TCA cycle enzymes

Complex II is perhaps better known by its other name—succinate dehydrogenase, the only TCA cycle enzyme that is an integral membrane protein in the inner mitochondrial membrane. This enzyme has a mass of approximately 100 to 140 kD and is composed of four subunits two Fe-S proteins of masses 70 kD and 27 kD, and two other peptides of masses 15 kD and 13 kD. Also known as flavoprotein 2 (FP2), it contains an FAD covalently bound to a histidine residue (see Figure 20.15), and three Fe-S centers a 4Fe-4S cluster, a 3Fe-4S cluster, and a 2Fe-2S cluster. When succinate is converted to fumarate in the TCA cycle, concomitant reduction of bound FAD to FADHg occurs in succinate dehydrogenase. This FADHg transfers its electrons immediately to Fe-S centers, which pass them on to UQ. Electron flow from succinate to UQ,... 

Figure 5.3 Major control points of glycolysis and the TCA cycle. Enzymes I, hexokinase II, phosphofructokinase III, pyruvate kinase IV, pyruvate dehydrogenase V, citrate synthase VI, aconitase VII, isocitrate dehydrogenase VIII, a-oxoglutarate dehydrogenase.

MANY TCA CYCLE ENZYMES AND COMPONENTS OF OXIDATIVE PHOSPHORYLATION ARE DIFFERENTIALLY DISTRIBUTED IN NEURONAL AND GLIAL MITOCHONDRIA 545... 

Reactions of the TCA cycle Enzyme that oxidatively decarboxylates pyruvate, its coenzymes, activators, and inhibitors REACTIONS OF THE TRICARBOXYLIC ACID CYCLE (p. 107) Pyruvate is oxidatively decarboxylated by pyruvate dehydrogenase complex producing acetyl CoA, which is the major fuel for the tricarboxylic acid cycle (TCA cycle). The irreversible set of reactions catalyzed by this enzyme complex requires five coenzymes thiamine pyrophosphate, lipoic acid, coenzyme A (which contains the vitamin pantothenic acid), FAD, and NAD. The reaction is activated by NAD, coenzyme A, and pyruvate, and inhibited by ATP, acetyl CoA, and NADH. 

TCA cycle enzyme synthesizing a-ketoglu-tarate, its products, inhibitors, and activators... 

Glutaminase, aspartate aminotransferase, TCA cycle enzymes, citrate lyase, malate dehydrogenase, and NADP+-linked malate enzyme. 

In addition to assays for the OXPHOS enzymes, assays have been described for many other enzymes involved in the MEGS. For PDHc, various types of diagnostic assays have been described and are widely used (33). Also for the TCA cycle enzymes various assays have been described, although to date, pathogenic defects have only been found in a-ketoglutarate dehydrogenase (38), succinate-CoA ligase (12), and fumarase (39). 

Reisch AS, Elpeleg O. Biochemical assays for mitochondrial activity assays of TCA cycle enzymes and PDHc. Methods Cell Biol. 2007 80 199-222. 

C. Velot, M B. Mixon, M. Teige, and P.A. Srere. 1997. Model of a quinary structure between Krebs TCA cycle enzymes A model for the metabolon Biochemistry 36 14271-14276. (PubMed)... 

The TCA cycle is the major final common pathway of oxidation of carbohydrates, lipids, and proteins, since their oxidation yields acetyl-CoA. Acetyl-CoA also serves as precursor in the synthesis of fatty acids, cholesterol, and ketone bodies. All enzymes of the cycle are located in the mitochondrial matrix except for succinate dehydrogenase, which is embedded in the inner mitochondrial membrane. Thus, the reducing equivalents generated in the cycle have easy access to the electron transport chain. TCA cycle enzymes, with the exception of a-ketoglutarate dehydrogenase complex and succinate dehydrogenase, are also present outside the mitochondria. The overall TCA cycle is shown in Figure 13-12. 

TCA cycle substrates oxaloacetate and acetyl-CoA and the product NADH are the critical regulators. The availability of acetyl-CoA is regulated by pyruvate dehydrogenase complex. The TCA cycle enzymes citrate synthase. 

The matrix is viscous and contains all TCA cycle enzymes except succinate dehydrogenase, which is a component of electron transport complex II and is located within... 

A postoperative patient on intravenous fluids develops lesions in the mouth (angular stomatitis). Urinalysis indicates an excretion of 15 pg riboflavin/mg creatinine, which is abnormally low. Which of the following TCA cycle enzymes is most likely to be affected ... 

However, is it possible that malaria parasites also have a functional Krebs cycle Gene expression profiles of blood-stage parasites have indicated an apparent coordinated expression of genes encoding TCA cycle enzymes however, since the expression is so low, it is understandable why biochemical assays failed to detect such activities. (Unexplained is how Speck, Moulder and Evans (1946) were able to detect TCA cycle enzymes.) Since plasmodial mitochondria lack pyruvate kinase the... 

---