Photoinactivation of Microcystis aeruginosa ribulose 1,5-bisphosphate carboxylase: Effects of endogenous and added sensitizers and the role of oxygen

Photoinactivation in vivo of superoxide dismutase and catalase in the cyanobacterium Microcystis aeruginosa

“…Damage to the light reactions of photosynthesis occurs to Photosystem II, at a site on the water-splitting side, close to the reaction centre, whilst Photosystem I activity appears to be unaffected [6,7]. RuBP carboxylase, the CO2-fixing enzyme of photosynthesis, is also inactivated by visible wavelengths under photoinhibitory conditions in vitro and in vivo [2,8,9]. Photoinhibition of Photosystem II in Microcystis 7820 is not increased by elevated 02 tensions, although 02 is required for the photobleaching of chlorophyll [6] and the photoinactivation of RuBP carboxylase [8].…”

“…Photoinhibition of Photosystem II in Microcystis 7820 is not increased by elevated 02 tensions, although 02 is required for the photobleaching of chlorophyll [6] and the photoinactivation of RuBP carboxylase [8]. The role of toxic O 2 species, including singlet oxygen, hydrogen peroxide and superoxide radicals, in photooxidative damage and cell death is well established [2,3,10-12] and these species appear to be involved in the photoinactivation of the cyanobacterial RuBP carboxylase [8,9]. A range ~)f defence mechanisms exist in cyanobacteria, as in other cells, to deactivate the toxic oxygen species.…”