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Iron-Sulfur Components of Succinate Dehydrogenase: Stoichiometry and Kinetic Behavior in Activated Preparations.
- Source :
-
European Journal of Biochemistry . May75 Part 2, Vol. 54 Issue 1, p185-194. 10p. - Publication Year :
- 1975
-
Abstract
- Extensively or completely activated preparations of beef heart succinate dehydrogenase have been investigated by electron paramagnetic resonance (EPR) techniques at 6 to 97 K. Reductive titrations with dithionite and rapid kinetic studies were performed with various types of soluble and membrane-bound preparations of the enzyme. The following components were detected and their behavior analyzed: a free radical, presumably arising from the covalently bound flavin on reduction, two iron-sulfur centers of the ferredoxin type, the signals of which appear on reduction, and a high-potential iron-sulfur component, detectable in the oxidized state. The high-potential component was only detected in complex II and inner-membrane preparations. This component and one of the ferredoxin­type centers were present in amounts close to stoichiometric with the flavin and were reduced by substrate. The other ferredoxin­type center was present in amounts between 0.1 and 0.5 times that of the flavin and was reduced only by dithionite. Of the components reduced by succinate, however, only a fraction (up to 50% of the high-potential iron-sulfur center and 40-60% of the ferredoxin­type iron-sulfur center) was reduced within the turnover time of the enzymes, in complex II not more than about 10% of the flavin appeared in the semiquinone form at any time. Soluble, purified preparations behaved similarly except that the high-potential component was nearly or completely absent and extensive accumulation of the free radical occurred (up to 70 to 80% of the flavin) in titration and kinetic experiments. No significant difference was observed between the rates of semiquinone formation and the reduction of the ferredoxin­type or high-potential centers by the substrate. Also no qualitative differences in the properties studied in this work became apparent between preparations containing 4 or 8 iron atoms, respectively. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00142956
- Volume :
- 54
- Issue :
- 1
- Database :
- Academic Search Index
- Journal :
- European Journal of Biochemistry
- Publication Type :
- Academic Journal
- Accession number :
- 12614732
- Full Text :
- https://doi.org/10.1111/j.1432-1033.1975.tb04128.x