Huszti Z, Magyar K, Keleti J
Department of Pharmacodynamics, Semmelweis Medical School, Budapest, Hungary.
Eur J Biochem. 1991 Apr 10;197(1):191-6. doi: 10.1111/j.1432-1033.1991.tb15898.x.
Activity of crude histidine decarboxylases (HisDC) from the hypothalamus and the lungs, was markedly reduced by incubating with ATP.Mg, cAMP and cAMP-dependent protein kinase A, whereas activity of the crude glandular stomach enzyme changed only slightly under equal condition. The omission of one of these components failed to reduce HisDC activity by as much as the complete system. Addition of bovine heart (type II) or rat cerebellum protein kinase A (types I and II) inhibitor to the assay prevented enzyme inactivation; moreover, protein kinase A inhibitors permitted moderate activation under phosphorylating and control conditions. Cytosolic hypothalamus HisDC activity was elevated 2-2.2-fold by incubating the cytosol for 15 min in the presence of MnCl2, a known stimulator of phosphoprotein phosphatase; this was prevented when 20 mM NaF, a common inhibitor of phosphoprotein phosphatase, was added to the cytosol. The apparent Km of ATP.Mg-treated hypothalamus HisDC for histidine was elevated 5-10-fold compared to controls, whereas the Vmax was approximately the same. Under this condition, the Km was calculated as high as 0.5-2.2 mM (depending on phosphorylating conditions), while controls had a Km of 0.1-0.3 mM (depending on the initial phosphorylating states). Addition of rabbit muscle (type I), bovine heart (type II) or rat cerebellum (types I and II) inhibitor of protein kinase A, to the phosphorylating mixture, abolished the difference in Km between control and ATP.Mg-treated HisDC. Moreover, rat cerebellum protein kinase A inhibitors increased Vmax to above the control level; while 20 mM NaF (inhibitor of phosphoprotein phosphatase) decreased Vmax to approximately one half of that of the controls. These data indicate that HisDC activity in the hypothalamus and the lungs, but not in the stomach, is affected in oppositely by protein kinase A and phosphoprotein phosphatases.
下丘脑和肺中的粗制组氨酸脱羧酶（HisDC）活性，在与ATP·Mg、cAMP和cAMP依赖性蛋白激酶A一起孵育时显著降低，而在相同条件下，粗制腺胃酶的活性仅略有变化。省略这些成分中的任何一种，都不能像完整体系那样大幅降低HisDC活性。向测定体系中添加牛心（II型）或大鼠小脑蛋白激酶A（I型和II型）抑制剂可防止酶失活；此外，蛋白激酶A抑制剂在磷酸化和对照条件下可使酶适度活化。在存在已知的磷蛋白磷酸酶刺激剂MnCl₂的情况下，将下丘脑胞质溶胶孵育15分钟，胞质溶胶中的HisDC活性提高了2至2.2倍；当向胞质溶胶中添加20 mM NaF（一种常见的磷蛋白磷酸酶抑制剂）时，这种情况得到了阻止。与对照相比，经ATP·Mg处理的下丘脑HisDC对组氨酸的表观Km提高了5至10倍，而Vmax大致相同。在这种情况下，Km计算高达0.5至2.2 mM（取决于磷酸化条件），而对照的Km为0.1至0.3 mM（取决于初始磷酸化状态）。向磷酸化混合物中添加兔肌肉（I型）、牛心（II型）或大鼠小脑（I型和II型）蛋白激酶A抑制剂，消除了对照和经ATP·Mg处理的HisDC之间Km的差异。此外，大鼠小脑蛋白激酶A抑制剂使Vmax增加到对照水平以上；而20 mM NaF（磷蛋白磷酸酶抑制剂）使Vmax降低到对照的大约一半。这些数据表明，蛋白激酶A和磷蛋白磷酸酶对下丘脑和肺中的HisDC活性有相反的影响，而对胃中的HisDC活性没有影响。
