Significance of Mitochondrial Binding and Release of Hexokinase in Metabolic Regulation

1)细胞内的阳离子条件，特别是钾离子和镁离子的浓度，显著地参与了己糖激酶在细胞内的分布。2)己糖激酶与线粒体的结合不仅促进了己糖激动酶的作用，而且还稳定了己糖激动酶。3)几乎是第一次在培养的神经母细胞瘤细胞中检测己糖激酶的细胞内分布，参照研究最广泛的脑组织中的分布。在神经母细胞瘤细胞中，约30%的己糖激酶活性以线粒体结合形式存在。还发现己糖激酶I在细胞中占主导地位，在大脑中也是如此。4)在整个研究过程中，己糖激酶I对有丝分裂键…显示出更高的亲和力胞外葡萄糖浓度变化不大，结合的己糖激酶几乎不变。己糖激酶I的这些特性可能对大脑中葡萄糖代谢的动态平衡很重要。5)在正常大鼠肝脏和再生肝脏中，几乎没有己糖激酶活性与线粒体结合。然而，在一些品系的大鼠腹水肝癌细胞的线粒体中发现了一定程度的己糖激酶活性，这表明己糖激酶在细胞内的分布发生了变化，与致癌有关。6)己糖激酶的翻译后加工被研究，假设加工过程中结合结构域的消除是肝脏中没有线粒体结合的己糖激酶的原因。由于温和的糜蛋白酶处理会导致线粒体结合能力的丧失，而催化活性和相对分子质量变化不大，因此假设己糖激酶分子的N-末端含有丰富的疏水氨基酸结合区域。在肝脏中也发现了类似的活动，但在大脑中没有发现，而且活动集中在肝脏的溶酶体部分。从抑制剂和激活剂的研究中发现，硫醇蛋白水解酶是负责这一过程的。加工活性在一定程度上位于溶酶体的外表面，并对加工的可能机制进行了探讨。较少

Significance of the binding of hexokinase to mitochondria, especially in tissues and cells with high blycolytic activity, was examined with special reference to regulatory mechanism for glucose metabolism.1) Intracellular conditions for cations, especially the concentration of potassium ion in addition to that of magnesium ion, were significantly involved in the intracellular distribution of hexokinase.2) The binding to mitochondria brought about not only the facilitation for the action but also the stabilization of hexokinase.3) Intracellular distridution of hexokinase was also examined for cultured neuroblastoma cells for almost the first time, in reference to that in the brain which has been studied most extenvsively. About 30% of hexokinase activity was found as mitochondria-bound-form in-the neuroblastoma cells. It was also found that hexokinase I was predominant in the cells as was in the brain.4) Throughout the present study, hexokinase I showed much higher affinity to mitochond … More ria than hexokinase II, and the binding hexokinase was almost constant irrespective of the change in extra-cellular concentration of gluose. These properties of hexokinase I may be important for homeo-stasis of glucose metabolism in the brain.5) Almost no hexokinase activity was bound to mitochondria in normal rat liver as well as in the regenerating liver. However, the activity was found to some extent in the mitochondria fraction of some strains of rat ascites hepatoma cells, indicating the change in the intracellular distribution of hexokinase in relation to carcinogenesis.6) Posttranslational processing of hexokinase was investigated on an assumption that the elimination of the binding domain by the processing was responsible for the absence of mitochondria-bound hexokinase in the liver. The binding domain rich in hydrophobic amino acids has been postulated in the n-terminus of hexokinase molecule, since mild chymotrypsin treatment causes loss of the mitochondria-binding ability with little changes in the catalytic activity and molecular weight. Similar activity was found in the liver but not in the brain, and the activity was concentrated in the lysosomal fraction of the liver. From inhibitor and activator studies, thiol protease was found to be responsible for the processing. The processing activity was located in the outer surface of lysosomes to some extent, and possible mechanism for the processing was discussed. Less