Metabolic pathways tracing

Radioisotopes are used as long-lasting power sources, to study the environment, and to track movement. They are used in biology to trace metabolic pathways, in chemistry to trace reaction mechanisms, and in geology to determine the ages of rocks. 

Tracing labeled carbon atoms through metabolic pathways would, at first glance,1 appear to be a pretty irrelevant thing to make you do. But if you ve got to do it, there are a couple of conceptual tricks that make it somewhat easier. 

Other nuclei, such as 13C or 31P, may be used to study other metabolite pools, or they can complement H-NMR to create more sophisticated NMR spectra. 13C-NMR provides a greater spectral range ( 200 ppm) than H-NMR ( 15 ppm). Although lower natural abundance of 13C (1.1%) yields lower sensitivity, it also provides an opportunity to use isotopic enrichment to trace specific metabolic pathways with enhanced sensitivity.4 31P can observe high-energy phosphate metabolites such as adenosine triphosphate. 

Juwadi PR et ai, Genomics reveals traces of fungal phenylpropanoid-flavonoid metabolic pathway in the filamentous fungus Aspergillus oryzae, J Microbiol 43 475-486, 2005. 

Laying hens eliminate sulfamethazine rapidly by metabolic pathways that include both hydroxylation and acetylation (205). Within 3 days of the last sulfamethazine administration, plasma concentrations of the drug and its metabolites fell below the level of 0.02 ppm. In eggs, increase of sulfamethazine in egg white and yolk occurs during the whole medication period. Residues of the parent drug could be detected in the eggs laid 7 days after the cessation of the administration (210). Traces of N -acetylsulfamethazine and hydroxyl metabolites were also detectable up to day 3 after drug withdrawal. 

A self-replicating polymer would quickly use up available supplies of precursors provided by the relatively slow processes of prebiotic chemistry. Thus, from an early stage in evolution, metabolic pathways would be required to generate precursors efficiently, with the synthesis of precursors presumably catalyzed by ri-bozymes. The extant ribozymes found in nature have a limited repertoire of catalytic functions, and of the ribozymes that may once have existed, no trace is left. To explore the RNA world hypothesis more deeply, we need to know whether RNA has the potential to catalyze the many different reactions needed in a primitive system of metabolic pathways. 

The study of sulfide metabolism at hydrothermal vents dictated the development of methods that could process hundreds of samples which contain complex mixtures of sulfur compounds in a variety of blood, seawater and tissues samples. In addition, we needed the capability of using "S-radiolabeled compounds for the tracing of complex sulfur metabolic pathways in bacteria and animal compartments of the different hydrothermal vent symbioses. In some instances, in situ sampling by submersibles at depths of 2500 meters with associated recovery times of two hours necessitated the remote derivatization of samples at depth prior to recovery. None of the above methods completely met our needs. We have adapted the bimane-HPLC method (24.351 for shipboard use and have found it a particularly robust method for studying a number of questions concerning the role of reduced sulfur compounds in the marine environment. 

Although the rapid advances of the medical sciences in recent decades are the result of many causes, one of the most important has been the discovery and use of radiotracers, which are radioactive nuclides that can be introduced into organisms through food or drugs and whose pathways can be traced by monitoring their radioactivity (see Fig. 21.8). For example, the incorporation of nuclides such as C and 2 P into nutrients has produced important information about metabolic pathways. 

Metabolic disorders are diseases caused by errors in metabolism. The term metabolism refers to the sum of the chemical reactions in the body. Metabolic problems can be traced to numerous metabolic pathways found in cells throughout the body. 

Without knowing the detailed metabolic pathways, many fermentative products today are obtained via aerobic fermentation processes. Probably the largest scale, single product aerobic fermentations are those used to produce single cell protein (SCP), or yeast biomass from hydrocarbons [63]. Here, an aerated yeast suspension in water, which contains trace nutrients is used to generate yeast biomass from gas oil, a mixture of straight chain hydrocarbons in the Cn to C20 range (Eq. 16.23). 

I. 0). The isotopic composition of alkanes and of other classes of compounds can also be used as a general source input indicator. Isotopic fractionation resulting from the metabolic pathways involved in the synthesis of biologically produced compounds, when preserved in a dlagenetlc product, is frequently used to differentiate between terrestrial and aquatic sources. Hydrogen and carbon isotopic compositions of biogenic methanes from shallow aquatic environments is discussed in a later chapter of this volume (R. A. Burke and W. M. Sackett). The applicability of carbon isotopic data to tracing the source of deep-sea Mesozoic sediments is discussed by R.M. Joyce and E. S. Van Vleet. 

Other F-labeled tracers, for example different fluorinated dopamine derivatives, enable, e.g., very differentiated diagnosis of Parkinson s disease [86]. Fluorine-18-derivatized diagnostics have also been used to trace the metabolic pathway of drugs through the body in clinical tests. The radiation dose to which the test person is subjected is in the same range as, e. g., that used for a stomach X-ray examination. Examples of F-labeled radiopharmaceuticals and their target sites and applications are illustrated in Scheme 4.39. 

A substantial number of pharmaceutically and clinically related problems require the detection and determination of small amounts of metal ions and other inorganic constituents of biological and xenobiotic substances (1-3). Some obvious examples are the detections of heavy metals and lithium in biological fluids and tissue samples in cases of suspected intoxication and the determination of potassium for purposes of quality control in intravenous solutions to be given to cardiac patients. Trace amounts of nonmetals such as selenium and iodine, which are associated with the functions of coenzymes or hormones, also must be analyzed in order to determine their roles in metabolic pathways. 

Kinase domain mutations are not the only mechanism that may lead to drug resistance. As noted in Section 5.2, several additional mechanisms have been identified by which cells can escape or mitigate the effect of dosing with imatinib. In several other cells, resistance has been traced to one or several factors associated with changes in signaling or metabolic pathways. Several examples are highlighted in this section, in which resistance has been traced to one or several factors that do not involve kinase domain mutations. 

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