ULTRAVIOLET-B PHOTODESTRUCTION OF A LIGHT-HARVESTING COMPLEX

Cyanobacteria are important contributors to global photosynthesis in b oth marine and terrestrial environments. Quantitative data are present ed on UV-B-induced damage to the major cyanobacterial photosynthetic l ight harvesting complex, the phycobilisome, and to each of its constit uent phycobiliproteins. The photodestruction quantum yield, Phi(295) n m, for the phycobiliproteins is high (approximate to 10(-3), as compar ed with approximate to 10(-7) for visible light). Energy transfer on a picosecond time scale does not compete with photodestruction. Photoda mage to phycobilisomes in vitro and in living cells is amplified by ca using dissociation and loss of function of the complex. In photosynthe tic organisms, UV-B damage to light-harvesting complexes may significa ntly exceed that to DNA.