Glycogen synthesis by rat hepatocytes.
Glycogen synthesis by rat hepatocytes.
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DOI：
10.1042/bj1800389
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发表时间：
1979-05
期刊：
影响因子：
--
通讯作者：
J. Katz;S. Golden;P. Wals
中科院分区：
文献类型：
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作者：
J. Katz;S. Golden;P. Wals
1.来自饥饿大鼠或先前通过根皮苷或胰高血糖素注射耗尽糖原含量的进食大鼠的肝细胞，当与10 mM-葡萄糖、糖原前体（乳酸、甘油、果糖等）孵育时，以快速速率形成糖原。和谷氨酰胺。存在葡萄糖和糖原的净合成。来自所有三种类型底物的14 C被掺入糖原中，但来自葡萄糖的掺入代表碳原子的交换，而不是净掺入。14 C掺入不用于测量来自任何一种底物的净糖原合成。2.以葡萄糖作为唯一底物，净葡萄糖摄取和糖原沉积开始于约12- 15 mM的浓度。糖原合成随葡萄糖浓度的增加而增加，在50- 60 mM时达到最大值，与10 mM葡萄糖和乳酸加谷氨酰胺时的结果相似。3.在糖原合成的同时监测糖原合酶和磷酸化酶的活性（a）和总（a+B）形式的活性。总合酶是不恒定的，在1小时的孵育期。总的活性合成酶活性增加与糖原合成平行。4.糖原磷酸化酶在两个方向上进行测定，通过将1-磷酸葡萄糖转化为糖原和通过糖原的磷酸化。在AMP存在下或在磷酸化酶激酶转化成磷酸化形式后测定总磷酸化酶。对各种方法所得结果进行了比较。虽然通过程序测量的速率不同，但孵育期间的变化模式大致相同。总磷酸化酶不是恒定的。5.活性磷酸化酶和总磷酸化酶的量在洗涤的细胞沉淀中最高。在含氧培养基中孵育，有或无底物，引起活性和总酶的测定量迅速和明显下降。磷酸化酶活性与糖原合成无相关性。与果糖，活性和总磷酸化酶活性增加糖原合成过程中。6.在糖原合成从葡萄糖作为唯一的底物有一个下降，磷酸化酶的活动与葡萄糖浓度的增加和糖原沉积率的增加。这种减少在进食大鼠的细胞中显着。7.为了确定磷酸解和糖原合成是否同时发生，用[2- 3 H，1- 14 C]-半乳糖预标记糖原。在随后的糖原沉积过程中，尽管有大量的可测定的活性磷酸化酶，但糖原的活性没有损失。
1. Hepatocytes from starved rats or fed rats whose glycogen content was previously depleted by phlorrhizin or by glucagon injections, form glycogen at rapid rates when incubated with 10mM-glucose, gluconeogenic precursors (lactate, glycerol, fructose etc.) and glutamine. There is a net synthesis of glucose and glycogen. 14C from all three types of substrate is incorporated into glycogen, but the incorporation from glucose represents exchange of carbon atoms, rather than net incorporation. 14C incorporation does not serve to measure net glycogen synthesis from any one substrate. 2. With glucose as sole substrate net glucose uptake and glycogen deposition commences at concentrations of about 12--15mM. Glycogen synthesis increases with glucose concentrations attaining maximal values at 50--60mM, when it is similar to that obtained in the presence of 10mM glucose and lactate plus glutamine. 3. The activities of the active (a) and total (a+b) forms of glycogen synthase and phosphorylase were monitored concomitant with glycogen synthesis. Total synthase was not constant during a 1 h incubation period. Total and active synthase activity increased in parallel with glycogen synthesis. 4. Glycogen phosphorylase was assayed in two directions, by conversion of glycose 1-phosphate into glycogen and by the phosphorylation of glycogen. Total phosphorylase was assyed in the presence of AMP or after conversion into the phosphorylated form by phosphorylase kinase. Results obtained by the various methods were compared. Although the rates measured by the procedures differ, the pattern of change during incubation was much the same. Total phosphorylase was not constant. 5. The amounts of active and total phosphorylase were highest in the washed cell pellet. Incubation in an oxygenated medium, with or without substrates, caused a prompt and pronounced decline in the assayed amounts of active and total enzyme. There was no correlation between phosphorylase activity and glycogen synthesis from gluconeogenic substrates. With fructose, active and total phosphorylase activities increased during glycogen syntheses. 6. In glycogen synthesis from glucose as sole substrate there was a decline in phosphorylase activities with increased glucose concentration and increased rates of glycogen deposition. The decrease was marked in cells from fed rats. 7. To determine whether phosphorolysis and glycogen synthesis occur concurrently, glycogen was prelabelled with [2-3H,1-14C]-galactose. During subsequent glycogen deposition there was no loss of activity from glycogen in spite of high amounts of assayable active phosphorylase.