Effect of Carotenoid Composition on Stability and Light-Induced Oxidative Damage of the LH2 Complexes Isolated from Ectothiorhodospira haloalkaliphila

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Earlier, it has been shown that carotenoid-dependent singlet oxygen photogeneration in LH2 of Ectothiorhodospira haloalkaliphila leads to damage to pigments and protein. Present work continues this investigation using LH2 complexes with altered carotenoid composition: carotenoid-less LH2, and LH2 complexes with incorporated neurosporene, spheroidene, or rhodopin (LH2-Neu, LH2-Sph, or LH2-Rho, respectively). This work provides the first data on the products (hydroperoxides of organic molecules, most likely components of the protein matrix of the complexes) of the interaction of singlet oxygen with LH2 components with a modified carotenoid composition; the ability of various carotenoids to both influence the stability of LH2 and participate in oxidative damage to the complexes is assessed. It was shown that inhibition of carotenoid synthesis led to a decrease in LH2 thermal stability and reduced the light-induced oxidative damage to bacteriochlorophyll and protein. Re-incorporation of exogenous carotenoids did not return stability of the complexes but reduced the tendency of complexes to aggregate, and (in the case of LH2-Rho) reactivated both photooxidation of bacteriochlorophyll and photoproduction of organic hydroperoxides. It was concluded that carotenoids play an important role in comple x stability and are capable of inducing oxidative damage to LH2 components through singlet oxygen photogeneration.