Murthy M S, Pande S V
J Biol Chem. 1984 Jul 25;259(14):9082-9.
Mitochondrial imports of acylcarnitine and carnitine have been measured by new methods based on the monitoring of deacylation of acylcarnitines and the acetylation of carnitine in the matrix, subsequent to their entry. These methods have shown higher import rates than those calculated from the uptake of radioactive carnitines into mitochondria as employed until presently. This new approach has permitted the import of long chain acylcarnitine to be followed unambiguously; the results have confirmed that the carnitine acylcarnitine translocase is indeed involved in this import which also proceeds by a mole to mole exchange-diffusion against internal carnitine. Depletion of matrix carnitine greatly decreased the substrate import rates based on their uptake assay but much less so when the deacylation and acylation techniques were employed to monitor imports. These results have revealed that there is a small pool of carnitine in the matrix which readily equilibrates with the medium carnitine through the translocase but which equilibrates with the larger matrix carnitine pool slowly. This finding has necessitated reinterpretation of several previous observations on the translocase that were based on the assumption of a single matrix carnitine pool and in which the translocase was assumed to constitute the rate-limiting step in the activity measurements.
基于监测酰基肉碱的脱酰作用以及肉碱进入线粒体基质后的乙酰化作用，已采用新方法对线粒体中酰基肉碱和肉碱的导入进行了测量。这些方法显示出的导入速率高于目前一直采用的通过放射性肉碱摄入线粒体来计算的速率。这种新方法能够明确追踪长链酰基肉碱的导入；结果证实，肉碱-酰基肉碱转位酶确实参与了这种导入过程，该过程也是通过与线粒体内的肉碱进行摩尔对摩尔的交换扩散来进行的。基于摄取分析，线粒体基质中肉碱的耗尽极大地降低了底物的导入速率，但采用脱酰作用和酰化技术监测导入时，降低的幅度要小得多。这些结果表明，线粒体基质中存在一小部分肉碱池，它通过转位酶能迅速与培养基中的肉碱达到平衡，但与更大的线粒体基质肉碱池达到平衡的速度较慢。这一发现使得必须重新解释之前基于单一线粒体基质肉碱池假设对转位酶所做的一些观察结果，在这些观察中，转位酶被认为是活性测量中的限速步骤。
