Marra E, Passarella S, Casamassima E, Perlino E, Doonan S, Quagliariello E
Biochem J. 1985 Jun 1;228(2):493-503. doi: 10.1042/bj2280493.
Kinetic measurements of the uptake of native mitochondrial aspartate aminotransferase and malate dehydrogenase into mitochondria in vitro were carried out. The uptake of both the enzymes is essentially complete in 1 min and shows saturation characteristics. The rate of uptake of aspartate aminotransferase into mitochondria is decreased by malate dehydrogenase, and vice versa. The inhibition is exerted by isoenzyme remaining outside the mitochondria rather than by isoenzyme that has been imported. The thiol compound beta-mercaptoethanol decreases the rate of uptake of the tested enzymes; inhibition is a result of interaction of beta-mercaptoethanol with the mitochondria and not with the enzymes themselves. The rate of uptake of aspartate aminotransferase is inhibited non-competitively by malate dehydrogenase, but competitively by beta-mercaptoethanol. The rate of uptake of malate dehydrogenase is inhibited non-competitively by aspartate aminotransferase and by beta-mercaptoethanol. beta-Mercaptoethanol prevents the inhibition of the rate of uptake of malate dehydrogenase by aspartate aminotransferase. These results are interpreted in terms of a model system in which the two isoenzymes have separate but interacting binding sites within a receptor in the mitochondrial membrane system.
对天然线粒体天冬氨酸转氨酶和苹果酸脱氢酶体外进入线粒体的动力学进行了测定。两种酶的摄取在1分钟内基本完成，并呈现饱和特性。天冬氨酸转氨酶进入线粒体的摄取速率会因苹果酸脱氢酶而降低，反之亦然。抑制作用是由线粒体外剩余的同工酶施加的，而不是由已导入的同工酶施加的。硫醇化合物β-巯基乙醇降低了受试酶的摄取速率；抑制作用是β-巯基乙醇与线粒体相互作用的结果，而非与酶本身相互作用的结果。天冬氨酸转氨酶的摄取速率受到苹果酸脱氢酶的非竞争性抑制，但受到β-巯基乙醇的竞争性抑制。苹果酸脱氢酶的摄取速率受到天冬氨酸转氨酶和β-巯基乙醇的非竞争性抑制。β-巯基乙醇可防止天冬氨酸转氨酶对苹果酸脱氢酶摄取速率的抑制。这些结果是根据一个模型系统来解释的，在该模型系统中，两种同工酶在线粒体膜系统中的一个受体内具有独立但相互作用的结合位点。
