Pande S V, Parvin R
J Biol Chem. 1980 Apr 10;255(7):2994-3001.
Besides carnitine-acylcarnitine translocase-catalyzed exchange diffusions, a relatively much slower unidirectional transport of carnitines also proceeds in mitochondria. The latter proceeds in the direction of the concentration gradient of carnitines and leads to the equilibration of carnitine concentration across the inner membrane. The same translocase that catalyzes exchange diffusion appears to catalyze unidirectional transport inasmuch as the two processes showed similar substrate specificity, sensitivity to inhibitors, high temperature coefficients, apparent affinity for carnitine, and a lack of energy requirement. The unidirectionally imported carnitine readily exchanged against medium carnitine, indicating that the two transport processes share the same pool of mitochondrial carnitine. Unidirectional transport appears to be functional in vivo; its operation seems not only to allow mitochondria to acquire carnitine but to adjust the rates of their faster exchange-diffusion reactions with changes in total tissue carnitine concentrations. The carnitine-acylcarnitine translocase was found to be about 15 times as active in mitochondria of rat liver as in those of heart.
除了肉碱-脂酰肉碱转位酶催化的交换扩散外，肉碱在 mitochondria 中还进行相对较慢的单向转运。后者沿着肉碱的浓度梯度方向进行，导致内膜两侧肉碱浓度达到平衡。催化交换扩散的同一转位酶似乎也催化单向转运，因为这两个过程表现出相似的底物特异性、对抑制剂的敏感性、高温度系数、对肉碱的表观亲和力以及缺乏能量需求。单向导入的肉碱很容易与培养基中的肉碱进行交换，这表明这两个转运过程共享线粒体肉碱的同一池。单向转运在体内似乎是有功能的；其运作似乎不仅使 mitochondria 能够获取肉碱，而且能随着组织总肉碱浓度的变化调整其更快的交换扩散反应速率。发现肉碱-脂酰肉碱转位酶在大鼠肝脏 mitochondria 中的活性约为心脏 mitochondria 中的 15 倍。
