Isocitric Succinic dehydrogenase

Enzymes a) citrate synthase b) aconitase c) isocitrate dehydrogenase d) a-oxoglutarate dehydrogenase e) succiny CoA synthetase f) succinate dehydrogenase g) fumarase h) malate dehydrogenase i) nucleoside diphosphokinase. 

Figure 4. The citrate cycle. There is complete oxidation of one molecule of acetyl-CoA for each turn of the cycle CH3COSC0A + 2O2 - 2CO2 + H2O + CoASH. The rate of the citrate cycle is determined by many factors including the ADP/ATP ratio, NAD7NADH ratio, and substrate concentrations. During muscle contraction, Ca is released from cellular stores (mainly the sarcoplasmic reticulum) and then taken up in part by the mitochondria (see Table 2). Ca " activates 2-oxoglutarate and isocitrate dehydrogenases (Brown, 1992). Succinate dehydrogenase may be effectively irreversible. Enzymes ...

Balance Sheet for the Citric Acid Cycle The citric acid cycle has eight enzymes citrate synthase, aconitase, isocitrate dehydrogenase, a-ketoglutarate dehydrogenase, succinyl-CoA synthetase, succinate dehydrogenase, fumarase, and malate dehydrogenase. 

Three modifications of the conventional oxidative citric acid cycle are needed, which substitute irreversible enzyme steps. Succinate dehydrogenase is replaced by fumarate reductase, 2-oxoglutarate dehydrogenase by ferredoxin-dependent 2-oxoglutarate oxidoreductase (2-oxoglutarate synthase), and citrate synthase by ATP-citrate lyase [3, 16] it should be noted that the carboxylases of the cycle catalyze the reductive carboxylation reactions. There are variants of the ATP-driven cleavage of citrate as well as of isocitrate formation [7]. The reductive citric acid... 

There are four major regulatory enzymes in the citric acid cycle. These are citrate synthase (step 1), isocitrate dehydrogenase (step 3), 2-oxoglutarate dehydrogenase (step 4), and succinate dehydrogenase (step 6). 

D. Pyruvate dehydrogenase and a-ketoglutarate dehydrogenase require four vitamins for synthesis of their coenzymes (thiamine, pantothenate, niacin, and riboflavin). Niacin is also required for the NAD+ utilized by isocitrate dehydrogenase and malate dehydrogenase. Riboflavin is required for the FAD utilized by succinate dehydrogenase and the FMN of the electron transport chain. Biotin is not required. 

B. In the conversion of isocitrate (Compound A) to fumarate (Compound B), 2 C02, NADH (which contains niacin), 1 GTP, and 1 FADH2 are produced. A total of approximately 9 ATP are generated. The enzymes for these reactions are all located in the mitochondrial matrix except succinate dehydrogenase, which is in the inner mitochondrial membrane. GTP does not drive any of the reactions. 

The answer is b. (Murray, pp 182-189. Scriver, pp 1521-1552. Sack, pp 121-138. Wilson, pp 287-317.) Reducing equivalents are produced at four sites in the citric acid cycle. NADH is produced by the isocitrate dehydrogenase-catalyzed conversion of a-ketoglutarate to succinyl CoA and by the malate dehydrogenase-catalyzed conversion of malate to oxaloacetate. FADH, is produced by the succinate dehydrogenase-catalyzed conversion of succinate to fumarate. Succinyl CoA synthetase catalyzes the formation of succinate from succinyl CoA, with the concomitant phosphorylation of GDP to GTP... 

Isocitrate Dehydrogenase a Ketoglutarate Dehydrogenase Complex Succinyl-CoA Synthetase Succinate Dehydrogenase... 

Isocitrate Lyase Malate Synthase Succinate Dehydrogenase Fumarate Hydratase (Fumarase)... 

The enzymes of the TCA cycle rely heavily on coenzymes for their catalytic function. Isocitrate dehydrogenase and malate dehydrogenase use NAD as a coenzyme, and succinate dehydrogenase uses FAD. Citrate synthase catalyzes a reaction that uses a CoA derivative, acetyl CoA. The a-ketoglutarate dehydrogenase complex uses thiamine pyrophosphate, lipoate and FAD as bound coenzymes, and NAD and CoASEl as substrates. Each of these coenzymes has unique structural features that enable it to fulfill its role in the TCA cycle. 

Isocitrate dehydrogenase a-Ketoglutarate dehydrogenase Succinyl-CoA synthetase Succinate dehydrogenase Fumarase... 

Two turns of the TCA cycle, with NADH produced at the pyruvate dehydrogenase, isocitrate dehydrogenase, alpha-ketoglutarate, and malate dehydrogenase steps and FADH2 produced at the succinate dehydrogenase step and GTP (equivalent to ATP) produced at the succinyl-coenzyme A synthetase step. 

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