Metabolite , generally

The duration of collection of biological samples from farm workers is determined by the excretion pattern of the active ingredient or its metabolites. Generally, collection will encompass a period of time prior to exposure to about 1-3 days beyond exposure. Background samples should be taken from workers for the 24 h prior to the first application of the test product. This will allow an up-to-date examination of the background levels of the parent or metabolites in the worker s urine. 

Flavonoids are secondary metabolites generally occurring in various plants as glycosides. The chemical structure of flavonoids shows high variety. The basic structure of flavons and flavonols is the 2-phenylbenzo-gamma-pyrone. Flavonoids generally contain two phenol rings linked with a linear three-carbon chain (chalcones) or with three carbon... 

The nonprotein amino acid /3-A -methylamino-L-alanine (BMAA) is a neurotoxin found in various species of marine cyanobacteria. This nonprotein amino acid occurs both as a free amino acid and bound to proteins.Siderophores are secondary metabolites generally produced by bacteria under iron-deficient conditions. These molecules sequester and transport ferric ion via active transport in bacteria. Some known siderophores are nonribosomal peptides that contain nonprotein amino acids with terminal amines or hydroxylamine side chains, such as exochelin Many of the known nonprotein amino... 

The analyst should also be alert to the fact that some drug residues become bound to the tissues of the animal and that this may have the effect of deactivating the toxic potential of the residue. However, determining the total concentration of the parent compound and/or its major metabolites generally ensures the greatest margin of safety. 

The identification of metabolite structures with LC/MS and LC/MS/MS techniques are an effective approach due to their ability to analyze trace mixtures from complex samples of urine, bile, and plasma. The key to structure identification approaches is based on the fact that metabolites generally retain most of the core structure of the parent drug (Perchalski et al, 1982). Therefore, the parent drug and its corresponding metabolites would be expected to undergo similar fragmentations and to produce mass spectra that indicate major substructures. 

Identiflcation/quantiflcation of a select group of metabolites, generally part of a specific pathway such as glycolysis or fatty acid synthesis. See Dunn, W.B. and Ellis, D.I., Metabolomics current analytical platforms and methodologies, Trends Anal. Chem. 24, 285-294, 2005. 

Phase-1 metabolism leads to mass shifts relative to the mass of the parent drag (Table 10.1). In principle, the type of biotransformation can be derived from this mass shift, while more information on the actual site of the modification can be derived from mass shifts of the fragment ions in the MS-MS spectrum. Identification approaches are based on the fact that metabolites generally retain a... 

The application of GC-MS in metabolomics is not trivial. Metabolites generally must be derivatized to form more volatile molecules. A critical point in this process is that these reactions represent ongoing processes and need time to reach a plateau. Hence, ample time should be allowed before subjecting tri-methylsilyl (TMS)-derivatized samples to GC-MS analysis (43). On the other hand, as indicated above, the stability of the derivatives themselves is also limited. Hence, it is not practical to prepare large numbers of samples in one step and then leave them in the autosampler for extended periods before analysis, as the potential risk for derivative decomposition to occur cannot easily be compensated for. 

Microorganisms that produce secondary metabolites generally undergo a period of logarithmic growth in which the synthesis of the secondary metabolite is negligible. When the culture enters the stationary phase, secondary metabolite production is often triggered. 

Ionized phosphate esters are ubiquitous in biochemistry principally for two reasons. First, metabolites generally must be charged, so that they will not pass through a lipid membrane and so be lost to the cell. Second, the charge must be negative, so as to repel nucleophiles and thus resist destruction by hydrolysis. Phosphates uniquely allow for these requirements. 

Polyketide biosynthesis has been well smdied and there are several reviews regarding the general construction of these metabolites. " " Generally, polyketides are initiated with acetate (or propionate) derived from either acetyl-CoA (or propionyl-CoA) or malonyl-CoA (or methyknalonyl-CoA). The chain is extended by further addition of acetate units by a ketosynthase and acyltransferase domain. The acetate units can then be altered by the inclusion of a variety of domains within the PKS pathway. Common examples of alterations are ketoreductase,... 

Auxiliary information evaluation of experience gained from other cases, literature data on plume lengths (not site-specific), sorption behavior and degradability of pollutants, possible toxic metabolites, general information on suitability of site conditions. 

The dividing line between primary and secondary metabolism is somewhat blurred in many cases. For example, amino acids are generally considered to be primary metabolites, but some are sufficiently obscure to be considered as secondary metabolites, whilst sterols which are frequently considered as secondary metabolites are essential to the cell membrane of eucaryotic species, and therefore must be regarded as primary metabolites. Generally, the primary metabolic processes are too similar from group to group to be of much use in identification, but the secondary metabolites which tend to be unique to a small group are used widely. 

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