Elucidation of Metabolic Pathways

Two sections deal briefly with procedures for investigating the pathways used in biodegradation and biotransformation. They cover briefly the application of isotopes, and of nondestructive methods that include NMR, EPR, and x-ray analysis. They should be viewed in the wider context of procedures for evaluating the effectiveness of bioremediation that are covered in Chapter 13 and their application in Chapter 14. 

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The elucidation of metabolic pathways has often been aided by the use of genetic mutations, or specific, chemical inhibitors that result in the blockage of a specific, metabolic reaction along the pathway such inhibition can sometimes lead to the accumulation of prior intermediates, and thus facilitate their isolation and identification. 

Many other microorganisms have been studied in relation to the degradation of envirtmmaiUd hydrocarbon pollutants however the identification of metabolites and elucidation of metabolic pathways has often been the prime concern of these studies, rather than the develqnnent of synthetic tnediods. Methyl-otropic bacteria are noted for their ability to degrade hydrocarbons and in some cases intermediate hy-droxylated products can be recovered. Patel and coworkers have done much of the work in this area and systems capable of converting /i-alkanes to secondary alcohols or ketones have been developed. 

Because of the very short half-life of fluorine-18 the synthetic steps for introduction of the isotope into organic substrates must be kept simple and fast. The F-labeled diagnostics are prepared immediately before use. Their main field of application is medical diagnostics and elucidation of metabolic pathways by positron emission tomography (PET) [84] (Figure 4.22). 

All these observations emphasize that tests for biodegradability carried out at high substrate concentrations may not adequately predict the rates of degradation occurring in natural ecosystems where only low concentrations of xenobiotics are encountered (Alexander 1985). This phenomenon is therefore of enormous environmental importance since it would imply the possibility of extreme persistence of low concentrations in natural ecosystems. The further exploration of this phenomenon is probably only limited in practice by the access to analytical methods for measuring sufficiently accurately substrate concentrations at the level of ng/1 or lower. Most studies that have been carried out have therefore used 14C-labeled substrates which necessarily limits the range of compounds accessible and restricts the elucidation of metabolic pathways in which only biotransformation or partial mineralization has occurred. 

The elucidation of metabolic pathways for the synthesis of compatible solutes is fundamental for the elucidation of the regulatory mechanisms during osmotic... 

The development of new PHA polymers can be achieved by genetic engineering. In addition, the elucidation of metabolic pathways could also aid in the development of new metabolic routes. 

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