Transformation, biochemical metabolic

Two major divisions of biochemical metabolism that operate on hazardous waste species are oxic processes, which use molecular O2 as an oxygen somce, and anoxic processes, which make use of another oxidant. For example, when sulfate ion acts as an oxidant (electron receptor), the transformation sol" H2S occurs. (This has the benefit of providing sulfide, which precipitates insoluble metal sulfides in the presence of hazardous waste heavy metals.) Because molecular oxygen does not penetrate to such depths, anoxic processes predominate in the deep sediments, as shown in Figure 15.6. 

Many of the species involved in the endogenous metabolism can undergo a multitude of transformations, have many reaction channels open, and by the same token, can be produced in many reactions. In other words, biochemical pathways represent a multi-dimensional space that has to be explored with novel techniques to appreciate and elucidate the full scope of this dynamic reaction system. 

The next step in formulating a kinetic model is to express the stoichiometric and regulatory interactions in quantitative terms. The dynamics of metabolic networks are predominated by the activity of enzymes proteins that have evolved to catalyze specific biochemical transformations. The activity and specificity of all enzymes determine the specific paths in which metabolites are broken down and utilized within a cell or compartment. Note that enzymes do not affect the position of equilibrium between substrates and products, rather they operate by lowering the activation energy that would otherwise prevent the reaction to proceed at a reasonable rate. 

Indole-3-acetaldoxime (30) and 4-hydroxyphenylacetaldoxime were shown to be metabolized by plant and pest fungi to 32 and to other related indole- and 4-hydroxyphenyl carboxylic acids, however, the biochemical transformation differed between the two fungi. These biochemical transformations may be relevant to the ability of certain fungi to cause plant diseases . Compound 30 has been shown to be a key intermediate in the biosynthesis of camalexin, 3-thiazolyl-2 -yl-indole, a member of the family of phytoalexins that are produced in response to pathogen attack. It was demonstrated that CYP71A13 catalyzes the conversion of 30 to indole-3-acetonitrile, which is essential for the biosynthesis of camalexin. Thus, the literature supplies a large body of evidence for the existence of a set of enzymes dedicated to the production of the auxin, 32, from tryptophan via indole-3-acetaldoxime (30). 

Biochemical transformations of the —C=N—OH function of synthetic drugs to an NO and to nitroso intermediates " were recently demonstrated as a new pathway for metabolic activation of oxime-containing molecules. These reactions were recently explored in detail, and may underlie possible biochemical transformations of the —C=N— OH moiety in mammalian tissues, which are likely to be catalyzed by cytochrome P450 and by flavin-containing monooxygenase " . 

---