Succinate metabolism

In this case, succinate metabolism to oxaloacetate produces 5 ATPs from the oxidation of the NADH and FADH2—2 from die FADH2 and 3 from the NADH. Two O s are consumed, 1 for each of the NADH and FADH2 molecules. The P/O is then 5/2 = 2.5. Thus the P/O can be a nonintegral number. 

Drug interactions are possible if CYP450 inhibitors are given with solifenacin succinate (metabolized by 3A4 isoenzyme) or darifenacin (metabolized by 2D6 and 3A4 isoenzymes). 

One of these alternate models, postulated by Gunter Wachtershanser, involves an archaic version of the TCA cycle running in the reverse (reductive) direction. Reversal of the TCA cycle results in assimilation of CO9 and fixation of carbon as shown. For each turn of the reversed cycle, two carbons are fixed in the formation of isocitrate and two more are fixed in the reductive transformation of acetyl-CoA to oxaloacetate. Thus, for every succinate that enters the reversed cycle, two succinates are returned, making the cycle highly antocatalytic. Because TCA cycle intermediates are involved in many biosynthetic pathways (see Section 20.13), a reversed TCA cycle would be a bountiful and broad source of metabolic substrates. 

Wachtershanser has also suggested that early metabolic processes first occurred on the surface of pyrite and other related mineral materials. The iron-sulfur chemistry that prevailed on these mineral surfaces may have influenced the evolution of the iron-sulfur proteins that control and catalyze many reactions in modern pathways (including the succinate dehydrogenase and aconitase reactions of the TCA cycle). 

Succinic add source of carbon and energy improves metabolic balance between carbon flux from glucose and oxidation throgh TCA cyde. 

Succinic semialdehyde (SSA) is synthesized in the mitochondria through transamination of y-aminobutyric acid (GABA) by GABA transaminase (GABA-T). Most of the SSA is oxidized by SSA dehydrogenase (SSA-DH) to form succinate, which is used for energy metabolism and results in the end products CO2 + H2O, which are expired. A small portion of SSA (<2%) is converted by SSA reductase (SSA-R) in the cytosol to GHB. GHB may also be oxidized back to SSA by GHB dehydrogenase (GHB-DH). 

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),... 

It has been shown that pure cultures of bacteria under anaerobic denitrifying conditions may produce benzylsuccinate as a metabolite of toluene (Evans et al. 1992 Migaud et al. 1996 Beller et al. 1996). Demonstration of this and the corresponding methylbenzyl succinates from xylenes has been used to demonstrate metabolism of toluene and xylene in an anaerobic aquifer (Beller et al. 1995, 2002). 

Both the synthesis of propionate and its metabolism may take place under anaerobic conditions. In Desulfobulbuspropionicum, degradation could plausibly take place by reversal of the steps used for its synthesis from acetate (Stams et al. 1984)—carboxylation of propionate to methylmalonate followed by coenzyme Bi2-mediated rearrangement to succinate, which then enters the tricarboxylic acid cycle. The converse decarboxylation of succinate to propionate has been observed in Propionigenium modestum (Schink and Pfennig 1982),... 

Bartholomew BA, MJ Smith, PW Trudgill, DJ Hopper (1996) Atropine metabolism by Pseudomonas sp strain AT3 evidence for nortropine as an intermediate in atropine breakdown and reactions leading to succinate. Appl Environ Microbiol 62 3245-3250. 

Rabus R, H Wilkes, A Behrends, A Armstroff, T Fischer, AJ Pierik, F Widdel (2001) Anaerobic initial reaction of -alkanes in a denitrifying bacterium evidence for (1-methylpentyl) succinate as initial product and for involvement of an organic radical in -hexane metabolism. J Bacteriol 183 1707-1715. 

Aliphatic compounds Several water-soluble simple organic acids and alcohols are cannon plant and soil constituents. They include methanol, ethanol, n-propanol and butanol (40), and crotonic, oxalic, formic, butyric, lactic, acetic and succinic acids (41, 42), all of which inhibit seed germination or plant growth. Under aerobic conditions, however, aliphalic acids are metabolized in the soil and therefore, should not be considered a major source of allelopathic activity (40). 

Tielens, A.G. and Roos, M.H. (1994) Differential expression of two succinate dehydrogenase subunit-(3 genes and a transition in energy metabolism during the development of the parasitic nematode Haemonchus contortus. Molecular and Biochemical Parasitology 66, 273-281. 

In the presence of the inhibitor rotenone (to prevent the oxidation of NADH by the electron transport chain), succinate can be metabolized only to fumarate, producing an FADH2 in the process. 

In the absence of rotenone, the NADH that is made from the conversion of succinate to oxaloacetate can be oxidized by the electron transport chain. The metabolism of succinate then becomes... 

GABA is metabolized by GABA-T to form succinic semialdehyde. To conserve the available supply of GABA,... 

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