DCCD Inhibits the Reactions of the Iron-Sulfur Protein in Rhodobacter sphaeroides Chromatophores
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- 作者：Vladimir P. Shinkarev ; Natalia B. Ugulava ; Antony R. Crofts ; and Colin A. Wraight
- 刊名：Biochemistry
- 出版年：2000
- 出版时间：December 26, 2000
- 年：2000
- 卷：39
- 期：51
- 页码：16206 - 16212
- 全文大小：92K
- 年卷期：v.39,no.51(December 26, 2000)
- ISSN：1520-4995
文摘
N,N'-dicyclohexylcarbodiimide (DCCD) has been reported to inhibit proton translocation bycytochrome bc1 and b6f complexes without significantly altering the rate of electron transport, a processreferred to as decoupling. To understand the possible role of DCCD in inhibiting the protonogenic reactionsof cytochrome bc1 complex, we investigated the effect of DCCD modification on flash-induced electrontransport and electrochromic bandshift of carotenoids in Rb. sphaeroides chromatophores. DCCD hastwo distinct effects on phase III of the electrochromic bandshift of carotenoids reflecting the electrogenicreactions of the bc1 complex. At low concentrations, DCCD increases the magnitude of the electrogenicprocess because of a decrease in the permeability of the membrane, probably through inhibition of FoF1.At higher concentrations (>150 
M), DCCD slows the development of phase III of the electrochromicshift from about 3 ms in control preparations to about 23 ms at 1.2 mM DCCD, without significantlychanging the amplitude. DCCD treatment of chromatophores also slows down the kinetics of flash-inducedreduction of both cytochromes b and c, from 1.5-2 ms in control preparations to 8-10 ms at 0.8 mMDCCD. Parallel slowing of the reduction of both cytochromes indicates that DCCD treatment modifiesthe reaction of QH2 oxidation at the Qo site. Despite the similarity in the kinetics of both cytochromes,the onset of cytochrome c re-reduction is delayed 1-2 ms in comparison to cytochrome b reduction,indicating that DCCD inhibits the delivery of electrons from quinol to heme c1. We conclude that DCCDtreatment of chromatophores leads to modification of the rate of QoH2 oxidation by the iron-sulfur protein(ISP) as well as the donation of electrons from ISP to c1, and we discuss the results in the context of themovement of ISP between the Qo site and cytochrome c1.
M), DCCD slows the development of phase III of the electrochromicshift from about 3 ms in control preparations to about 23 ms at 1.2 mM DCCD, without significantlychanging the amplitude. DCCD treatment of chromatophores also slows down the kinetics of flash-inducedreduction of both cytochromes b and c, from 1.5-2 ms in control preparations to 8-10 ms at 0.8 mMDCCD. Parallel slowing of the reduction of both cytochromes indicates that DCCD treatment modifiesthe reaction of QH2 oxidation at the Qo site. Despite the similarity in the kinetics of both cytochromes,the onset of cytochrome c re-reduction is delayed 1-2 ms in comparison to cytochrome b reduction,indicating that DCCD inhibits the delivery of electrons from quinol to heme c1. We conclude that DCCDtreatment of chromatophores leads to modification of the rate of QoH2 oxidation by the iron-sulfur protein(ISP) as well as the donation of electrons from ISP to c1, and we discuss the results in the context of themovement of ISP between the Qo site and cytochrome c1.