IRON-SULFUR COMPONENTS OF SUCCINATE-DEHYDROGENASE - STOICHIOMETRY AND KINETIC-BEHAVIOR IN ACTIVATED PREPARATIONS
IRON-SULFUR COMPONENTS OF SUCCINATE-DEHYDROGENASE - STOICHIOMETRY AND KINETIC-BEHAVIOR IN ACTIVATED PREPARATIONS
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DOI：
10.1111/j.1432-1033.1975.tb04128.x
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发表时间：
1975-01-01
期刊：
影响因子：
--
通讯作者：
SINGER, TP
中科院分区：
文献类型：
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作者：
BEINERT, H;ACKRELL, BAC;SINGER, TP
用电子顺磁共振（EPR）技术研究了6 ~ 97 K下广泛或完全活化的牛心琥珀酸脱氢酶制剂。用连二亚硫酸盐进行还原滴定，并对各种类型的可溶性和膜结合酶制剂进行快速动力学研究。检测到以下组分并分析它们的行为：自由基，推测由还原时共价结合的黄素产生，铁氧还蛋白类型的两个铁硫中心，其信号出现在还原时，以及高电位铁硫组分，在氧化状态下可检测到。仅在复合物II和内膜制剂中检测到高电位组分。该组分和其中一个铁氧还蛋白型中心以接近黄素化学计量的量存在，并被底物还原。另一个铁氧还蛋白型中心的存在量是黄素的0.1至0.5倍，并且仅被连二亚硫酸盐还原。琥珀酸盐还原的成分。然而，只有一小部分（高达50%的高电位铁硫中心和40-60%的铁氧还蛋白型铁硫中心）在酶的周转时间内被还原。在络合物II中，任何时候都不超过约10%的黄素以半醌形式出现。可溶性的纯化制剂表现相似，除了高电位组分几乎或完全不存在，并且在滴定和动力学实验中发生自由基的广泛积累（高达70 - 80%的黄素）。在半醌形成速率和底物对铁氧还蛋白型或高电位中心的还原速率之间未观察到显著差异。此外，在这项工作中研究的性质没有定性的差异变得明显的制剂之间含有4或8个铁原子，分别。
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 ferredoxin‐type centers were present in amounts close to stoichiometric with the flavin and were reduced by substrate. The other ferredoxin‐type 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 ferredoxin‐type 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 ferredoxin‐type 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.