Metabolism general considerations

General considerations. Nitroaromatic compounds, such as nitro-furans and nitrobenzenes are commercially important chemicals used as drugs, food additives or synthetic intermediates. Since there is widespread human exposure to these chemicals, their metabolism has been studied extensively. Nitroaromatic compounds are reduced by both hepatic cytosol and microsomes. The microsomal activity... 

Schoenberg R, Zink S, Staubwasser M, von Blanckenburg F (2008) The stable Crisotope inventory of solid Earth reservoirs determined by double-spike MC-ICP-MS. Chem Geol 249 294-306 Schoenheimer R, Rittenberg D (1939) Studies in protein metabolism I, General considerations in the application of isotopes to the study of protein metabolism. The normal abundance of nitrogen isotopes in amino acids, J Biol Chem 127 285-290... 

Considerable efforts have gone into the SAR studies on tetrahydrocarbazolones. F irst, substituting the indole nucleus at C6 (e.g., 151,152), a potential site of metabolism, generally reduces potency, with the exception of the 6-F derivative (150). Second, substitution at the 9-position is well tolerated (e.g., 153, 154), but some long-chain lipophilic substituents reduce activity (e.g., 155). Third, the carbonyl function in this series is critical to potent 5-HT, antagonist activity. The corresponding alcohols (156,157) and the tetrahy-drocarbozole (158) are less potent than the... 

From these general considerations we can now turn immediately to a description of some of the more important of the metabolic pathways that these methods have revealed. 

The possibUity of multiple pathways in bile acid biosynthesis in man has been discussed by Vlahcevic et al. [180-182]. A number of labelled 7 -hydroxylated intermediates in bile acid biosynthesis were administered to bile fistula patients as well as patients with an intact enterohepatic circulation. In accordance with previous work with bile fistula rats, the spedfic activity of the isolated chohc add was in general considerably lower than that of chenodeoxychohc acid. On the basis of this finding, it was suggested that a portion of chohc acid was synthesized via a route not involving initial 7a-hydroxylation of cholesterol. It must then be assumed that the administered intermediate mixes with the endogenous pool of the same steroid. However, due to compartmentation, the metabolic fate of a precursor reaching the hepatocyte might be different from that of the the same compound formed within the cell. Normally, the different precursors are present in the cells in trace amounts... 

I. General considerations concerning the natiu-aUy occurring polymer. Biopolymers 1 545-556 Anderson AJ, Dawes EA (1990) Occiurence metabolic role and industrial uses of bacterial poly-hydroxyalkanoates. Microbiol Rev 54 450-472... 

The product of the hydroxylation of tryptophan, 5-hydroxytryptophan, is rapidly decarboxylated to 5-HT by a specific decarboxylase enzyme. This is generally thought to be a soluble enzyme which suggests that 5-HT is synthesised in the cytoplasm, before it is taken up into the storage vesicles. If this is the case, then considerable losses might be incurred from its metabolism by monoamine oxidase before it reaches the storage vesicles. Indeed, this could explain why 5-HT turnover seems to greatly exceed its rate of release. 

Hybrid poplars Populus deltoides x nigra) have attracted considerable interest since they are able to transport and metabolize—even though they do not generally degrade—diverse xenobiotics ... 

Use of higher plants has attracted attention for the remediation of TCE-contaminated aquatic systems, and in particular the use of hybrid poplar (Newman et al. 1999). Although this was encouraged by the removal of labeled TCE to >90% using hybrid poplar under hydroponic conditions (Orchard et al. 2000), and the ability of hybrid poplar to metabolize TCE (Newman et al. 1997 Shang et al. 2001), there are additional considerations that must be evaluated to determine its general applicability. 

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