Transformation, biochemical

The stereochemical relationship between the reactant and the product revealed by the isotopic labeling shows that oxygen becomes bonded to carbon on the same side from which H IS lost As you will see m this and the chapters to come determining the three dimensional aspects of a chemical or biochemical transformation can be a subtle yet powerful tool for increasing our understanding of how these reactions occur... 

As the experimental tools for biochemical transformations have become more pow erful and procedures for carrying out these transformations m the laboratory more rou tine the application of biochemical processes to mainstream organic chemical tasks including the production of enantiomerically pure chiral molecules has grown... 

Enamines are used as reagents in synthetic organic chemistry and are involved in cer tain biochemical transformations... 

Before leaving this biosynthetic scheme notice that PGE2 has four chirality cen ters Even though arachidomc acid is achiral only the stereoisomer shown m the equa tion IS formed Moreover it is formed as a single enantiomer The stereochemistry is controlled by the interaction of the substrate with the enzymes that act on it Enzymes offer a chiral environment m which biochemical transformations occur and enzyme catalyzed reactions almost always lead to a single stereoisomer Many more examples will be seen m this chapter... 

Once formed cholesterol undergoes a number of biochemical transformations A very common one is acylation of its C 3 hydroxyl group by reaction with coenzyme A derivatives of fatty acids Other processes convert cholesterol to the biologically impor tant steroids described m the following sections... 

Increasingly, biochemical transformations are used to modify renewable resources into useful materials (see Microbial transformations). Fermentation (qv) to ethanol is the oldest of such conversions. Another example is the ceU-free enzyme catalyzed isomerization of glucose to fmctose for use as sweeteners (qv). The enzymatic hydrolysis of cellulose is a biochemical competitor for the acid catalyzed reaction. 

Why Do We Need to Know This Material In earlier chapters, we investigated the nature of the solid, liquid, and gaseous states of matter in this chapter, we extend the discussion to transformations between these states. The discussion introduces the concept of equilibrium between different phases of a substance, a concept that will prove to be of the greatest importance for chemical and biochemical transformations. We also take a deeper look at solutions in this chapter. We shall see how the presence of solutes is used by the body to control the flow of nutrients into and out of living cells and how the properties of solutions are used by oil companies to separate the components of petroleum. 

We were very surprised at the facility of this transformation and we had anticipated that a demonstration of its existence would be more difficult than it has been. This reaction appears to be a new type of biochemical transformation. 

Metabolites may be produced by biochemical transformation of the substrate rather than by degradation, or may result from partial abiotic reactions. These products may be (a) terminal and persistent or (b) toxic to other components of an ecosystem—including the microorganisms that produce them. Both of these represent important considerations that are illustrated by examples in this book. 

When administered as valaciclovir, aciclovir is released during absorption, and 60% of the drug reaches the bloodstream, as described above. Site activation also occurs in herpesvirus-infected cells where aciclovir is biochemically transformed to the phosphorylated active drug by virus-specific thymidine kinase [74]. 

Premuzic, E. T., and Lin Mow, S., Biochemical transformation of solid carbonaceous material. Patent No. US6294351, 2001. September 25. 

Dos Santos AB, Cervantes FJ, Van Lier JB (2004) Azo dye reduction by thermophilic anaerobic granular sludge, and the impact of the redoxmediator anthraquinone-2,6-disulfonate (AQDS) on the reductive biochemical transformation. Appl Microbiol Biotechnol 64 62-69... 

Selenium chemistry is complex, and additional research is warranted on chemical and biochemical transformations among valence states, allotropic forms, and isomers of selenium. 

Wong CS (2006) Environmental fate processes and biochemical transformations of chiral emerging organic pollutants. Anal Bioanal Chem 386 544-558... 

The detoxification and excretion of xenobiotics (i.e., foreign compounds, including diet-derived allelochemicals) involve a suite of highly complex processes that allow an organism to respond to its internal and external chemical environments. Suchmetabolic resistance involves the biochemical transformation... 

Most coenzymes have aromatic heterocycles as major constituents. While enzymes possess purely protein structures, coenzymes incorporate non-amino acid moieties, most of them aromatic nitrogen het-erocycles. Coenzymes are essential for the redox biochemical transformations, e.g., nicotinamide adenine dinucleotide (NAD, 13) and flavin adenine dinucleotide (FAD, 14) (Scheme 5). Both are hydrogen transporters through their tautomeric forms that allow hydrogen uptake at the termini of the quinon-oid chain. Thiamine pyrophosphate (15) is a coenzyme that assists the decarboxylation of pyruvic acid, a very important biologic reaction (Scheme 6). 

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. 

Despite all the problems attendant on studies of aquatic animals, however, great strides have been made in the past 10 years in defining biochemical pathways used by fishes to biotransform and eliminate xenobiotics (2, 3, 4, 5). Many of the earlier studies, especially the extensive work of DeWaide (6), defined various biochemical transformations which xenobiotics may undergo in vitro. Only in the past 10 years have in vivo studies been undertaken to define the routes and rates of elimination of xenobiotics by fishes (7, 8, 9, 10, ll). 

The abiotic characteristics of aqueous-solid phase interfaces strongly influence chemical/biochemical reactions in the interface microenvironment of aqueous-solid phases. These reactions at interfaces are controlled mainly by biotic activity. Specifically, all aqueous-solid phase microenvironments contain living microorganisms that mediate biochemical transformations. Solid phases (e.g., soil and sediment particles) usually contain billions of microorganisms, with the aqueous phase containing smaller, but still significant, populations [22,33-39]. 

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