Citric acid cycle control points

The Citric Acid Cycle Is Controlled at Several Points... 

The rate of the citric acid cycle is precisely adjusted to meet an animal cell s needs for ATP (Figure 1718). The primary control points are the allosteric enzymes isocitrate dehydrogenase and a-ketoglutarate dehydrogenase. 

Figure 17.18. Control of the Citric Acid Cycle. The citric acid cycle is regulated primarily by the concentration of ATP and NADH. The key control points are the enzymes isocitrate dehydrogenase and a-ketoglutarate dehydrogenase.

Which of the following reactions is not a control point in the citric acid cycle ... 

FIGURE 19.8 Control points in the conversion of pyruvate to acetyl-CoA and in the citric acid cycle. 

Within the citric acid cycle itself, the three control points are the reactions catalyzed by citrate synthase, isocitrate dehydrogenase, and the a-ketoglutarate dehydrogenase complex. We have already mentioned that the first reaction of the cycle is one in which regulatory control appears, as is to be expected in the first reaction of any pathway. Gitrate synthase is an allosteric enzyme inhibited by ATP, NADH, succinyl-GoA, and its own product, citrate. 

Four control points exist for the citric acid cycle. One, the pyruvate dehydrogenase reaction, lies outside the cycle proper. The formation of citrate and the two oxidative decarboxylations are the other control points. ATP and NADH are inhibitors of the cycle, and ADP and NAD+ are activators. 

How does the pyruvate dehydrogenase reaction control the citric acid cycle There is a control point outside the cycle, the reaction in which pyruvate produces acetyl-GoA. 

How is control exerted within the citric acid cycle Within the citric acid cycle, the three control points are the reactions catalyzed by citrate synthase, isocitrate dehydrogenase, and the a-ketoglutarate dehydrogenase complex. 

Recall Which steps of aerobic metabolism of pyruvate through the citric acid cycle are control points ... 

Indicate the control points of the citric acid cycle and note the activators and inhibitors. 

The rate at which the citric acid cycle operates is precisely adjusted to meet cellular needs for ATP. One important control point is the very first step in the cycle, the synthesis of citrate. The catalyst for this reaction, citrate synthetase, is an allosteric enzyme that is... 

Figure 13.8 Control points in the citric acid cycle.

The microbiostatic action of benzoic acid is based on different inhibition mechanisms, mainly many enzymes in the microbial cell are inhibited (Bosund, 1962 Menon et al., 1990). E.g. in yeast, enzymes that control the acetic acid metabolism and oxidative phosphorylation are inhibited. Benzoic acid appears to intervene at various points in the citric acid cycle, especially that of a-ketoglutaric acid and succinic acid dehydrogenase. Besides its enzyme-inactivating effects, benzoic acid also acts on the cell wall. The types of action of benzoic acid are sometimes very similar to those of sorbic acid, although many more data exist for the latter. 

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