Study on metabolic control function of adenylate kinase

腺苷酸激酶有助于细胞腺嘌呤核苷酸组成的稳态。已确定三种同工酶：胞质型AK 1，线粒体膜间型AK 2和线粒体基质型AK 3。然而，这种不同的亚细胞分布的生理意义仍然有待解决，本研究旨在分析的影响，在亚细胞分布的酶的细胞代谢后，引入和表达的腺苷酸激酶同工酶的cDNA。为了控制酶的亚细胞分布，对细胞区室特别是线粒体的靶向信号的了解是必不可少的。这项研究确定AK 3分子没有在其他线粒体蛋白中发现的可切割的N-末端序列。当AK 3 cDNA在大肠杆菌中表达时，AK 3蛋白通过细菌内膜输出到周质空间。构建表达质粒，其指导由AK 3的N-末端部分（残基6 - 23）和β-内酰胺酶组成的融合蛋白。将该质粒在E.在大肠杆菌中，融合蛋白在周质中回收。这些结果表明AK 3的N-末端序列参与靶向线粒体基质。

Adenylate kinase contributes to homeostasis of the cellular adenine nucleotide composition. Three isozymes have been identified: the cytosol type-AK1, the mitochondrial intermembraneous-type AK2, and the mitochondrial matrix type-AK3. However, the physiological significance of such different subcellular distribution remains to be solved.This study aims at the analysis of the effect of changes in the subcellular distribution of the enzymes on the cellular metabolism after introduction and expression of cDNAs for adenylate kinase isozymes. To control the subcellular distribution of the enzymes, knowledge on the targeting signal to cellular compartments especially to mitochondria is essential. This study established that the AK3 molecule has no cleavable N-terminal sequence as found in other mitochondrial proteins. When the AK3 cDNA was expressed in Escherichia coli, the AK3 protein was exported to the periplasmic space through the bacterial inner membrane. An expression plasmid was constructed which directs a fusion protein consisting of the N-terminal portion of AK3 (residues 6 - 23) and beta- lactamase. When this plasmid was expressed in E. coli, the fusion protein was recovered in the periplasm. These results indicate that the involvement of the N-terminal sequence of AK3 in targeting to the mitochondrial matrix.