Proton translocation by the cytochrome bc(1) complexes of phototrophic bacteria: introducing the activated Q-cycle

Mulkidjanian, A.Y.

Автор: Mulkidjanian Armen Y.
Журнал: Photochemical and Photobiological Sciences
Том: 6
Номер: 1
Год издания: 2007
Издательство: Royal Society of Chemistry
Местоположение издательства: United Kingdom
Первая страница: 19
Последняя страница: 34
DOI: 10.1039/b517522d
Аннотация: The cytochrome b(C1) complexes are proton-translocating, dimeric membrane ubiquinol: cytochrome c oxidoreductases that serve as "hubs" in the vast majority of electron transfer chains. After each ubiquinol molecule is oxidized in the catalytic center P at the positively charged membrane side, the two liberated electrons head out, according to the Mitchell's Q-cycle mechanism, to different acceptors. One is taken by the [2Fe-2S] iron-sulfur Rieske protein to be passed further to cytochrome c(1). The other electron goes across the membrane, via the low- and high-potential hemes of cytochrome b, to another ubiquinone-binding site N at the opposite membrane side. It has been assumed that two ubiquinol molecules have to be oxidized by center P to yield first a semiquinone in center N and then to reduce this semiquinone to ubiquinol. This review is focused on the operation of cytochrome b(C1) complexes in phototrophic purple bacteria. Their membranes provide a unique system where the generation of membrane voltage by light-driven, energy-converting enzymes can be traced via spectral shifts of native carotenoids and correlated with the electron and proton transfer reactions. An "activated Q-cycle" is proposed as a novel mechanism that is consistent with the available experimental data on the electron/proton coupling. Under physiological conditions, the dimeric cytochrome b(C1) complex is suggested to be continually primed by prompt oxidation of membrane ubiquinol via center N yielding a bound semiquinone in this center and a reduced, high-potential heme b in the other monomer of the enzyme. Then the oxidation of each ubiquinol molecule in center P is followed by ubiquinol formation in center N, proton translocation and generation of membrane voltage.
Добавил в систему: Мулкиджанян Армен Яковлевич

	ИСТИНА	Войти в систему Регистрация
	ИСТИНА ПсковГУ
	Главная Поиск Статистика О проекте Помощь

ИСТИНА

ИСТИНА ПсковГУ

Proton translocation by the cytochrome bc(1) complexes of phototrophic bacteria: introducing the activated Q-cycleстатья