Tricarboxylic acid cycle reactants

Many instances of stereospecific selection of enantiotopic groups or faces may be found in nature. One such is extracted from the tricarboxylic acid cycle and is shown in Exercise 1.6. At each step, achiral reactants are transformed to achiral products with high stereospecificity ... 

Free Enekgt Data for the Steps of the Tricarboxylic Acid Cycle and Associated Reactions (25°C. AF values are for unit activity. AF values are for 0.2 atin. Oi, 0.05 atm. CO2, pH 7, and 0.01 M concentration of other reactants. The reactions involving CoA are written ignoring any ions or H2O molecules.)... 

The sequence of events known as the Krebs cycle is indeed a cycle ox-aloacetate is both the first reactant and the final product of the metabolic pathway (creating a loop). Because the Krebs cycle is responsible for the ultimate oxidation of metabolic intermediates produced during the metabolism of fats, proteins, and carbohydrates, it is the central mechanism for metabolism in the cell. In the first reaction of the cycle, acetyl CoA condenses with oxaloacetate to form citric acid. Acetyl CoA utilized in this way by the cycle has been produced either via the oxidation of fatty acids, the breakdown of certain amino acids, or the oxidative decarboxylation of pyruvate (a product of glycolysis). The citric acid produced by the condensation of acetyl CoA and oxaloacetate is a tricarboxylic acid containing three car-boxylate groups. (Hence, the Krebs cycle is also referred to as the citric acid cycle or tricarboxyfic acid cycle.)... 

Acetyl CoA next enters the citric acid cycle, also called the tricarboxylic acid (TCA) cycle, or Krebs cycle. The overall result of the cycle is the conversion of an acetyl group into two molecules of CO2 plus reduced coenzymes by an eight-step sequence. The cycle is a closed loop of reactions in which the product of the final step (oxaloacetate) is a reactant in the first step. The intermediates are constantly regenerated and flow continuously through the cycle, which operates as long as the oxidizing coenzymes NAD" " and FAD are available. 

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