Enzymes work

Most enzymes work best within a narrow pH range and are susceptible to a wide variety of compounds which inhibit or sometimes promote the activity. The majority of enzymes work most efficiently at around 40°C and at higher temperatures are rapidly destroyed. 

Bacterial a-amylases used in laundry detergents are fully compatible with detergent proteases, ie, the two enzymes work together in the wash process. During storage in both powder and Hquid detergents, the amylases are very stable in the presence of proteases. 

Enzymes work by bringing reactant molecules together, holding them, in the orientation necessary for reaction, and providing any necessary acidic or basic sites to catalyze specific steps. As an example, let s look at citrate synthase, an enzyme that catalyzes the aldol-like addition of acetyl CoA to oxaloacetate to give citrate. The reaction is the first step in the citric acid cycle, in which acetyl groups produced by degradation of food molecules are metabolized to yield C02 and H20. We ll look at the details of the citric acid cycle in Section 29.7. 

How Do Enzymes Work Citrate Synthase 1043 Focus On... The Protein Data Bank 1048... 

As enzymes work best near neutral pH, where only general acid catalysis is possible, the problem of general vs. specific acid catalysis deserves special... 

Researchers are working to understand how this enzyme works. Research on nitrogenase takes two main forms. One is an examination of the structure and operation of the enzyme to determine the details of the reactions by which N2 is converted to ammonia. The other form is the s Tithesis of artificial catalysts that mimic the operation of nitrogenase. 

Garcia-Viloca M, Gao J, Karplus M, Truhlar DG (2004) How enzymes work Analysis by modem rate theory and computer simulations. Science (Washington, DC) 303(5655) 186-195... 

The most extensive and informative enzyme work with B12 spin labels has been carried out on the enzyme ethanolamine ammonia-lyase 123). This work has employed six-coordinate 4-hydroxy-2,2,6,6-tetra-methylpiperidine-N-oxyl-5 -deoxyadenosylcobinamide. Ethanolamine ammonia lyase uses 5 -deoxyadenosylcobalamin as cofactor. Spin labeled 5 -deoxyadenosylcobinamide was used in order to determine the nature of the first step in the mechanism of action of ethanolamine ammonia lyase by determining the manner in which the Co—C bond is broken. Spin labeled 5 -deoxyadenosylcobinamide was synthesized by taking reduced diaquocobinamide and reacting it with an excess of 5 -tosyl-adenosine to give 5 -deoxyadenosylcobinamide. This was stirred for three days with a 20 fold excess of 4-hydroxy-2,2,6,6-tetramethylpiperidine... 

Garcia-Viloca, M. Gao, J. Karplus, M. Truhlar, D.G., How enzymes work analysis by modern reaction rate theory and computer simulations, Science 2004, 303, 186-195. 

Enzymes do two important things they recognize very specific substrates, and they perform specific chemical reactions on them at fantastic speeds. The way they accomplish all this can be described by a number of different models, each one of which accounts for some of the behavior that enzymes exhibit. Most enzymes make use of all these different mechanisms of specificity and/or catalysis. In the real world, some or all of these factors go into making a given enzyme work with exquisite specificity and blinding speed. 

Since catalysis is simply making a reaction go faster, it follows that the activation energy of a catalyzed (faster) reaction is lower than the activation energy of an uncatalyzed reaction. It s possible to say, then, that enzymes work by lowering the activation energy of the reaction they catalyze. This is the same as saying that enzymes work because they work. The question is how they lower the activation energy. 

This is the oldest model for how an enzyme works. It makes a nice, easy picture that describes enzyme specificity. Only if the key fits will the lock be opened. It accounts for why the enzyme only works on certain substrates, but it does not tell us why the reaction of the correct substrates happens so fast. It doesn t tell us the mechanism of the lock. A problem arises because the structure of the substrate changes as it is converted to product. So what is the enzyme complementary to—the substrate, the product, or what The answer is often the transition state (Fig. 7-2). 

Aminopeptidase N. This enzyme works in a manner similar to carboxypeptidase Y, but cleaves amino acids from the N-terminus. It can be used in the same way as carboxypeptidase Y. 

Concept "One of the great intellectual challenges presented to Science by Nature is a proper understanding of how enzymes work. At one level we can explain enzyme catalysis -what an enzyme does is bind, and thus stabilise, selectively the transition... 

Explain how enzymes work and describe the different types of enzymes. 

Only a small portion of the enzyme, called the active site, is actually involved in the catalysis reaction. In terms of the enzyme s overall shape, the active site is like a nook or a fold in its surface. The reactant molecule, called the substrate in an enzyme reaction, binds to the active site. The enzyme works by stabilizing the reaction s transition state. 

The use of enzymes to catalyze reversible reactions has proven to be an effective strategy for DCC. Enzymes work under physiological conditions (by definition), are reversible, and can also be applied to a variety of C-C and C-X bond-forming reactions. Venton and coworkers reported the first example of an enzyme-catalyzed process being used in a DCC context [32]. As their work preceded the codification of DCC in the literature, it contains little of the vocabulary that has come to define the field. It does, however, correspond perfectly with the conceptual framework of DCC, and has been widely cited as an influential early example of the DCC idea. 

DNA molecules, whether linear or circular, can be cut by means of enzymes known as restriction enzymes. A restriction enzyme is an enzyme that recognizes certain sequences of nitrogen bases and breaks the bonds at some point within that sequence. Since these enzymes work on bonds within the DNA molecule, they are sometimes called restriction endonucleases. 

Surveying our present knowledge about the enzyme activities in PVA biodegradation, a trend toward increasing integration can be seen. There are free enzymes working in the extracellular space of the cells, including also the periplasmatic volume, and there are membrane-associated enzymes that are presumably Unked to the cellular cytochrome-based electron transport chains. 

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