Singlet oxygen formation and chlorophyll a triplet excited state deactivation in the cytochrome b 6 f complex from Bryopsis corticulans

We have attempted to investigate the correlation between the detergent-perturbed structural integrity of the Cyt b 6 f complex from the marine green alga Bryopsis corticulans and its photo-protective properties, for which the nonionic detergents n -octyl-β- d -glucopyranoside (β-OG) and n -dodecyl-β- d -maltoside (β-DM), respectively, were used for the preparation of Cyt b 6 f , and the singlet oxygen ( 1 O 2 *) production as well as the triplet excited-state chlorophyll a ( 3 Chl a *) formation and deactivation were examined by spectroscopic means. Near-infrared luminescence of 1 O 2 * (~1,270 nm) on photo-irradiation was detected for the β-OG preparation where the complex is mainly in oligomeric state, but not for the β-DM one in which the complex exists in dimeric form. Under anaerobic condition, photo-excitation of Chl a in the β-DM preparation generated 3 Chl a * with a lower quantum yield of Φ T ~ 0.02 and a longer lifetime of ~600 μs with respect to those as in the case of β-OG preparation, Φ T ~ 0.12 and 200–300 μs. These results prove that the enzymatically active and intact Cyt b 6 f complex on photo-excitation tends to produce little 3 Chl a * or 1 O 2 * , which implies that the pigment–protein assembly of Cyt b 6 f complex per se is crucial for photo-protection.