2-Ketoglutaric succinate

Fig. 16 a Fluorescence images of intermediates of the Krebs cycle, b Relative fluorescence intensities of the respective EuTc-L complexes at different lag times. The concentration of EuTc is 50 ixrnolL-1, the concentration of the ligands citrate, isocitrate, ketoglutarate, succinate, fumarate, L-malate, and oxaloacetate is 150 imol L 1 throughout. F0 and F are the fluorescence intensities of EuTc and the EuTc-L complex, respectively... 

Figure 5. Schematic diagrams of the sequential labeling of the individual carbon atoms of different intermediates of the citric acid cycle. A shows reactions of acetyl-CoA C-2 (AC2) and B shows reactions of acetyl-CoA C-1 (Acj) with i -C-labeled and unlabeled isoptomers of oxalacetate. The abbreviations used to denote the different intermediates are O, C, K, S, and M, for oxalacetate, citrate, a-ketoglutarate, succinate and malate, respectively.

Other organic and amino acids such as citrate, isocitrate, a-ketoglutarate, succinate, glutamate, glycine, asparagine, and glutamine (see Table 3.1) are presumably synthesized through the usual intermediary metabolism reactions commonly known. 

Massey and Rogers found that minces prepared from various nematode parasites belonging to the genera Nematodirus, Ascardia, and Neo-aplectana readily oxidize pyruvate, a-ketoglutarate, succinate, fumarate, and malate. Malonate inhibits and causes an accumulation of succinate. These and various other observations support the assumption that the tricarboxylic acid cycle occurs in these organisms. 

Of special interest are the highest values, and a number of measurements giving low figures have therefore not been included. The maximum value under conditions where the substrate of respiration is more or less completely oxidized is about three. The data suggest that this also holds for the individual steps of the tricarboxylic acid cycle and its associated reactions with two exceptions. The maximum value for the reaction a-ketoglutarate — succinate appears to be four and for the step succinate —> fumarate, two. It also seems to be four for the reaction pyruvate- acetate it is to be expected to be only three for the reaction pyruvate - - oxalacetate —citrate. Slater and Holton, however, questioned the validity of the figure 4 for the reaction a-ketoglutarate succinate because they failed to find experimentally values above three. 

We detenuined the influence of oxy- and ketocarboxylic acids (succinate, fumarate, adipinate, a-ketoglutarate, isocitrate, tartrate, E-malate) on the luminescence intensity of the Eu-OxTc complex. These substances interact as polydentate ligands similarly to citrate with the formation of ternary complexes with Eu-OxTc. As to succinate, fumarate, adipinate and a-ketoglutarate this they cannot effectively coordinate with EiT+ and significant fluorescence enhancement was not observed. 

B. a-Ketoglularic acid. The ester obtained by the foregoing procedure is mixed with 600 ml. of concentrated hydrochloric acid and left overnight. The mixture is concentrated by distillation (Note 5) until the temperature of the liquid reaches 140°. It is poured into an evaporating dish and allowed to cool. The solid mass, weighing 11(3-112 g., is then pulverized. The yield of a-ketoglutaric acid is 92-93% of the theoretical for the last step, or 75-77% based upon diethyl succinate. The light tan product, obtained as described above, is suitable for most purposes, but a purer add, m.p. 109-110° (corr.) may be obtained by recrystallization from an acetone-benzene mixture. 

Bromophenol blue (3.0...4.6) aliphatic carboxylic acids [225 — 228] malonic and lactic acids [229] palmitic and lactic acids [230] malonic, glycolic, malic, citric, tartaric, ketoglutaric, galacturonic and oxalic acids [196] dicarboxylic acids, succinic acid [231] indoleacetic acid, trichloroacetic acid [232] palmitic acid, palmityl- and stearyllactic acid [223] benzoic, sorbic and salicylic acid [234] metabolites of ascorbic acid [235] chloropropionic acid [236] oligogalacturonic acids [237] amino acids, hydrocarbons, mono-, di- and triglycerides [238] xylobiose, xylose, glucose and derivatives [239] sugar alcohols [91] toxaphene [240]... 

Lsocitrate Dehydrogenase—The First Oxidadon in die Cycle m-Ketoglutarate Dehydrogenase—A Second Decarboxylation Succinyl-CoA Synthetase—A Substrate-Level Phosphoryladon Succinate Dehydrogenase—An Oxidadon Involving FAD... 

Another important piece of the puzzle came from the work of Carl Martius and Franz Knoop, who showed that citric acid could be converted to isocitrate and then to a-ketoglutarate. This finding was significant because it was already known that a-ketoglutarate could be enzymatically oxidized to succinate. At this juncture, the pathway from citrate to oxaloacetate seemed to be as shown in Figure 20.3. Whereas the pathway made sense, the catalytic effect of succinate and the other dicarboxylic acids from Szent-Gyorgyi s studies remained a puzzle. 

The catabolism of amino acids provides pyruvate, acetyl-CoA, oxaloacetate, fumarate, a-ketoglutarate, and succinate, ail of which may be oxidized by the TCA cycle. In this way, proteins may serve as excellent sources of nutrient energy, as seen in Chapter 26. 

Oxidation of 2 molecules each of isocitrate, n-ketoglutarate, and malate yields 6 NADH Oxidation of 2 molecules of succinate yields 2 [FADHg] Oxidative phosphorylation (mitochondria) 2 NADH from glycolysis yield 1.5 ATP each if NADH is oxidized by glycerol-phosphate shuttle 2.5 ATP by malate-aspartate shuttle + 3 + 5... 

Four of the B vitamins are essential in the citric acid cycle and therefore in energy-yielding metabolism (1) riboflavin, in the form of flavin adenine dinucleotide (FAD), a cofactor in the a-ketoglutarate dehydrogenase complex and in succinate dehydrogenase (2) niacin, in the form of nicotinamide adenine dinucleotide (NAD),... 

This is the decarboxylation of a (3-keto acid which undergoes smoothly even in the absence of an enzyme. Thus, it can be said that the mother nature utilizes an organic reaction with a low activation energy. The second step of the decarboxylation is the conversion of a-ketoglutaric acid to succinic acid (Fig. 3). This is the same type of reaction as the decarboxylation of pyruvic acid. 

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