Glyoxalate cycle

Pyrindicin.—The pattern of C n.m.r. signal enhancement observed on incorporation of [1- C]- and [2- C]-acetate and [l- C]propionate into pyrindicin (9) in Streptomyces griseoflavus var. pyrindicus indicates that the metabolite is formed from five acetate units and one propionate unit, as shown in (9). Some labelling by acetate of the propionate unit was observed, which was interpreted as being the result of metabolism via both the tricarboxylic acid and glyoxalate cycles. 

Secondary carbon-sources, i.e., intermediates of citrate or glyoxalate cycle are essential for good saccharide utilisation by saprophytically cultivated Claviceps strains. 

An influence of carbon sources on the growth of P. sizovae and biosynthesis of agroclavine-I and epoxyagroclavine-I, as well as the activity of key enzymes of the Krebs cycle, the pentose phosphate pathway and glyoxalate cycle were studied (Kozlovsky and Vepritskaya, 1987). The best alkaloid productivity was observed with mannitol and fumaric acid as the carbon sources. A combination of sorbitol with fumaric acid stimulated epoxyagroclavine-I synthesis. A high alkaloid production was accompanied by high activity of the pentose phosphate cycle and low activity of the Krebs cycle. 

Plants, hut not animals, are able to synthesize glucose from acetyl CoA by a pathway that begins with the glyoxalate cycle. One of the steps in the cycle is the conversion of isocitrate to glyoxalate plus succinate, a process catalyzed by isocitrate lyase. Propose a mechanism for the reaction. 

Macrocycles have been prepared by formation of macrocyclic imines as well as by using variations of the Williamson ether synthesis ". Typically, a diamine or dialdehyde is treated with its counterpart to yield the Schiff s base. The saturated macrocycle may then be obtained by simple reduction, using sodium borohydride, for example. The cyclization may be metal-ion templated. In the special case of the all-nitrogen macrd-cycle, 15, the condensation of diamine with glyoxal shown in Eq. (4.14), was unsuccess-ful ... 

Figure 3.38 a The general enamine catalytic cycle in the presence of L-proline b an example of an asymmetric Mannich-type addition of cyclohexanone to iminoethyl glyoxalate, catalyzed by a proline tetrazole derivative. 

It is unknown when and how cooperation with amino acids, peptides, and proteins started to evolve into an RNA-protein world. However, there is an upper size limit of RNAs, which is due to a threshold error of RNA replication. The heart of the core necessary to launch the process of chemical evolution towards the RNA world must have consisted of a number of pathways for the synthesis of organic molecules from CO2, N2, and H2. Additional pathways for the synthesis of amino acids, ribose, purines, pyrimidines, coenzymes, and lipids likely combined into this core. Overall, the number of pathways required to generate nucleotides is relatively small. Pyruvate, ammonia, carbon dioxide, ATP, and glyoxalate suffice to synthesize virtually the compounds required for metabolic cycles. It seems likely that once the RNA world existed that thereafter an RNA-Peptide world developed. Details are on the following website http //www.sciencedirect.com - Cell, Volumel36, Issue 4, page 599, and a description follow below. 

Knowles and co-workers observed (V/K) at C-1 of glyoxalate by analyzing the isotopic composition of the malate produced in the reaction at early and late stages (23). In order to measure this ratio accurately they developed a procedure to convert C-2 of malate to carbon dioxide. Through a series of enzymic reactions, C-2 was converted to the carbonyl carbon of the acetyl group of acetyl-carnitine (through the reaction sequence malate — pyruvate — acetyl-CoA - acetylcarnitine). The labeled carbon then was carried flirough another cycle back to malate, but in this case the label was in the carboxylate carbon at C-4 (acetyl-carnitine acetyl-CoA 4-[ 3C]malate). Malic enzyme converts this to pyruvate and labeled carbon dioxide, whose isotopic ratio is determined by mass spectrometry. 

Milton et al. have demonstrated the preparation of substrates for the Pummerer reaction by the addition of thiols to glyoxalates. Procter et al have extended this methodology to include fluorous phase tag thiols which then led to Pummerer intramolecular cyclative capture under the appropriate reaction conditions. The methodology efficiently resulted in tagged heterocyclic frameworks which could be further modified in a number of... 

Although the positive evidence in support of the tricarboxylic acid cycle is thus incomplete in the case of some animal tissues, it may be said that the data on the whole favor the view that the cycle is operative in animal tissues generally. Such data as are available—on the occurrence of the enzymes and the effect of malonate—are in accordance with this view, and no positive evidence in support of major alternative pathways of the oxidation of acetate has so far come to light. A direct oxidation of acetate via glycollate, glyoxalate, and oxalate is, according to isotope experiments of Weinhouse and Friedmann, of no quantitative importance in the rat. 

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