Catalytic properties, enzymes

The outlook of syntheses, based on using SC-CO2 or appropriate IL/SC-CO2 biphasic system for developing integral green chemical processes due to the physical and chemical characterishcs of these neoteric solvents and the enhanced enzyme catalytic properties seems promising. 

The catalytic properties of enzymes are reflected in K, and kcat values... 

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. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

Recently, the distribution of 2,3-dihydroxybenzoate decarboxylase has been found in a variety of fungal strains (unpubhshed data), and the carboxylation activity for catechol is confirmed by the reaction using resting cells (or cell-free extract) in the presence of 3M KHCO3. The detailed comparative studies of enzyme structures and catalytic properties between 2,3-dihydroxybenzoate decarboxylase and 3,4-dihyroxybenzoate decarboxylase might explain how the decarboxylases catalyze the regioselective carboxylation of catechol. 

Copper is a component of several enzymes that have quite different catalytic properties ... 

Takenaka S, S Mnrakami, R Shinke, K Hatakeyama, H Ynknwa, K Aoki (1997) Novel genes encoding 2-aminophenol 1,6-dioxygenase from Pseudomonas species AP-3 growing on 2-aminophenol and catalytic properties of the pnrified enzyme. J Biol Chem 212 14727-14732. 

Pepsin consists of a single polypeptide chain of molecular weight 34 644 and 327 amino acid residues. Ser-68 is phosphorylated, but this phosphate may be removed without significantly altering the catalytic properties of the enzyme. As in other acid proteases, the active site is an extended area that can accommodate... 

Enzymes are protein molecules that possess exceptional catalytic properties. They are essential to plant and animal life processes. Enzymes are remarkable catalysts in at least three respects activity, specificity, and versatility. 

Sidney Altman discovered this property of RNA in the course of studies on precursor transfer RNA. It was realized that the catalytic properties of RNA are not exactly the same as those of protein enzymes, since the ribozyme is itself active and thus undergoes change during the catalytic reaction. This does not correspond to the generally accepted definition of an enzyme. Later studies, however, showed that some ribozymes are capable of acting catalytically at other RNA molecules. The ribozymes remain completely unchanged in this process, and thus fulfil the definition of a real enzyme. 

Finally, we come to enzyme models. D. W. Griffiths and M. L. Bender describe the remarkable catalytic property of certain cycloamyloses which act through formation of inclusion complexes, and in this respect recall the clefts containing the active sites in enzymes such as lysozyme and papain. 

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]. 

Tinoco, R., and VazquezDuhalt, R., Chemical Modification of Cytochrome C Improves Their Catalytic Properties in Oxidation of Polycyclic Aromatic Hydrocarbons. Enzyme and Microbial Technology, 1998. 22(1) pp. 8-12. 

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... 

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