Brand Martin D, Turner Nigel, Ocloo Augustine, Else Paul L, Hulbert A J
MRC Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, UK.
Biochem J. 2003 Dec 15;376(Pt 3):741-8. doi: 10.1042/BJ20030984.
The proton conductance of isolated liver mitochondria correlates significantly with body mass in mammals, but not in ectotherms. To establish whether the correlation in mammals is general for endotherms or mammal-specific, we measured proton conductance in mitochondria from birds, the other main group of endotherms, using birds varying in mass over a wide range (nearly 3000-fold), from 13 g zebra finches to 35 kg emus. Respiratory control ratios were higher in mitochondria from larger birds. Mitochondrial proton conductance in liver mitochondria from birds correlated strongly with body mass [respiration rate per mg of protein driving proton leak at 170 mV being 44.7 times (body mass in g)(-0.19)], thus suggesting a general relationship between body mass and proton conductance in endotherms. Mitochondria from larger birds had the same or perhaps greater surface area per mg of protein than mitochondria from smaller birds. Hence, the lower proton conductance was caused not by surface area changes but by some change in the properties of the inner membrane. Liver mitochondria from larger birds had phospholipid fatty acyl chains that were less polyunsaturated and more monounsaturated when compared with those from smaller birds. Phospholipid fatty acyl polyunsaturation correlated positively and monounsaturation correlated negatively with proton conductance. These correlations echo those seen in mammalian liver mitochondria, suggesting that they too are general for endotherms.
在哺乳动物中，分离的肝脏线粒体的质子传导率与体重显著相关，但在变温动物中并非如此。为了确定哺乳动物中的这种相关性是恒温动物普遍存在的还是哺乳动物特有的，我们测量了鸟类（另一主要恒温动物类群）线粒体中的质子传导率，所用鸟类体重范围很广（近3000倍），从13克的斑胸草雀到35千克的鸸鹋。较大鸟类线粒体的呼吸控制率更高。鸟类肝脏线粒体中的质子传导率与体重密切相关[在170毫伏驱动质子泄漏时，每毫克蛋白质的呼吸速率为44.7倍（体重，单位为克）（-0.19）]，因此表明恒温动物的体重与质子传导率之间存在普遍关系。较大鸟类的线粒体每毫克蛋白质的表面积与较小鸟类的线粒体相同或可能更大。因此，较低的质子传导率不是由表面积变化引起的，而是由内膜性质的某些变化引起的。与较小鸟类相比，较大鸟类的肝脏线粒体的磷脂脂肪酰链多不饱和程度较低，单不饱和程度较高。磷脂脂肪酰多不饱和程度与质子传导率呈正相关，单不饱和程度与质子传导率呈负相关。这些相关性与在哺乳动物肝脏线粒体中观察到的情况相似，表明它们在恒温动物中也是普遍存在的。
