Talbot Darren A, Brand Martin D
MRC Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, UK.
Biochim Biophys Acta. 2005 Sep 5;1709(2):150-6. doi: 10.1016/j.bbabio.2005.07.001.
Mitochondrial uncoupling proteins only catalyse proton transport when they are activated. Activators include superoxide and reactive alkenals, suggesting new physiological functions for UCP2 and UCP3: their activation by superoxide when protonmotive force is high causes mild uncoupling, which lowers protonmotive force and attenuates superoxide generation by the electron transport chain. This feedback loop acts to prevent excessive mitochondrial superoxide production. Superoxide inactivates aconitase in the mitochondrial matrix, so aconitase activity provides a sensitive measure of the effects of UCPs on matrix superoxide. We find that inhibition of UCP3 in isolated skeletal muscle mitochondria by GDP decreases aconitase activity by 25% after 20 min incubation. The GDP effect is absent in skeletal muscle mitochondria from UCP3 knockout mice, showing that it is mediated by UCP3. Protection of aconitase by UCP3 in the absence of nucleotides does not require added fatty acids. The purine nucleoside diphosphates and triphosphates cause aconitase inactivation, but the monophosphates and CDP do not, consistent with the known nucleotide specificity of UCP3. The IC(50) for GDP is about 100 microM. These findings support the proposal that UCP3 attenuates endogenous radical production by the mitochondrial electron transport chain at high protonmotive force.
线粒体解偶联蛋白只有在被激活时才催化质子转运。激活剂包括超氧化物和活性烯醛，这表明UCP2和UCP3具有新的生理功能：当质子动力势较高时，它们被超氧化物激活会导致轻度解偶联，从而降低质子动力势并减弱电子传递链产生的超氧化物。这种反馈回路的作用是防止线粒体过度产生超氧化物。超氧化物会使线粒体基质中的乌头酸酶失活，因此乌头酸酶活性可作为衡量解偶联蛋白对基质超氧化物影响的敏感指标。我们发现，在分离的骨骼肌线粒体中，GDP对UCP3的抑制作用在孵育20分钟后会使乌头酸酶活性降低25%。在UCP3基因敲除小鼠的骨骼肌线粒体中不存在GDP的这种作用，表明它是由UCP3介导的。在没有核苷酸的情况下，UCP3对乌头酸酶的保护作用不需要添加脂肪酸。嘌呤核苷二磷酸和三磷酸会导致乌头酸酶失活，但单磷酸和CDP则不会，这与UCP3已知的核苷酸特异性一致。GDP的IC(50)约为100微摩尔。这些发现支持了这样的观点，即UCP3在高质子动力势下可减弱线粒体电子传递链产生的内源性自由基。
