Acetate metabolic pathways

Compounds called carboxylic acids, which contain the -C02H grouping, occur abundantly in all living organisms and are involved in almost all metabolic pathways. Acetic acid, pyruvic acid, and citric acid are examples. 

Experimental studies of Methanosarcina and current understanding of the organism s metabolic pathway allow us to estimate the parameters in the thermodynamic term (Qusheng Jin, personal communication). The methanogens conserve about 24 kJ (mol acetate)-1, so we set AGp to 48 kJ mol-1 and m to one half. A double proton translocation occurs within the central metabolic pathway, furthermore, so, if we take these as the rate limiting steps, the average stoichiometric number / is two. 

Fig. 9. Pathway duplication the methyl citrate cycle and the glyoxylate shunt. A pathway for acetate metabolism in E. coli that uses the glyoxylate shunt is depicted on the right. Part of the methyl citrate cycle, a pathway for propionate metabolism, is depicted on the left. The pathways are analogous furthermore, three of the four steps are catalyzed by homologous enzymes. PrpE (propionyl-CoA synthase) is homologous to AcsA (acetyl-CoA synthase). PrpC (2-methyl-citrate synthase) is homologous to GltA (citrate synthase). PrpB (2-methyl-isocitrate lyase) is homologous to AceA (isocitrate lyase). The third step in the methyl citrate cycle has been suggested to be catalyzed by PrpD the second half of the reaction (the hydration) can be catalyzed by aconitase.

In summary, I have provided two examples of catabolic metabolic pathways linked to prodnction of ATP glycolysis, in which glucose is converted to lactate and pyrnvate and the citric acid cycle, in which acetate (derived from pyrnvate) is converted to carbon dioxide and water. In fact, these and other catabolic pathways generate more molecnles of ATP than 1 have so far let on. Now we need to do two things qnantitate the actnal yields of ATP and say something about how they are created. We begin by directing attention to the mitochondria. 

Citric acid cycie a central metabolic pathway responsible for converting acetate to carbon dioxide and water with the generation of chemical energy. 

The degradation of the fatty acids occurs in the mitochondrial matrix through an oxidative cycle in which C2 units are successively cleaved off as acetyl CoA activated acetic acid). Before the release of the acetyl groups, each CH2 group at C-3 of the acyl residue (the P-C atom) is oxidized to the keto group— hence the term p-oxidation for this metabolic pathway. Both spatially and functionally, it is closely linked to the tricarboxylic acid cycle (see p. 136) and to the respiratory chain (see p. 140). 

Because carbohydrates are so frequently used as substrates in kinetic studies of enzymes and metabolic pathways, we refer the reader to the following topics in Ro-byt s excellent account of chemical reactions used to modify carbohydrates formation of carbohydrate esters, pp. 77-81 sulfonic acid esters, pp. 81-83 ethers [methyl, p. 83 trityl, pp. 83-84 benzyl, pp. 84-85 trialkyl silyl, p. 85] acetals and ketals, pp. 85-92 modifications at C-1 [reduction of aldehydes and ketones, pp. 92-93 reduction of thioacetals, p. 93 oxidation, pp. 93-94 chain elongation, pp. 94-98 chain length reduction, pp. 98-99 substitution at the reducing carbon atom, pp. 99-103 formation of gycosides, pp. 103-105 formation of glycosidic linkages between monosaccharide residues, 105-108] modifications at C-2, pp. 108-113 modifications at C-3, pp. 113-120 modifications at C-4, pp. 121-124 modifications at C-5, pp. 125-128 modifications at C-6 in hexopy-ranoses, pp. 128-134. 

Betamethasone is hardly ever used orally. It has a long duration of activity and can therefore also be used for alternate-day therapy. The parenteral formulation is also the sodium phosphate salt which when given IV or IM has a rapid onset of action. There are many similarities with dexamethasone such as their metabolic pathways and the indications for which both steroids are used, like the prevention of neonatal RDS and reduction of raised intracranial pressure. Combinations of betamethasone acetate and sodium phosphate have, when used for intra-articular and intra-lesional injections, the dual advantage of a rapid onset of action together with the long duration of action of a depot preparation. 

