Metabolism processes concepts

The term intermediary metabolism is used to emphasize the fact that metabolic processes occur via a series of individual chemical reactions. Such chemical reactions are usually under the control of enzymes which act upon a substrate molecule (or molecules) and produce a product molecule (or molecules) as shown in Figure 1.1. The substrates and products are referred to collectively as intermediates or metabolites . The product of one reaction becomes the substrate for another reaction and so the concept of a metabolic pathway is created. 

Sometimes, ADME considerations can be used to the advantage of the drug designer. This is particularly true when applied to the concept of a prodrug. A prodrag is a drug molecule that is biologically inactive until it is activated by a metabolic process. The active compound is released as a metabolite. 

As mentioned previously, toxicity is a relative event that depends not only on the toxic properties of the chemical and the dose administered but also on individual and interspecific variation in the metabolic processing of the chemical. The first recognition of the relationship between the dose of a compound and the response elicited has been attributed to Paracelsus (see Section 1.1.3). It is noteworthy that his statement includes not only that all substances can be toxic at some dose but that the right dose differentiates a poison from a remedy, a concept that is the basis for pharmaceutical therapy. 

Concepts of metabolic processes may be distorted if they are based solely on energy. We have already shown that protein production and the accumulation of lipids differ between the three races of European anchovy, but the energy equivalents of the body weights alter identically in all three (Shulman and Urdenko, 1989), even though the metabolic patterns differ. No fish farmer will consider only the caloric content of the feed, but will concentrate on a proper balance of constituents. Only considerations of both matter and energy will give a true understanding of all the processes involved. 

Several proof-of-concept studies have demonstrated how various metabolic processes can be utilized for contrast formation in SECM imaging. From a methodological point of view, two possibilities exist. The scanning... 

Lindon J C, Nicholson J K, Holmes E, et al. (2000). Metabonomics Metabolic processes studied by NMR spectroscopy of biofluids. Concepts Magn. Reson. 12 289-320. 

A global overview of bioenergetics can be obtained by using thermodynamic ideas in the study of networks of reactions. The detailed chemistry of metabolic processes is discussed later (Chaps. 10 to 14). The key concepts are as follows. 

The concept has often been taught that the drug metabolism process is one of making compounds more polar to facilitate excretion. This view has some general validity but many exceptions exist. 

Since Cotzias s 1958 review [1], a number of excellent monographs, chapters, and review articles have appeared [2-23]. The period prior to 1984 is perhaps best summarized by the multi-author monograph [18], with regard to concepts of nutrition and transport, interaction with several important enzymes and metabolic processes, and as a biophysical probe. The references in the current review result from a selective search of the... 

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