Indiveri C, Tonazzi A, Palmieri F
Department of Pharmaco-Biology, University of Bari, Italy.
Biochim Biophys Acta. 1994 Jan 3;1189(1):65-73. doi: 10.1016/0005-2736(94)90281-x.
The transport mechanism of the reconstituted carnitine carrier purified from rat liver mitochondria was investigated kinetically. The half-saturation constant (Km) for carnitine on the internal side of the liposomal membrane (8.7 mM) was found to be much higher than that determined for the external surface (0.45 mM). The exclusive presence of a single transport affinity for carnitine on each side of the membrane indicated a unidirectional insertion of the carnitine carrier into the proteoliposomes, most probably right-side-out with respect to mitochondria. Under these defined conditions bisubstrate initial velocity studies of homologous (carnitine/carnitine) and heterologous (carnitine/acylcarnitine) antiport were performed by varying both the internal and external substrate concentrations. The kinetic patterns obtained showed that the ratio Km/Vmax is not influenced by the second (non-varied) substrate, which indicates a ping-pong mechanism. The carnitine carrier thus differs from all other mitochondrial carriers analyzed so far in the reconstituted state, for which a common sequential type of reaction mechanism has been found.
对从大鼠肝脏线粒体中纯化得到的重组肉碱载体的转运机制进行了动力学研究。发现脂质体膜内侧肉碱的半饱和常数（Km）（8.7 mM）远高于外侧测定的值（0.45 mM）。膜两侧对肉碱仅存在单一的转运亲和力，这表明肉碱载体单向插入到蛋白脂质体中，很可能相对于线粒体是外翻的。在这些特定条件下，通过改变内部和外部底物浓度，对同源（肉碱/肉碱）和异源（肉碱/酰基肉碱）反向转运进行了双底物初速度研究。所获得的动力学模式表明，Km/Vmax比值不受第二种（未变化的）底物的影响，这表明是乒乓机制。因此，肉碱载体与目前分析的所有其他处于重组状态的线粒体载体不同，迄今已发现后者具有共同的顺序反应机制类型。
