Differential inhibition of the yeast bc(1) complex by phenanthrolines and ferroin - Implications for structure and catalytic mechanism

被引:16
作者
Boumans, H
vanGaalen, MCM
Grivell, LA
Berden, JA
机构
[1] UNIV AMSTERDAM, EC SLATER INST BIOCHEM RES, NL-1018 TV AMSTERDAM, NETHERLANDS
[2] UNIV AMSTERDAM, BIOCTR, DEPT MOL CELL BIOL, MOL BIOL SECT, NL-1018 TV AMSTERDAM, NETHERLANDS
关键词
D O I
10.1074/jbc.272.27.16753
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
o-Phenanthroline and m-phenanthroline both inhibit the electron transfer activity of lauryl maltoside-solubilized yeast be, complex progressively with time, Presteady state kinetics indicate that these compounds bind to the complex on the intermembrane space side, thereby blocking reduction of cytochrome b via the ubiquinol oxidation site, o-Phenanthroline is additionally capable of chelating an iron atom derived from the Rieske Fe-S cluster, thereby distorting the structure of the Rieske protein, EPR analysis shows that the secondary effect of o-phenanthroline occurs after initial inactivation and that m-phenanthroline, which lacks chelating activity, does not affect the Rieske Fe-S cluster, Spectral analysis shows that the b and c(1) cytochromes are still dithionite-reducible after inactivation by o-phenanthroline, indicating that they remain intact, Inactivation by o-phenanthroline can be prevented by the addition of Fe2+, Surprisingly, ferroin, the o-phenanthroline-ferrous sulfate complex, also inhibits the bc(1) complex activity, In contrast to o-phenanthroline, this effect is instantaneous, The two types of inhibition are clearly distinguishable by pre-steady-state reduction kinetics, Interestingly, ferroin can only inhibit electron transfer activity by about 50%, This behavior is discussed in relation to the dimeric structure of the bc(1) complex, and we conclude that ferroin binds to only one of the two protomers, The rate of inactivation by o-phenanthroline is dependent on the incubation temperature and can be quantitated in terms of the half-life for a certain temperature, the time at which the be, activity is reduced to 50%. In contrast to the solubilized form, the bc(1) complex in intact mitochondria is insensitive to o-phenanthroline, suggesting that the inactivation rate by o-phenanthroline is dependent on accessibility of the complex to the agent. Reaction with o-phenanthroline is thus a useful technique for study of structural stability of the bc(1) complex under different conditions and should provide a sensitive tool for determination of the relative stability of mutant enzymes.
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页码:16753 / 16760
页数:8
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