Enzyme catalytic properties protein structure

Biocatalysis refers to catalysis by enzymes. The enzyme may be introduced into the reaction in a purified isolated form or as a whole-cell micro-organism. Enzymes are highly complex proteins, typically made up of 100 to 400 amino acid units. The catalytic properties of an enzyme depend on the actual sequence of amino acids, which also determines its three-dimensional structure. In this respect the location of cysteine groups is particularly important since these form stable disulfide linkages, which hold the structure in place. This three-dimensional structure, whilst not directly involved in the catalysis, plays an important role by holding the active site or sites on the enzyme in the correct orientation to act as a catalyst. Some important aspects of enzyme catalysis, relevant to green chemistry, are summarized in Table 4.3. 

In general, biomolecules such as proteins and enzymes display sophisticated recognition abilities but their commercial viability is often hampered by their fragile structure and lack of long term stability under processing conditions [69]. These problems can be partially overcome by immobilization of the biomolecules on various supports, which provide enhanced stability, repetitive and continuous use, potential modulation of catalytic properties, and prevention of microbial contaminations. Sol-gel and synthetic polymer-based routes for biomolecule encapsulation have been studied extensively and are now well established [70-72]. Current research is also concerned with improving the stability of the immobilized biomolecules, notably enzymes, to increase the scope for exploitation in various... 

Both enzymes and antibodies are proteins. Antibodies consist of subunits with multiple domains, just as do some enzymes. Both enzymes and antibodies have binding sites for small molecules between domains or subunits. In view of such similarities it isn t surprising that some antibodies have catalytic properties. The possibility was suggested in 1969 by Jencks 3 He also proposed that injection of a mouse with a hapten, that resembled a transition state for an enzyme, might induce formation of antibodies complementary to the transition-state structure. These might be catalytic. By the early 1980s such antibodies were discovered.1 d Some of the first catalytic antibodies (also dubbed abzymes) had esterase activity. The haptens used to induce antibody formation were phosphonates such as the following.e f... 

In the mimicking of an enzymatic process there is no need to copy the structure of protein and coenzyme groups and all stages of this process. In the course of evolution, Nature created enzymes in specific conditions in certain media and utilized certain building materials . Besides chemical functions, enzymes bear many other obligations, serving as units of complicated enzymatic and membrane ensembles. These conditions have not always been the most favorable for catalytic properties and the stability of enzymes. 

Reversible covalent modification. The catalytic properties of many enzymes are markedly altered by the covalent attachment of a modifying group, most commonly a phosphoryl group. ATP serves as the phosphoryl donor in these reactions, which are catalyzed by protein kinases. The removal of phosphoryl groups by hydrolysis is catalyzed by protein phosphatases. This chapter considers the structure, specificity, and control of protein kinase A (PKA), a ubiquitous eukaryotic enzyme that regulates diverse target proteins. 

It is now well established that the catalytic properties of a wide variety of enzymes remain intact in organic solvents (11-13). These findings imply that proteins may also retain their native struetures when lyophilized and dispersed in organic solvents. Evidence has been obtained that crystallized proteins have essentially the same structure in water and organic solvent (14,15). In the lyophilized state, proteins are also in a nonaqueous environment and it is expected their physico-chemical properties will differ from that in solution, as the dynamic conformational equilibria that exits in solution will be absent. Some physico-chemical studies indicate that the structure of the lyophilized state is very similar to that in solution (16-18), while others indicate that there is some limited but reversible conformational change (19-24). There are likely to be... 

Proteins that have catalytic properties are called enzymes (i.e.. enzymes are biological catalysts of protein nature). Some enzymes have full catalytic reactivity per sc these are considered to be simple proteins because they do not hiive a nonprotein moiety. Other enzymes are conjugated proteins, and the nonprotcin structural components arc necc.ssary for reactivity. Occasionally, enzymes require metallic ions. Because enzymes are proteins or conjugated proteins, the general review of protein structural studies presented above in this chapter (e.g.. protein conformation and denaturation) is fundamental to the following topics. Conditions that affect denaturation of proteins usually have an adverse effect on the activity of the enzyme. 

The hrst zinc enzyme to be discovered was carbonic anhydrase in 1940, followed by carboxypeptidase A some 14 years later. They both represent the archetype of mono-zinc enzymes, with a central catalytically active Zn " " atom bound to three protein ligands, and the fourth site occupied by a water molecule. Yet, despite the overall similarity of catalytic zinc sites with regard to their common tetrahedral [(XYZ)Zn " "-OH2] structure, these mononuclear zinc enzymes catalyse a wide variety of reactions, as pointed out above. The mechanism of action of the majority of zinc enzymes centres around the zinc-bound water molecule, which is best represented as Zn -OH2. What determines the catalytic properties of each enzyme is not only the nature of the donor ligands, but also the distance that separates them in the amino acid sequence of the protein, lypically (Table 12.1), two of the ligands are separated by only 1—3 amino acids, whereas the third ligand is separated by a longer spacer of between 5 and 196 residues. 

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