Yokoyama-Sato K, Akimoto H, Imai N, Ishibashi S
Arch Biochem Biophys. 1987 Aug 15;257(1):56-62. doi: 10.1016/0003-9861(87)90542-x.
As a possible mechanism for the absence of mitochondria-bindable hexokinase in the liver, the presence of a protease similar in action to chymotrypsin, which specifically eliminates the binding ability of the bindable hexokinase without changing its catalytic properties, was investigated in rat liver. The lysosomal fraction prepared from the liver converted the bindable hexokinase prepared from rat brain to the nonbindable form with little change in catalytic activity. The activity of such a "processing protease" was much lower in rat brain, where the bindable form is predominant. The processing activity cosedimented with lysosomal marker enzyme activities in the subcellular fractionation of livers from normal and Triton WR-1339-injected rats. A fair portion of the activity was detected in the lysosomes without disruption. The activity was maximal at pH 6.0-7.0, inactivated almost completely by tosylphenylalanine chloromethyl ketone, tosyllysine chloromethyl ketone, leupeptin, antipain, and chymostatin, and dependent on dithiothreitol and mercaptoethanol. These results suggest that a protease, properties of which are fairly similar to those of cathepsin M, may be involved in the post-translational processing of original bindable hexokinase to the nonbindable form in rat liver.
作为肝脏中不存在可与线粒体结合的己糖激酶的一种可能机制，研究人员在大鼠肝脏中调查了一种作用类似于胰凝乳蛋白酶的蛋白酶的存在情况，该蛋白酶能特异性消除可结合己糖激酶的结合能力，而不改变其催化特性。从肝脏制备的溶酶体组分将从大鼠脑制备的可结合己糖激酶转化为不可结合形式，同时催化活性变化不大。在可结合形式占主导的大鼠脑中，这种“加工蛋白酶”的活性要低得多。在正常大鼠和注射曲拉通WR-1339的大鼠肝脏的亚细胞分级分离中，加工活性与溶酶体标记酶活性共沉降。在未破裂的溶酶体中检测到相当一部分活性。该活性在pH 6.0 - 7.0时最大，几乎完全被甲苯磺酰苯丙氨酸氯甲基酮、甲苯磺酰赖氨酸氯甲基酮、亮抑酶肽、抑肽酶和糜蛋白酶抑制素灭活，并依赖于二硫苏糖醇和巯基乙醇。这些结果表明，一种性质与组织蛋白酶M相当相似的蛋白酶可能参与了大鼠肝脏中原始可结合己糖激酶向不可结合形式的翻译后加工过程。
