Passarella S, Marra E, Atlante A, Barile M, Doonan S, Quagliariello E
Dipartimento di Biochimica e Biologia Molecolare, Universitá degli Studi Bari, Italy.
Biochim Biophys Acta. 1990 Mar;1022(3):273-82. doi: 10.1016/0005-2736(90)90274-r.
Incubation of intact mitochondria with aspartate aminotransferase results in efflux of malate dehydrogenase and vice versa. The export process is specific and rapid. It shows saturation kinetics with respect to the effector enzyme consistent with involvement of a receptor for the effector in the mitochondrial membrane system. Export is inhibited by both beta-mercaptoethanol and by the metal chelating agent bathophenanthroline; both substances inhibit release of malate dehydrogenase by aspartate aminotransferase competitively whereas for release of aspartate aminotransferase by malate dehydrogenase inhibition is non-competitive. The efflux process is dependent on a trans-membrane pH gradient. Exported enzymes differ from the native forms in their dependence of activity on pH. Export of both aspartate aminotransferase and malate dehydrogenase is effected by incubation of mitochondria with the newly-synthesised precursor of aspartate aminotransferase; this observation provides supporting evidence for the physiological significance of the other results reported here. It is speculated that exported enzymes are on a pathway to degradation, and that coupled uptake and export is involved in the co-ordination of synthesis and breakdown of mitochondrial proteins.
完整的线粒体与天冬氨酸转氨酶一起温育会导致苹果酸脱氢酶外流，反之亦然。这种输出过程具有特异性且迅速。它显示出针对效应酶的饱和动力学，这与效应器的受体参与线粒体膜系统的情况一致。β-巯基乙醇和金属螯合剂邻二氮杂菲均会抑制输出；这两种物质都竞争性地抑制天冬氨酸转氨酶导致的苹果酸脱氢酶释放，而对于苹果酸脱氢酶导致的天冬氨酸转氨酶释放，抑制作用是非竞争性的。外流过程依赖于跨膜pH梯度。输出的酶在活性对pH的依赖性方面与天然形式不同。将线粒体与新合成的天冬氨酸转氨酶前体一起温育会导致天冬氨酸转氨酶和苹果酸脱氢酶的输出；这一观察结果为本文报道的其他结果的生理意义提供了支持性证据。据推测，输出的酶正处于降解途径中，并且耦合的摄取和输出参与线粒体蛋白质合成与分解的协调。
