Catalysts enzyme

Biological catalysts — enzymes — are usually proteins. The development of new protein syntheses is nowadays dominated by genetic protein engineering (see section 4.1.2.6). Bio-organic approaches towards novel catalytically active structures and replicating systems try to manage without biopolymers. 

Enzymes are powerful catalysts. Enzyme-catalyzed reactions are typically 10 to times faster than their uncatalyzed counterparts (Table 16.1). (There is even a report of a rate acceleration of >10 for the alkaline phosphatase-catalyzed hydrolysis of methylphosphate )... 

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

Compared to synthetic catalysts, enzymes have many advantages. First of all, being natural products, they are environmentally benign and therefore their use does not meet pubhc opposition. Enzymes act at atmospheric pressure, ambient temperature, and at pH between 4 and 9, thus avoiding extreme conditions, which might result in undesired side reactions. Enzymes are extremely selective (see below). There are also, of course, some drawbacks of biocatalysts. For example, enzymes are known in only one enantiomeric form, as they consist of natural enantiomeric (homochiral) amino acids their possible modifications are difficult to achieve (see Section 5.3.2) they are prone to deactivation owing to inappropriate operation parameters and to inhibition phenomena. 

The enzymes that catalyze the conversion of one or more compounds (substrates) into one or more different compounds (products) enhance the rates of the corresponding noncatalyzed reaction by factors of at least 10 . Like all catalysts, enzymes are neither consumed nor permanently altered as a consequence of their participation in a reaction. 

The information crisis , i.e., the fact that, because of the error frequency, longer RNA chains have so many errors after only a few reproduction steps that they can no longer be replicated, cries out for catalysts which can guarantee more exact replication. While only protein catalysts (enzymes) had been discussed until recently, ri-bozymes are now possible candidates. More complex catalysts would have required more complex matrices but where did the matrix molecules come from This serious problem, referred to by Eigen himself as an information crisis, is sometimes referred to as Eigen s dilemma (Blomberg, 1997). 

US6133016 [64] biodesulfurization catalyst. enzyme having an amino acid sequence3 set forth in SEQ ID No. 2 or an enzymatically active fragment thereof. 

The technique is versatile for determination of a wide variety of species that can participate in the CL process, such as CL substrates or CL precursors responsible for the excited state the necessary reagent for the CL reaction (usually an oxidant) some species that affect the rate or efficiency of the CL reaction activators such as catalysts (enzymes or metal ions) or inhibitors such as reductants that inhibit the CL emission fluorophores in the case of sensitized CL some species that are not directly involved in the CL reaction but that can react with other reagents in coupled reactions to generate a product that is a reactant in the CL reaction species that can be derivatized with some CL precursors or fluorophores, being determined by direct or sensitized CL. 

Reactions with soluble enzymes are generally conducted in batch reactors (Chapter 12) to avoid loss of the catalyst (enzyme), which is usually expensive. If steps are taken to prevent the loss of enzyme, or facilitate its reuse (by entrapment or immobilization onto a support), flow reactors may be used (e.g., CSTR, Chapter 14). More comprehensive treatments of biochemical reactions, from the point of view of both kinetics and reactors, may be found in books by Bailey and Ollis (1986) and by Atkinson and Mavituna (1983). 

In the context here, nutrients principally comprise compounds of nitrogen, most of which come from bacteria that employ naturally occurring catalysts (enzymes) which feed on elemental nitrogen - a process known as facing. An example is the bacterium Rhizobium which lives on beans and peas. The bacteria convert atmospheric nitrogen into ammonia, which is subsequently available for important biological molecules such as amino acids, proteins, vitamins and nucleic acids. 

Another way to solve this problem is to prevent the enzyme in the fruit from acting as a catalyst. Enzymes are sensitive to pH. Therefore, adding an acid such as lemon juice or vinegar to fruit can prevent the enzyme from acting. You may have noticed that avocado salad recipes often include lemon juice. In addition to hindering the enzyme, lemon juice contains vitamin C, which is very reactive toward oxygen. The vitamin C reacts with oxygen before the sliced fruit can do so. 

Asymmetric synthesis can refer to any process which accesses homochiral products. We will focus on asymmetric synthesis from racemic or prochiral starting materials in the presence of an enantioselective catalyst (enzyme). There are four general methodologies commonly applied kinetic resolution, dynamic kinetic resolution, deracemization and... 

Any interference with protein synthesis, through alteration of DNA function, as just mentioned, or by damage to the structures called endoplasmic reticulum, the site of such synthesis, can be devastating in many ways, because proteins are not only essential for the many structures of cells, but also because they are the body s catalysts (enzymes) for all its essential biochemical processes. 

Investigations of enzyme-catalyzed direct electron transfer introduce the basis for a future generation of electrocatalysts based on enzyme mimics. This avenue could offer new methods of synthesis for nonprecious metal electrocatalysts, based on nano-structured (for example, sol—gel-derived) molecular imprints from a biological catalyst (enzyme) with pronounced and, in some cases, unique electrocatalytic properties. Computational approaches to the study of transition state stabilization by biocatalysts has led to the concept of theozymes . " ... 

In living systems, proteins function as catalysts (enzymes), for defense (antibodies, immunoglobulins), signal transduction (hormones, receptors), metabolic regulation (hormones, enzymes, receptors, ion channels), movement (microtubules), and architecture (structural proteins such as collagen). 

Strictly speaking a catalytic cascade process is one in which all of the catalysts (enzymes or chemocatalysts) are present in the reaction mixture from the outset. A one-pot process, on the other hand, is one in which several reactions are conducted sequentially in the same reaction vessel, without the isolation of intermediates. However, not all of the reactants or catalysts are necessarily present from the outset. Hence, a cascade process is by definition a one-pot process, but the converse is not necessarily true. Clearly a cascade process is a more elegant solution, but a one-pot process that is not, according to the strict definihon, a cascade reaction may have equal practical uhlity. In this chapter we shall be primarily concerned with enzymatic cascade processes, but the occasional chemocatalytic step may be included where relevant and sometimes a sequential one-pot procedure may slip through the net. 

Like all catalysts, enzymes merely accelerate the rate but do not change the AG of a reaction or the equilibrium between reactants and products. 

For biotechnological purposes enzymes are used as biocatalysts to accelerate a desired reaction to its end point. As catalysts enzymes can catalyze a reaction in both directions. Unfortunately the name of an enzyme given by the Enzyme Commission for the classification of enzymes, and biochemistiy text books, stresses the function as a catalyst in one direction only Hydrolases, a group of enzymes of considerable importance in... 

Enzymes function as biocatalysts and, as such, are involved in all metabolic reactions. Characteristic for enzymes is their high efficiency, high specificity and extreme stereoselectivity, as well as their ability to be regulated. Analogous to chemical catalysts, enzymes do not alter the equilibrium of a reaction, but only accelerate the establishment of the equihbrium of the reaction. 

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