References, biochemical reaction Chapter

There are significant differences in the control experiments that are possible in each of these systems. Before the quantifier bio- can be applied, the possibility of abiotic alteration of the substrate during incubation must be eliminated or taken into consideration. Only the first design lends itself readily to this control. For experiments using cell suspensions, the obvious controls are incubation of the substrate in the absence of cells or using autoclaved cultures. Care should be exercised in the interpretation of the results, however, since some reactions may apparently be catalyzed by cell components in purely chemical reactions. The question may then legitimately be raised whether or not these are biochemically mediated. Two examples are given as illustration of apparently chemically mediated reactions, which have been referred to in Chapter 1 ... 

Increased conversion and product purity are not the only benefits of simultaneous separation during the reaction. The chromatographic reactor was also found to be a very suitable tool for studying kinetics and mechanisms of chemical and biochemical reactions. Some recent publications describe the results on investigation of autocatalytic reactions [135], first-order reversible reactions [136], and estimation of enantioselectivity [137,138]. It is beyond the scope of this chapter to discuss the details, but the interested reader is referred to an overview published by Jeng and Langer [139]. 

Previous chapters in this volume have been concerned with chemical reaction engineering and refer to reactions typical of those commonplace in the chemical process industries. There is another class of reactions, often not thought of as being widely employed in industrial processes, but which are finding increasing application, particularly in the production of fine chemicals. These are biochemical reactions, which are characterised by their use of enzymes or whole cells (mainly micro-organisms) to carry out specific conversions. The exploitation of such reactions by man is by no means a recent development—the fermentation of fruit juices to make alcohol and its subsequent oxidation to vinegar are both examples of biochemical reactions which have been used since antiquity. 

In this chapter we are concerned, not primarily with vitamins per se, but with coenzymes. Many coenzymes are modified forms of vitamins. The modifications take place in the organism after ingestion of the vitamins. Coenzymes act in concert with enzymes to catalyze biochemical reactions. Tightly bound coenzymes are sometimes referred to as prosthetic groups. A coenzyme usually functions as a major component of the active site on the enzyme, which means that understanding the mechanism of coenzyme action usually requires a complete understanding of the catalytic process. 

This introductory chapter describes the thermodynamics of biochemical reactions in terms of equilibrium constants and apparent equilibrium constants and avoids references to other thermodynamic properties, which are introduced later. 

Chapters 3-5 have described the calculation of various transformed thermodynamic properties of biochemical reactants and reactions from standard thermodynamic properties of species, but they have not discussed how these species properties were determined. Of course, some species properties came directly out of the National Bureau of Standard Tables (1) and CODATA Tables (2). One way to calculate standard thermodynamic properties of species not in the tables of chemical thermodynamic properties is to express the apparent equilibrium constant K in terms of the equilibrium constant K of a reference chemical reaction, that is a reference reaction written in terms of species, and binding polynomials of reactants, as described in Chapter 2. In order to do this the piiTs of the reactants in the pH range of interest must be known, and if metal ions are bound, the dissociation constants of the metal ion complexes must also be known. For the hydrolysis of adenosine triphosphate to adenosine diphosphate, the apparent equilibrium constant is given by... 

In the sense used in this chapter, generation-collection (GC) mode refers to experiments where the tip is used simply to sense redox active or electroactive species produced by the specimen under study. This usage is essentially the same as elsewhere in this volume except that the generator is a biochemical reaction or organism rather than another electrode. 

In organic, organometallic and biochemical reactions involving paired molecular (stereotopic) faces, one is confronted with two fundamental types of selectivity - facioselectivity and vectoselectivity. Facioselectivity characterizes the preferential reaction at molecular faces, and will be discussed in this chapter. Vectoselectivity refers to the relative alignment of reactants, and will be covered in the following chapter. 

It often becomes necessary in biochemical reactions to continuously add one (or more) substrate(s), a nutrient, or any regulating compound to a batch reactor, from which there is no continuous removal of product. A reactor in which this is accomplished is conventionally termed the semibatch reactor (Chapter 4) but is referred to as a fed-batch reactor in biochemical language. The fed-batch mode of operation is very useful when an optimum concentration of the substrate (or one of the substrates in a multisubstrate system) or of a particular nutrient is desirable. This can be achieved by imposing an optimal feed policy. 

In conclusion of this review of the nucleophilic properties of O2, the versatile nature of this unique anion radical should be emphasized. This chapter attempted to cover only the main features of the nucleophilic reactions of O2 with well-defined chemical substrates no attempt was made to treat any of the biochemical reactions. Moreover, in addition to nucleophilic properties, O2" is capable of reacting as a free radical as well as an electron transfer agent or electron acceptor. Thus, the understanding of this ubiquitous anion radical is probably only in its late infancy even though a computer search of the 1972-mid 1977 Chemical Abstracts revealed 850 references to super-oxide". 

While it is beyond the scope of this chapter to enter into the details concerning the physical and chemical principles involved or to consider all of the biochemical reactions which occur according to such principles, the reader may wish to consult some standard references to enhance his appreciation of this theorem (e.g., Metzler, 1977 Florkin and Stotz, 1962-1977 Mahler and Cordes, 1971). Our focus in this chapter will be to explore what constitutes a principle of intracellular metabolic control and to enumerate the various principles so far as we perceive them. 

Primary sources documented after each chapter minimize the need to search the literature, 80 illustrations provide structural information, reaction schemes, spectra, speciation diagrams, and biochemical schemes, and 22 tables present detailed information with references to primary sources. Packed with current and authoritative information, the book covers chemistry and bioinorganic vanadium chemistry in a broad and systematic manner that engenders comprehensive understanding. 

The most important biologically mediated reactions are summarized in Table 1.1 together with information about the redox environment these reactions take place in, the organisms that are usually conducting these processes, and what biochemical role these processes play for these organisms. I briefly discuss these reactions, but refer to the following chapters for details (see also Table 1.1). For a discussion of a series of additional reactions (e.g. Oxygen-Limited Autotrophic Nitrification-... 

The second metabolic pathway which we have chosen to describe is the tricarboxylic acid cycle, often referred to as the Krebs cycle. This represents the biochemical hub of intermediary metabolism, not only in the oxidative catabolism of carbohydrates, lipids, and amino acids in aerobic eukaryotes and prokaryotes, but also as a source of numerous biosynthetic precursors. Pyruvate, formed in the cytosol by glycolysis, is transported into the matrix of the mitochondria where it is converted to acetyl CoA by the multi-enzyme complex, pyruvate dehydrogenase. Acetyl CoA is also produced by the mitochondrial S-oxidation of fatty acids and by the oxidative metabolism of a number of amino acids. The first reaction of the cycle (Figure 5.12) involves the condensation of acetyl Co and oxaloacetate to form citrate (1), a Claisen ester condensation. Citrate is then converted to the more easily oxidised secondary alcohol, isocitrate (2), by the iron-sulfur centre of the enzyme aconitase (described in Chapter 13). This reaction involves successive dehydration of citrate, producing enzyme-bound cis-aconitate, followed by rehydration, to give isocitrate. In this reaction, the enzyme distinguishes between the two external carboxyl groups... 

---