HOMOGENEOUS PHOTOBLEACHING OF CHLOROPHYLL HOLOCHROMES IN A PHOTOSYSTEM I REACTION CENTER COMPLEX

Chlorophyll (Chl) photobleaching and P700 photodegradation were followed simultaneously in a P700 Chi a-protein complex (Chl a /P700 < 35). During strong illumination, the photobleaching kinetics of the bulk Chl corresponded with that of P700 photodegradation. The absence of a blue shift of the absorption maximum at 678 nm after photobleaching indicated the simultaneous degradation of all Chl holochromes and the absence of long wavelength-absorbing energy traps that would protect P700 against excess light energy. It was deduced that in the P700 reaction center core complex, the excitons are uniformly distributed amongst the Chl holochromes, which decreases the deleterious effects of excess light energy on P700 and protects the photosystem against photoinhibition.