FIGURE 4 Three types of nonlinear metabolic pathways (a) Converging, catabolic (b) diverging, anabolic and (c) cyclic, in which one of the starting materials (oxaloacetate in this case) is regenerated and reenters the pathway. Acetate, a key metabolic intermediate, is... 

Holms, W.H. (1986) The central metabolic pathways of Escherichia coli relationship between flux and control at a branch point, efficiency of conversion to biomass, and excretion of acetate. Curr. Top. Cell. Regul 28, 69-106. 

Most known thiamin diphosphate-dependent reactions (Table 14-2) can be derived from the five halfreactions, a through e, shown in Fig. 14-3. Each halfreaction is an a cleavage which leads to a thiamin- bound enamine (center, Fig. 14-3) The decarboxylation of an a-oxo acid to an aldehyde is represented by step b followed by a in reverse. The most studied enzyme catalyzing a reaction of this type is yeast pyruvate decarboxylase, an enzyme essential to alcoholic fermentation (Fig. 10-3). There are two 250-kDa isoenzyme forms, one an a4 tetramer and one with an ( P)2 quaternary structure. The isolation of ohydroxyethylthiamin diphosphate from reaction mixtures of this enzyme with pyruvate52 provided important verification of the mechanisms of Eqs. 14-14,14-15. Other decarboxylases produce aldehydes in specialized metabolic pathways indolepyruvate decarboxylase126 in the biosynthesis of the plant hormone indoIe-3-acetate and ben-zoylformate decarboxylase in the mandelate pathway of bacterial metabolism (Chapter 25).1243/127... 

Outline the metabolic pathways that are utilized by acetic acid-producing bacteria (acetogens) in the stoichiometric conversion of one molecule of glucose into three molecules of acetic acid. Indicate briefly the nature of any unusual coenzymes or metalloproteins that are required. 

The terpenoids are secondary metabolites that are found in essential oils, resins, tissues of higher plants and micro-organisms, whilst recently some have also been located in liverworts [5,6]. The terpenoids are formed from linear arrangements of isoprene units, Fig. (1), which are derived from acetate metabolism through mevalonic acid (MVA). This pathway was found to be common to the whole range of natural terpenoid derivatives... 

The biochemical isoprene units may be derived by two pathways, by way of intermediates mevalonic acid (MVA) (Figure 5.4) or 1-deoxy-D-xylulose 5-phosphate (deoxyxylulose phosphate DXP) (Figure 5.6). Mevalonic acid, itself a product of acetate metabolism, had been established as a precursor of the animal sterol cholesterol, and... 

A small part of metabolic pathways by proteinoids has been conceptualized2,5>. A flow from oxaloacetic acid to pyruvic acid 18 19) to acetic acid 20) and a side reaction from pyruvic acid to alanine, which is reversible are depicted in a conceptual integration of results2 5). 

Figure 8 Isolation of mutants deficient in the 4-OH cyclohexanecarboxylic acid metabolic pathway. Thin-layer chromatography radioautogram of ethyl acetate extractable products from doramectin fermentation dosed with [14C]-labeled cyclohexanecarboxylic acid. TLC was done on Kieselgel 60 F254 20 X 20 cm plates (E. Merck) and developed using benzene, ethyl acetate, and formic acid (25 25 2). Lanes A, uninoculated medium B and C, culture 109-123 D and E, mutant 324-52.

Fig. 5.2. Possible metabolic pathways in facultative anaerobic mitochondria. Shaded boxes show components of the electron-transport chain used during hypoxia, open boxes are components used during aerobiosis, and the hatched boxes (complex I and ATP-synthase) are components used under aerobic as well as anaerobic conditions. ASCT acetate succinate CoA-transferase, C cytochrome c, Cl, CIII and CIV complexes I, III and IV of the respiratory chain, CITR citrate, ECR enoyl-CoA reductase (such as present in Ascaris suum), ETF electron-transfer flavoprotein, ETF RQ OR electron-transfer flavoproteimrhodoquinone oxidoreductase, FRD fumarate reductase, FUM fumarate, MAE malate, OXAC oxaloacetate, PYR pyruvate, RQ rhodoquinone, SDH succinate dehydrogenase, SUCC succinate, Succ-CoA succinyl-CoA, TER trans-2-enoyl-CoA reductase (such as present in E. gracilis), UQ ubiquinone...

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