Biochemical reactions enzyme catalyzed

Optically inactive starting materials can give optically active products only if they are treated with an optically active reagent or if the reaction is catalyzed by an optically active substance. The best examples are found in biochemical processes. Most biochemical reactions are catalyzed by enzymes. Enzymes are chiral and enantiomerically homogeneous they provide an asymmetric environment in which chemical reaction can take place. Ordinarily, enzyme-catalyzed reactions occur with such a high level of stereoselectivity that one enantiomer of a substance is formed exclusively even when the substrate is achiral. The enzyme ftimarase, for example, catalyzes hydration of the double bond of fumaric acid to malic acid in apples and other fruits. Only the S enantiomer of malic acid is formed in this reaction. 

Almost all enzymes are proteins. They provide templates whereby reactants (substrates) can bind and are favorably oriented to react and generate the products. The locations where the substrates bind are known as active sites. Because of the specific 3D structures of the active sites, the functions of enzymes are specific that is, each particular type of enzyme catalyzes specific biochemical reactions. Enzymes speed up reactions, but they are not consumed and do not become part of the products. Enzymes are grouped into six functional classes by the International Union of Biochemists (Table 2.2). 

Life depends on the existence of powerful and specific catalysts the enzymes. Almost eveiy biochemical reaction is catalyzed by an enzyme. 

These three biochemical reactions are catalyzed by hexokinase (EC 2.7.1.1), glucose-6-phosphate isomerase (EC 5.3.1.9), and 6-phosphofructokinase (EC 2.7.1.11), respectively. The EC numbers are from Enzyme Nomenclature (Webb, 1992). The first step is to write the conservation matrix for this reaction system at specified pH because that will show how to calculate the further transformed Gibbs energies of formation at specified [ATP] and [ADP]. 

In Nature, realms of complex biochemical reactions are catalyzed by enzymes, many which lack metals in their active site. Among them, nucleophilic acylation reactions are catalyzed by transketolase enzymes in the presence of coenzyme thiamine (78, vitamin Bi), a natural thia-... 

Many biochemical reactions ale catalyzed by large protein molecules called enzymes. A typical mechanism for the conversion of a biochemical substrate (S) to product (P) catalyzed by an enzyme (E) involves the following steps ... 

A first discrimination that can be made among metabolic reactions is based on the nature of the catalyst. Reactions of xenobiotic metabolism, like other biochemical reactions, are catalyzed by enzymes. However, while the vast majority of reactions of xenobiotic metabolism are indeed... 

The one-gene-one-enzyme theory generated the view that biochemical reactions are catalyzed individually by many enzymes one after another in a biochemical pathway. This view perpetuated through the development of molecular biology. 

What biochemical reaction is catalyzed by the enzyme presenilin 1 What is the role of presenilin 1 in transducing the signal induced by the binding of Delta to its receptor How are mutations in presenilin 1 thought to contribute to Alzheimer s disease ... 

The retroviral integrase (called IN) is a virus-encoded diesterase that catalyzes the incorporation (integration) of viral DNA into host DNA. Two biochemical reactions are catalyzed by this enzyme—the processing of the viral DNA ends (an endonucleolytic cleavage reaction) and then the joining of these ends to host... 

The vast majority of biochemical reactions are catalyzed by enzymes (Bagg, 2004 Copeland, 2000), which are proteins fulfilling all the three criteria of being biocatalysts efficiency (a), specificity (b) and multiple turnover (c). The term enzymes is reserved for the natural catalytic proteins in this text. Although few quasi-catalytic enzymes are known such as type I restriction endonuclease, poly(ADP-ribose) synthetase and transmethylase for 0 -methylguanine mediate specific reactions with large acceleration but are inactivated in the reaction. 

Many biochemical reactions are catalyzed by large protein molecules called enzymes. A typical mechanism for... 

The denitrification process could be described as a modular organization in which every biochemical reaction is catalyzed by specific reductase enzymes (Cuervo-Lopez et al., 2009). Four enzymatic reactions take place in the cell as follows (l) nitrate is reduced to nitrite by nitrate reductase (Nar) (ii) a subsequent reduction of nitrite to nitric oxide is carried out by nitrite reductase (Mr) (iu) afterwards, nitric oxide is reduced to nitrous oxide by the enzyme nitric oxide reductase (Nor) (iz ) finally, nitrous oxide is reduced to N2 by the enzyme nitrous oxide reductase (Nos) (Lalucat et al., 2006) (Table 9). These reactions take place when environmental conditions become anaerobic (Berks et al., 1995 Hochstein Tomlinson, 1988). The enzymatic reactions, which are thermodynamically favored, are carried out in the cell membrane and periplasmic space. Small half saturation constant values (Km) have been reported for different nitrogen substrates for some denitrifying bacteria, indicating that denitrifying enzymes have a high affinity for their substrate. However, several factors have to be considered, as the presence of small quantities of molybdenum, cooper and hem to ensure the successful enzymatic activity, as they are known cofactors for denitrifying enzymes. 

Most biochemical reactions are catalyzed by enzymes. Therefore, although quite instructive, the model for the birth-death process studied in the previous chapter is not good enough an approximation in many instances. Typically, an enzymatic process consists of a series of chemical reactions that occur at different rates, and in some occasions it is possible to identify two well-separated time scales. When this occurs, the time-scale separation can be exploited to simplify the analysis of the whole system. Below we introduce a methodology to perform such simplification. 

A great majority of the aroma compounds produced in fermented foods result from the activity of microorganisms. They derive from the conversion of food constituents via a series of biochemical reactions mainly catalyzed by microbial enzymes, although some of the enzymes either present in the raw material or added during food processing also have a role in the transformation. A few non-enzymatic reactions also occur, but they involve some coirpounds of microbial origin. 

For the bioinformatician the emphasis lies on how a gene expresses a protein -an enzyme - that catalyzes a biochemical reaction (Figure 10.3-13). 

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... 

Enzyme-Catalyzed Reactions Enzymes are highly specific catalysts for biochemical reactions, with each enzyme showing a selectivity for a single reactant, or substrate. For example, acetylcholinesterase is an enzyme that catalyzes the decomposition of the neurotransmitter acetylcholine to choline and acetic acid. Many enzyme-substrate reactions follow a simple mechanism consisting of the initial formation of an enzyme-substrate complex, ES, which subsequently decomposes to form product, releasing the enzyme to react again. 

Animal metaboHsm is based on the reactions of oxygen and organic compounds containing carbon, hydrogen, oxygen, and nitrogen and other heteroatoms. Enzymes catalyze these biochemical oxidations, which are accompHshed at about 30—40°C and frequendy proceed stepwise to produce... 

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. 

All enzymes are proteins that catalyze many biochemical reactions. They are unbranched polymers of a-amino acids of the general formula... 

Enzyme (Section 26.10) A biological catalyst. Enzymes are large proteins that catalyze specific biochemical reactions. 

---