果糖双磷酸酶-1的别构抑制剂是（）。
A.GDP
B.AMP
C.ATP
D.ADP
E.GTP
参考答案：B
解析：三羧酸循环中唯一的一次底物水平磷酸化是琥珀酰辅酶A生成琥珀酸的反应，琥珀酰辅酶A的高能硫酯链断裂推动GDP的磷酸化，生成GTP。ATP既是磷酸果糖激酶-1的作用底物（低浓度时结合于酶活性中心），又是别构抑制剂（高浓度时结合于活性中心以外的别位），AMP和2，6-二磷酸果糖是磷酸果糖激酶-1的激活剂，同时别构抑制果糖双磷酸酶-1。
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| There are times when people are so tired that they fall asleep almost anywhere. We can see there is a lot of sleeping on the bus or train on the 1 home from work in the evenings. A man will be 2 the newspaper, and seconds later it 3 as if he is trying to 4 it. Or he will fall asleep on the shoulder of the stranger 5 next to him. 6 place where unplanned short sleep 7 is in the lecture hall where a student will start snoring (打鼾) so 8 that the professor has to ask another student to 9 the sleeper awake. A more embarrassing (尴尬) situation occurs when a student starts falling into sleep and the 10 of the head pushes the arm off the 11 , and the movement carries the 12 of the body along. The student wakes up on the floor with no 13 of getting there. The worst time to fall asleep is when 14 . Police reports are full of 15 that occur when people fall into sleep and go 16 the road. If the drivers are 17 , they are not seriously hurt. One woman's car, 18 , went into the river. She woke up in four feet of 19 and thought it was raining. When people are really 20 , nothing will stop them from falling asleep-no matter where they are. | ||||
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