Enzymes worked examples

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. 

WORKING EXAMPLES OF ENZYMES AS FUEL CELL CATALYSTS POSSIBILITIES FOR NOVEL DESIGNS AND APPLICATIONS... 

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. 

TThe growth of cancer cells is not controlled in the same way as cell growth in most normal tissues. Cancer cells have greater requirements for nucleotides as precursors of DNA and RNA, and consequently are generally more sensitive than normal cells to inhibitors of nucleotide biosynthesis. A growing array of important chemotherapeutic agents—for cancer and other diseases—act by inhibiting one or more enzymes in these pathways. We describe here several well-studied examples that illustrate productive approaches to treatment and help us understand how these enzymes work. 

Finally, although the All desaturase from cabbage looper is probably the most studied enzyme involved in these pathways, much more work should be done with it and related enzymes. For example, it only produces Z products and does not function efficiently with 14 carbon substrates, indicating a fundamental difference with the enzyme from redbanded leafroller moths, which desaturates 14-carbon acids to give a mixture of Z and E product (22). Projects such as this may well prove technically difficult, but will provide great insight into the enzymatic mechanisms. 

In compartmentation systems (or precursor activation systems), precursors and activating enzymes work synergistically to exert plant defense however, other kinds of synergism were observed. For example, chemicals that enhance the toxicity of furanocoumarin by inhibiting detoxifying enzyme of insects (i.e., cytochrome P-450 monooxygenase) coexist with furanocoumarin in plants.5... 

Another of such long-term interests is the study of the dynamic aspects of the protein molecules, the amplitude of internal motions and the asymmetry of the motion. The dynamic properties of residues near the active site of an enzyme, for example, are absolutely critical for it to carry out its function. NMR is in a unique position to study these problems at an exquisite level of detail. So far, we have not really reached this ultimate goal yet, but we re working on new techniques that will hopefully provide us detailed insight into what exactly is going on within the protein during a reaction. 

Four examples of structurally characterised, vanadate-inhibited phosphorylation enzymes working on the hydrolysis of phospho-ester bonds in nucleotides I, the vanadate-uridine complex of bovine pancreatic ribonuclease-A II, the vanadate complex of ribonuclease-Tj from the fungus Aspergillus oryzae-. III, the vanadate-uridine complex of cyclic nucleotide phosphodiesterase from the cruciferous plant Arabidopsis thaliana-, IV, human tyrosyl-DNA phosphodiesterase (Ur = uridine). 

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