Kabir F, Wilson J E
Department of Biochemistry, Michigan State University, East Lansing 48824.
Arch Biochem Biophys. 1993 Feb 1;300(2):641-50. doi: 10.1006/abbi.1993.1089.
Approximately 90% of the hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) activity was solubilized by treatment of rat brain mitochondria with glucose 6-phosphate (Glc-6-P), while only about 20% of the hexokinase could be solubilized from human brain mitochondria. Intermediate amounts of solubilized activity were obtained with brain mitochondria from other species. In contrast, > or = 80% of the activity could be released by 0.5 M potassium thiocyanate (KSCN), regardless of the species from which the mitochondria were obtained. Hexokinase activities solubilized by treatment of bovine brain mitochondria with Glc-6-P (HKG6P) and by a subsequent treatment with KSCN (HKKSCN) were indistinguishable in their isoelectric focusing pattern and molecular weight, and both were inhibited by Glc-6-P with Ki approximately 20 microM. Both HKG6P and HKKSCN could bind to mitochondria from rat liver or brain, and both were again solubilized by a subsequent treatment with Glc-6-P. These results do not suggest any intrinsic molecular difference between HKG6P and HKKSCN. Rather, the difference in susceptibility to release by Glc-6-P is reasonably attributed to discrete types of binding sites for hexokinase on brain mitochondria, with the relative proportion of these varying with species. Bovine brain mitochondria bearing HKG6P and HKKSCN were not resolved by sucrose density gradient fractionation, suggesting that both forms may coexist on the same mitochondrion. Given the probable importance of mitochondrially bound hexokinase in regulating aerobic glycolysis in brain, these differences in hexokinase-mitochondrial interactions may be related to previously documented differences in cerebral energy metabolism of these various species.
用6-磷酸葡萄糖（Glc-6-P）处理大鼠脑线粒体后，约90%的己糖激酶（ATP：D-己糖6-磷酸转移酶，EC 2.7.1.1）活性可被溶解，而从人脑海线粒体中只能溶解约20%的己糖激酶。用其他物种的脑线粒体可获得中等量的溶解活性。相比之下，无论线粒体来自何种物种，0.5 M硫氰酸钾（KSCN）均可释放≥80%的活性。用Glc-6-P处理牛脑线粒体后溶解的己糖激酶活性（HKG6P）以及随后用KSCN处理后溶解的己糖激酶活性（HKKSCN），在等电聚焦图谱和分子量方面无明显差异，且二者均受到Glc-6-P的抑制，抑制常数Ki约为20 μM。HKG6P和HKKSCN均可与大鼠肝脏或脑的线粒体结合，随后用Glc-6-P处理后二者又均可被溶解。这些结果并未表明HKG6P和HKKSCN之间存在任何内在分子差异。相反，Glc-6-P对释放的敏感性差异合理地归因于脑线粒体上己糖激酶的不同类型结合位点，这些位点的相对比例因物种而异。携带HKG6P和HKKSCN的牛脑线粒体不能通过蔗糖密度梯度分级分离来区分，这表明两种形式可能共存于同一线粒体上。鉴于线粒体结合的己糖激酶在调节脑内有氧糖酵解中可能具有重要作用，这些己糖激酶与线粒体相互作用的差异可能与先前记录的这些不同物种脑能量代谢的差异有关。
