Bacteriochlorophyll interaction with singlet oxygen in membranes of purple photosynthetic bacteria: does the protective function of carotenoids exist?

Abstract

Изучено прямое действие синглетного кислорода на бактериохлорофилл (БХл) светособирающих комплексов в мембранах четырех видов пурпурных несерных и серных фотосинтезирующих бактерий с каротиноидами и без каротиноидов. Установлено, что БХл в образцах без каротиноидов, как правило, более устойчив к действию синглетного кислорода по сравнению с контролем. Предполагается, что каротиноиды не нужны для защиты БХл светособирающих комплексов бактерий от синглетного кислорода, а в классической работе Griffith et al.[1] процесс апоптоза клеток бескаротиноидных мутантов, который включает разрушение комплексов, появление мономерного БХл и генерацию последним синглетного кислорода с последующим окислением самого БХл, был ошибочно приписан защитной функции каротиноидов.Ключевые слова: бактериохлорофилл, каротиноиды, синглетный кислород, светособирающие комплексы, бенгальский розовый Presented by Academician of the RAS V.A. ShuvalovThe direct action of singlet oxygen on the bacteriochlorophyll (BChl) of light-harvesting complexes in the membranes of four types of purple non-sulfur and sulfur photosynthesizing bacteria with and without carotenoids has been studied. It has been found that BChl in carotenoid-less samples is generally more resistant to the action of singlet oxygen compared to the control. It is assumed that carotenoids are not needed to protect BChl of bacterial light-harvesting complexes from singlet oxygen, and in the classic work of Griffith et al.[1] the apoptosis process in carotenoid-less mutant cells, which involves the destruction of complexes, the appearance of monomeric BChl and generation of singlet oxygencaused by BChl, followed by BChl oxidation, was mistakenly attributed to the protective function of carotenoids

Carotenoids Do Not Protect Bacteriochlorophylls in Isolated Light-Harvesting LH2 Complexes of Photosynthetic Bacteria from Destructive Interactions with Singlet Oxygen

“…It can only be assumed that the removal of the carotenoid from their structure causes some changes in the latter, which complicates the access of singlet oxygen to BChl. These data coincide with the results of our work on carotenoidless samples of membranes from three types of bacteria [ 23 , 30 ]. In turn, they contradict the hypothesis of a protective role of carotenoids.…”

“…These data are in good agreement with our earlier results, which showed that BChl in the membranes of the carotenoid-free mutant Rba . sphaeroides R26.1 is more resistant to the action of singlet oxygen than BChl in control membranes with carotenoids [ 30 ]. Thus, based on these results, we can make the rather reasonable speculation that carotenoids in this case are not required to protect BChl from oxidation by singlet oxygen in LH complexes.…”

“…The addition of RB as a source of singlet oxygen to this system makes it possible to study the effect of the latter on the spectral characteristics of complexes, as well as to study other related processes. Earlier, we showed that singlet oxygen can diffuse into LH complexes in the membranes of purple bacteria, where it interacts with BChl and oxidizes the latter [ 30 ]. This scheme also works in the case of the LH2 complexes with carotenoids, in which BChl, depending on the type of bacteria, is oxidized with different efficiencies by singlet oxygen.…”

“…We previously confirmed that BChl oxidation in the membranes of Rba . sphaeroides under the influence of light occurs only after the destruction of the LH2 complex and the appearance of monomeric BChl, which can generate singlet oxygen itself in the light [ 30 ]. Thus, our results directly show that carotenoids are not required to protect BChl from the action of singlet oxygen and that, with a decrease in the amount of these pigments in the complex, the resistance of BChl to the action of an oxidant increases.…”