Metabohc conversions

Concurrent administration of aspirin reduces ketoprofen protein binding and increases its clearance. Salicylate also reduces the metabohc conversion of ketoprofen to its conjugates and their renal elimination, and enhances its conversion to non-conjugated metabohtes (15). 

Metabohc conversion of aflatoxin Bj to the putative reactive electrophihc aflatoxin Bi-2,3-epoxide by a cytochrome P45o-hnked monooxygenase system is a prerequisite for exerting its carcinogenic and mutagenic potential (Swenson et al. 1977, Fahmy et al. 1978). 

The important metabohc conversions of drugs fall into four reaction classes oxidations, reductions, hydrolyses, and syntheses or conjugations. Gillette [21] has presented a very thorough discussion of the individual mechanisms and their apphcation to various classes of drugs. It is interesting to note that only eleven different methods are known by which vertebrates destroy foreign substances. Sufficient data has not been accumulated for invertebrates, but a similar situation seems to exist there also. 

Only small amounts of free T are present in plasma. Most T is bound to the specific carrier, ie, thyroxine-binding protein. T, which is very loosely bound to protein, passes rapidly from blood to cells, and accounts for 30—40% of total thyroid hormone activity (121). Most of the T may be produced by conversion of T at the site of action of the hormone by the selenoenzyme deiodinase (114). That is, T may be a prehormone requiring conversion to T to exert its metaboHc effect (123). 

Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

In mminants, whose main metabohc fuel is short-chain fatty acids formed by bacterial fermentation, the conversion of propionate, the major glucogenic product of rumen fermentation, to succinyl-CoA via the methyhnalonyl-CoA pathway (Figure 19—2) is especially important. 

In practice, the primary objective of chemical thermodynamics is to estabhsh a criterion for determining the feasibility or spontaneity of a given physical or chemical transformation. For example, we may be interested in a criterion for determining the feasibility of a spontaneous transformation from one phase to another, such as the conversion of graphite to diamond, or the spontaneous direction of a metabohc reaction that occurs in a cell. On the basis of the first and second laws of thermod5m-amics, which are expressed in terms of Gibbs s functions, several additional theoretical concepts and mathematical functions have been developed that provide a powerful approach to the solution of these questions. 

Metabohc derivatives of the fat-soluble vitamin retinol, which was first described in 1913. These metabolites play a central role in the visual process where the primary photoevent is attended by conversion of ll-cA-retinal to all-rrans-retinal. The oxidized metabolite retinoic acid is an agonist in cell growth and proliferation. 

The reaction that gives chemical energy to heat engines in cars (hydrocarbon oxidation) has to obey the Carnot cycle efficiency limitation (1 - T r,jg,). With low around body temperature (37 °Q, the metabohc would have to be 337 °C to explain this metabolic efficiency in terms of a heat engine. Thus, the body energy conversion mechanism cannot use this means to get the energy by which it works. 

Anandamide may escape metabohc degradation by FAAH through its enzymatic oxygenation. It was shown that anandamide may be metabohzed by lipoxygenases (Ueda et al., 1995 Hampson et al., 1995 Edgemond et al., 1998), COX-2 (Yu et al., 1997), or P450 hydroxylates (Bomheim et al., 1993,1995). The functional significance of such metabolic conversion is yet to be identified. 

The derivatization that most effectively lowered the metabohc rate was the demethylation of the 3-methoxy group (Table 6). The conversion of the 3-methoxy... 

The rate of 22 6n-3 synthesis from 18 3n-3 in ZS patient cell lines was 5% of that in control cells, whereas the r iolabeled intermediates of 22 6n-3 synthesis showed no significant difference between the two cell lines. This result supports the proposal that synthesis of 22 6n-3 proceeds via the revised n-3 frtty acid metabolic pathway shown in Figure 1. In this pathway, 18 3n-3 is converted to 24 6n-3, which is transported to peroxisomes for conversion to 22 6n-3 via P-oxidation. We also studied 22 6n-3 synthesis in vivo in PEX2 knockout mice, an animal model for human ZS (19,20), and in control litter-mates after an intraperitoneal injection of [l- C]18 3n-3. Measurement of 22 6n-3 synthesis rates and quantitation of metaboHc intermediates indicated that the revised pathway is operational in vivo and that functional peroxisomes are essential for this process (Su et al., unpublished observation). 

Justin GA, Zhang Y, Cui XT, Bradberry CW, Sun M, Sclabassi RJ. A metabolic biofuel cell conversion of human leukocyte metabohc activity to electrical currents. J Biol Eng 2011 5 5. 

FAs from the breakdown of TAG cannot be used for gluconeogenesis, rather they are oxidized in tissues to produce acetyl CoA. Acetyl CoA inhibits the conversion of pyruvate (from glycolysis) to acetyl CoA. Therefore glucose is spared, and FAs are used as a metaboHc fuel instead. The surplus acetyl CoA may exceed the capacity of the TCA cycle, and therefore is converted to KBs. KBs are metaboHzed by most tissues except erythrocytes, which can only use glucose. 

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