT B559 PREPARATIONS FROMSPINACH ANALYZED BY LOW-TEMPERATURE SPECTROSCOPY/

The radiant energy induced degradation at 293 K of isolated D1/D2/cyt b559 complexes from spinach was investigated under aerobic conditions by measurements of absorption and emission spectra between 1.1 and 270 K. In the 1.1 K absorption spectrum a bleaching and slight blue shift at 679 nm and a blue shift of the 672 mn band was observed. In the em ission spectrum deconvoluted into Gaussian bands, the major fluorescen ce band referred to as F682 was most susceptible to photodegradation: (1) At all temperatures F682 was blue shifted with respect to the cont rol. (2) The half-width of F682 was temperature independent at T < 10 K and became significantly increased in damaged samples. (3) The tempe rature dependence of Gamma(F682) in the range of 10 K < T < 270 K was less pronounced in damaged samples. Our results support the idea of a multistep model of photodegradation with several intermediates in the pathway from the undamaged control into strongly damaged complexes. Th e temperature dependence of Gamma(F682) is explained by contributions owing to static and dynamical inhomogeneous broadening. The static inh omogeneous broadening increases with progressing degradation. Furtherm ore, our results suggest that aerobic photodegradation of the D1/D2/cy t b559 complexes also causes modifications of the electron-phonon inte ractions. The frequency of the phonon mode dominating the electron pho non coupling decreases in damaged samples.