Proteins catalysts for

Self-splicing KNA. The precursor to the 26S rRNA of Tetrahymena contains a 413-nucleotide intron, which was shown by Cedi and coworkers to be selfsplicing, i.e., not to require a protein catalyst for maturation.581 582 This pre-rRNA is a ribozyme with true catalytic properties (Chapter 12). It folds into a complex three-dimensional structure which provides a binding site for free guanosine whose 3-OH attacks the phosphorus at the 5 end of the intron as shown in Fig. 28-18A, step a. The reaction is a simple displacement on phosphorus, a transesterification similar to that in the first step of pancreatic ribonuclease action (Eq. 12-25). The resulting free 3-OH then attacks the phosphorus atom at the other end of the intron (step b) to accomplish the splicing and to release the intron as a linear polynucleotide. The excised intron undergoes... 

The effect of irreversible inhibition of acetylcholinesterase has been used in dendrimer-based electrochemical biosensors for environmental applications. Acetylcholinesterase is a very efficient protein catalyst for the hydrolysis of its physiological substrate acetylcholine. Organophosphorus and carbamic pesticides, heavy metals and detergents exert strong specific... 

Fiedorowicz, M., Konieczna-Molenda, A., Khachatryan, G. Tomasik, P. (2006). A metod of stimulation of protein catalysts for biochemical reactions, particularly enzymem for preparation of saccharides. Polish Patent, Appl. P-379950. 

Certain derivs. of importance in peptide synth. have been listed separately under the name of the A-protecting group. Occurs widely in peptides and proteins. Catalyst for Knoevenagel condensations. Used for detn. of Cu, Au. Cryst. (EtOH aq.). Sol. H2O si. sol. EtOH. Mp 262° dec. 2.35 p. 2 9.78 (25°). Isoelectric point 5.97. Sweet taste. 

An enzyme is a special protein that acts as a catalyst for biochemical reactions. 

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

Tnflic acid is a useful reagent for the removal of protecting groups (deblocking) in synthetic proteins [67] At the same time, it is an excellent catalyst for the protection of a variety of phenols in the form of their terf-butyl ethers [5(5] (equation 37)... 

An enzyme—usually a large protein—is a substance that acts as a catalyst for a biological reaction. Like all catalysts, an enzyme doesn t affect the equilibrium constant of a reaction and can t bring about a chemical change that is otherwise unfavorable. An enzyme acts only to lower the activation energy for a reaction,... 

Microelectronic circuits for communications. Controlled permeability films for drug delivery systems. Protein-specific sensors for the monitoring of biochemical processes. Catalysts for the production of fuels and chemicals. Optical coatings for window glass. Electrodes for batteries and fuel cells. Corrosion-resistant coatings for the protection of metals and ceramics. Surface active agents, or surfactants, for use in tertiary oil recovery and the production of polymers, paper, textiles, agricultural chemicals, and cement. 

Enzymes are nature s catalysts. For the moment it is sufficient to consider an enzyme as a large protein, the structure of which results in a very shape-specific active site (Fig. 1.3). Flaving shapes that are optimally suited to guide reactant molecules (usually referred to as substrates) in the optimum configuration for reaction, enzymes are highly specific and efficient catalysts. For example, the enzyme catalase catalyzes the decomposition of hydrogen peroxide into water and oxygen... 

Enzymes are proteins catalyzing all in vivo biological reactions. Enzymatic catalysis can also be utilized for in vitro reactions of not only natural substrates but some unnatural ones. Typical characteristics of enzyme catalysis are high catalytic activity, large rate acceleration of reactions under mild reaction conditions, high selectivities of substrates and reaction modes, and no formation of byproducts, in comparison with those of chemical catalysts. In the field of organic synthetic chemistry, enzymes have been powerful catalysts for stereo- and regioselective reactions to produce useful intermediates and end-products such as medicines and liquid crystals. ... 

The pathway of the metabolic process converting the original nutrients, which are of rather complex composition, to the simple end products of COj and HjO is long and complicated and consists of a large number of intermediate steps. Many of them are associated with electron and proton (or hydrogen-atom) transfer from the reduced species of one redox system to the oxidized species of another redox system. These steps as a rule occur, not homogeneously (in the cytoplasm or intercellular solution) but at the surfaces of special protein molecules, the enzymes, which are built into the intracellular membranes. Enzymes function as specific catalysts for given steps. 

Y. Mozhaev, I. Berezin, and K. Martinek, Structure stability relationship in proteins Fundamental tasks and strategies for the development of stabilized enzyme catalysts for biotechnology, CRC Crit. Rev. Biochem., 23, 235 (1988). 

Enzymes are useful catalysts for a broad diversity of chemical reactions that enable the synthesis of natural and unnatural highly pure pharmaceutically active compounds. However, proteins themselves can also be the pharmaceutical ingredients. 

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). 

There are further theoretical objections to this RNA-world hypothesis, especially since we know of no organisms based on RNA without DNA and proteins. Moreover, RNA is not able to act as a catalyst for many essential simple molecule reactions, e.g. of CO, H2, N2, nor for most oxidation/reduction changes, and RNA... 

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