Weiler U, Riesinger I, Knoll G, Brdiczka D
Biochem Med. 1985 Apr;33(2):223-35. doi: 10.1016/0006-2944(85)90031-6.
A functional coupling between bound hexokinase and the inner mitochondrial compartment has been shown. It is based structurally on the binding of hexokinase to a pore protein which is present in zones of contact between the two boundary membranes. The latter was observed by electron microscopic localization of antiporin and hexokinase at the mitochondrial surface. The four isoenzymes present in liver differ considerably in their activity after binding to the mitochondrial surface. This was found by binding studies using the four isoenzymes isolated from the supernatant. Isoenzyme IV did not bind at all. Isoenzymes I-III did bind and became activated: I, 5.9-fold; II, 39-fold; and III, 1.3-fold. These results suggest that the in vivo activity of hexokinase in the mitochondrial fraction is much larger than so far observed. Furthermore the binding of isoenzymes was differently affected by metabolites. Glucose-6-phosphate exclusively desorbed isoenzyme I from the mitochondrial membrane whereas free fatty acids predominantly liberated isoenzymes II and III. A reciprocal change of the levels of free fatty acids and glucose 6-phosphate in livers of starved rats therefore, can explain why exclusively mitochondrial-bound isoenzymes II and III decreased 10-fold while at the same time isoenzyme I increased.
已证明结合型己糖激酶与线粒体内室之间存在功能偶联。其结构基础是己糖激酶与一种孔蛋白结合，该孔蛋白存在于两个边界膜的接触区域。通过抗孔蛋白和己糖激酶在线粒体表面的电子显微镜定位观察到了后者。肝脏中存在的四种同工酶与线粒体表面结合后，其活性有很大差异。这是通过使用从上清液中分离出的四种同工酶进行结合研究发现的。同工酶IV根本不结合。同工酶I - III确实结合并被激活：I为5.9倍；II为39倍；III为1.3倍。这些结果表明，线粒体部分中己糖激酶的体内活性比迄今为止观察到的要大得多。此外，同工酶的结合受代谢物的影响不同。6 - 磷酸葡萄糖仅使同工酶I从线粒体膜上解吸，而游离脂肪酸主要释放同工酶II和III。因此，饥饿大鼠肝脏中游离脂肪酸和6 - 磷酸葡萄糖水平的相互变化可以解释为什么仅线粒体结合的同工酶II和III减少了10倍，而同时同工酶I增加。
