REGULATION OF PENTOSE-PHOSPHATE CYCLE
REGULATION OF PENTOSE-PHOSPHATE CYCLE
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DOI：
10.1042/bj1380425
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发表时间：
1974-01-01
影响因子：
4.1
通讯作者：
KREBS, HA
中科院分区：
文献类型：
--
作者：
EGGLESTON, LV;KREBS, HA
1.研究了可能对大鼠肝脏中葡萄糖6-磷酸脱氢酶反应（氧化戊糖磷酸循环的限速步骤）施加“精细”控制的机制。2.预期葡萄糖6-磷酸脱氢酶反应实际上完成，因为初级产物（6-磷酸葡萄糖酸内酯）被快速水解，并且联合脱氢酶和内酯酶反应的平衡有利于磷酸葡萄糖酸的实际上完全形成。然而，由于葡萄糖6-磷酸脱氢酶被NADPH抑制，反应不会完成（Neglein &哈斯，1935）。3.抑制的测量（其与NADP+竞争）表明，在游离NADP+和游离NADPH的生理浓度下，酶几乎完全被抑制。这表明酶活性的调节是去抑制的问题。4.在超过100种细胞成分中，只有GSSG和AMP抵消了NADPH的抑制作用;只有GSSG在生理上可能发生的浓度下非常有效。5. GSSG的效果不是由于肝提取物的GSSG还原酶活性，因为在测试条件下，这种酶的活性是非常弱的，和完全抑制还原酶的Zn 2+没有取消GSSG的效果。6.在加入葡萄糖6-磷酸和NADPH之前，在Mg ~（2+）和NADP ~+存在下，将酶制剂与GSSG预孵育，大大增加了GSSG效应。7.透析的肝提取物和纯化的葡萄糖6-磷酸脱氢酶废除GSSG的效果，表明在GSSG的行动的辅助因子的参与。8.通过透析或纯化除去的辅因子非常不稳定。通过超滤肝匀浆，可以从葡萄糖6-磷酸脱氢酶中分离出辅因子。余因子的一些性质进行了描述。9. GSSG通过抵消NADPH对葡萄糖6-磷酸脱氢酶的抑制作用来精细控制戊糖磷酸循环的假设进行了讨论。
1. A search was made for mechanisms which may exert a `fine' control of the glucose 6-phosphate dehydrogenase reaction in rat liver, the rate-limiting step of the oxidative pentose phosphate cycle. 2. The glucose 6-phosphate dehydrogenase reaction is expected to go virtually to completion because the primary product (6-phosphogluconate lactone) is rapidly hydrolysed and the equilibrium of the joint dehydrogenase and lactonase reactions is in favour of virtually complete formation of phosphogluconate. However, the reaction does not go to completion, because glucose 6-phosphate dehydrogenase is inhibited by NADPH (Neglein & Haas, 1935). 3. Measurements of the inhibition (which is competitive with NADP+) show that at physiological concentrations of free NADP+and free NADPH the enzyme is almost completely inhibited. This indicates that the regulation of the enzyme activity is a matter of de-inhibition. 4. Among over 100 cell constituents tested only GSSG and AMP counteracted the inhibition by NADPH; only GSSG was highly effective at concentrations that may be taken to occur physiologically. 5. The effect of GSSG was not due to the GSSG reductase activity of liver extracts, because under the test conditions the activity of this enzyme was very weak, and complete inhibition of the reductase by Zn2+did not abolish the GSSG effect. 6. Preincubation of the enzyme preparation with GSSG in the presence of Mg2+and NADP+before the addition of glucose 6-phosphate and NADPH much increased the GSSG effect. 7. Dialysis of liver extracts and purification of glucose 6-phosphate dehydrogenase abolished the GSSG effect, indicating the participation of a cofactor in the action of GSSG. 8. The cofactor removed by dialysis or purification is very unstable. The cofactor could be separated from glucose 6-phosphate dehydrogenase by ultrafiltration of liver homogenates. Some properties of the cofactor are described. 9. The hypothesis that GSSG exerts a fine control of the pentose phosphate cycle by counteracting the NADPH inhibition of glucose 6-phosphate dehydrogenase is discussed.