Enzyme catalytic properties organization

Enzymes are proteins of high molecular weight and possess exceptionally high catalytic properties. These are important to plant and animal life processes. An enzyme, E, is a protein or protein-like substance with catalytic properties. A substrate, S, is the substance that is chemically transformed at an accelerated rate because of the action of the enzyme on it. Most enzymes are normally named in terms of the reactions they catalyze. In practice, a suffice -ase is added to the substrate on which die enzyme acts. Eor example, die enzyme dial catalyzes die decomposition of urea is urease, the enzyme dial acts on uric acid is uricase, and die enzyme present in die micro-organism dial converts glucose to gluconolactone is glucose oxidase. The diree major types of enzyme reaction are ... 

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. 

Enzymes have several remarkable catalytic properties such as high catalytic power and high selectivities under mild reaction conditions, as compared with those of chemical catalysts. In the field of organic synthesis, enzymes have often been employed as catalyst functional organic compounds were synthesized by the enzymatic selective reactions [1-5]. 

The methodology of the proposed immobilization approach [164, 179] is, however, quite different from non-aqueous enzymology . Though during an immobilization procedure, enzymes have to be exposed to organic solvents, their activity is required only in aqueous solution in which resulting biosensors are operated. Hence, it is only important that the enzymes are able to retain their catalytic properties after exposure to organic solvents. 

A wide range of polymeric materials can be prepared from HIPEs. Polymerisation of the continuous phase yields highly porous cellular polymers with a monolithic structure. These are known as PolyHIPE polymers, and possess a number of unique properties including, in most cases, an interconnected cellular structure and a very low dry-bulk density. Their very high porosity favours their use as supports for catalytic species, precursors for porous carbons and inert matrices for the immobilisation of enzymes and micro-organisms. 

Ever since it was discovered that enzymes can be catalytically active in neat organic solvents, the question of how to select the correct solvent for a specified enzymatic conversion has been of crucial importance. The solvent can influence an enzymatic reaction both by direct interaction with the enzyme and by influencing the solvation of the substrates and products in the reaction medium. An example of direct interaction between solvent and enzyme is when the solvent acts as an inhibitor of the enzyme. In other cases the solvent causes conformational changes in the enzyme, thereby changing its catalytic properties. The solvent can also influence the amount of water bound to the enzyme, but this effect can largely be avoided by the use of fixed water activity as described above. Direct interaction between solvent and enzyme can influence enzyme stability as well as activity. 

The discovery in the 1980s that RNA molecules often have catalytic properties and may serve as true enzymes (ribozymes Chapter 12) stimulated new thinking about evolution. Although RNA catalysts are not as fast as the best enzymes they are able to catalyze a wide variety of different reactions. Could it be that in the early evolution of organisms RNA provided both the genetic material and catalysts The "RNA world" would have been independent of both DNA and protein.a b Later DNA could have been developed as a more stable coding molecule and proteins could have evolved as more efficient catalysts. Plausible reactions by which both cytosine and uracil could have arisen in drying ponds on early Earth have been demonstrated.6... 

Being a protein, an enzyme can lose its catalytic properties when subjected to agents such as heat, strong acids or bases, organic solvents, or other materials that denature the protein. Each enzyme catalyzes a specific reaction or a group of reactions with certain... 

The first problem faced by the enzyme industry was to prepare preparations having the same catalytic properties and yet be able to work at extremely different pH values. The pH of milk is 6.4 to 6.8 while the pH of cheese whey is closer to 4. Adjusting the pH of either feed stream is not a feasible answer to the problem. Enzyme preparations were developed from dairy yeast that are active around pH 6.7 for use in milk systems and other enzyme preparations were developed from fungal organisms active around pH 4.0 for use in cheese whey. 

Enzymes are proteins with catalytic properties. The catalytic properties are quite specific, which makes enzymes useful in analytical studies. Some enzymes consist only of protein, but most enzymes contain additional nonprotein components such as carbohydrates, lipids, metals, phosphates, or some other organic moiety. The complete enzyme is called holoenzyme the protein part, apoenzyme and the nonprotein part, cofactor. The compound that is being converted in an enzymic reaction is called substrate. In an enzyme reaction, the substrate combines with the holoenzyme and is released in a modified form, as indicated in Figure 10-1. An enzyme reaction, therefore, involves the following equations ... 

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... 

Isoenzymes are multiple forms of an enzyme that possess the ability to catalyze the enzyme s characteristic reaction but that differ in structure because they are encoded by distinct structural genes. These enzyme variants may occur within a single organ or even within a single type of cell. The forms can be distinguished on the basis of differences in various physical properties, such as electrophoretic mobility or resistance to chemical or thermal inactivation. They often have significant quantifiable differences in catalytic properties. However, all the forms of a particular enzyme retain the ability to catalyze its characteristic reaction. 

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