Protein enzyme activities

In this chapter, the utilization of the Mb framework for the introduction or alternation of protein-enzyme activities has been reviwed. Especially, enatio-selective oxidation of sulfides and olefins are highlighted. More importantly, it addresses the importance of design of the protein active site and the prosthetic group for the construction of artifical enzymes exhibiting high activities and selectivities. 

Although enzymes are considered to be proteins, enzyme activity has re-. ... 

For most enzymes, catalytic activity is temperature-dependent to a maximum level, above whioh they lose their activity. Also, by analogy with other proteins, enzymes are stable only within a limited range of pH. Outside this range, enzymes are denatured by ohanges in the charges of ionizable amino acid residues that alter the tertiary structure of proteins. Enzyme activity reaches a peak or a plateau at a specific pH, so enzymatic digestion is usually performed in a buffered medium. The process is also affected by the enzyme concentration, which must therefore be optimized as well. 

Although enzymes are considered to be proteins, enzyme activity has recently been found in ribonucleic acid (RNA) in certain organisms. These ribozymes may yield clues to the origins of life on Earth. DNA needs... 

Metabotropic receptors G protein-coupled receptors that respond to neurotransmitters either by a direct action of G proteins on ion channels or by G protein enzyme activation that leads to formation of diffusible second messengers... 

Biological activity Proteins Enzyme activity variable... 

The challenge in proteomics is to learn how final protein structures are formed, and the steps involved in their formations. With that knowledge, important proteins can be synthesized in the lab and in industry, improvements in protein enzyme activity can be attempted, and the proteins derived from genetic deficiencies may be able to be corrected. Protein study challenges are listed in Chen and Sivachenko (2005). 

Suppression of peroxidase and catalase activity is of importance for the shelf life of heat-processed food. As long as the protein moiety has not been denatured, it is the lipoxygenase enzyme which is the most active for lipid peroxidation (cf. 3.7.2.2). After lipoxygenase activity is destroyed by heat denaturation, its role is replaced by the heme(in) proteins. As already suggested, an assay of heme(in) protein enzyme activity does not necessarily reflect its prooxidant activity. 

Potassium is required for enzyme activity in a few special cases, the most widely studied example of which is the enzyme pymvate kinase. In plants it is required for protein and starch synthesis. Potassium is also involved in water and nutrient transport within and into the plant, and has a role in photosynthesis. Although sodium and potassium are similar in their inorganic chemical behavior, these ions are different in their physiological activities. In fact, their functions are often mutually antagonistic. For example, increases both the respiration rate in muscle tissue and the rate of protein synthesis, whereas inhibits both processes (42). 

Specificity for a particular charged substrate can be engineered into an enzyme by replacement of residues within the enzyme-active site to achieve electrostatic complementarity between the enzyme and substrate (75). Protein engineering, when coupled with detailed stmctural information, is a powerful technique that can be used to alter the catalytic activity of an enzyme in a predictable fashion. 

Reverse transcriptase (from avian or murine RNA tumour viruses) [9068-38-6] [EC 2.7.7.49]. Purified by solubilising the virus with non-ionic detergent. Lysed virions were adsorbed on DEAE-cellulose or DEAE-Sephadex columns and the enzyme eluted with a salt gradient, then chromatographed on a phosphocellulose column and enzyme activity eluted in a salt gradient. Purified from other viral proteins by affinity chromatography on a pyran-Sepharose column. [Verna Biochim Biophys Acta 473 1 7977 Smith Methods Enzymol 65 560 1980 see commercial catalogues for other transcriptases.]... 

The second protein in the membrane of influenza vims, neuraminidase, does not belong to any of these three groups of barrel structures. Instead, it forms a propeller-like structure of 24 p strands, arranged in six similar motifs that form the six blades of the propeller. Each motif is a p sheet of 4 up-and-down-connected p strands. The enzyme active site is formed by loop regions on one side of the propeller. 

Specific enzyme activity Amount of substrate rendered into product per unit dry weight of enzyme protein per unit time. 

FIGURE 2.16 pH versus enzymatic activity. The activity of enzymes is very sensitive to pH. The pH optimum of an enzyme is one of its most important characteristics. Pepsin is a protein-digesting enzyme active in the gastric fluid. Trypsin is also a proteolytic enzyme, but it acts in the more alkaline milieu of the small intestine. Lysozyme digests the cell walls of bacteria it is found in tears. 

Nonrepetitive but well-defined structures of this type form many important features of enzyme active sites. In some cases, a particular arrangement of coil structure providing a specific type of functional site recurs in several functionally related proteins. The peptide loop that binds iron-sulfur clusters in both ferredoxin and high potential iron protein is one example. Another is the central loop portion of the E—F hand structure that binds a calcium ion in several calcium-binding proteins, including calmodulin, carp parvalbumin, troponin C, and the intestinal calcium-binding protein. This loop, shown in Figure 6.26, connects two short a-helices. The calcium ion nestles into the pocket formed by this structure. 

Regulation of enzyme activity is achieved in a variety of ways, ranging from controls over the amount of enzyme protein produced by the cell to more rapid, reversible interactions of the enzyme with metabolic inhibitors and activators. Chapter 15 is devoted to discussions of enzyme regulation. Because most enzymes are proteins, we can anticipate that the functional attributes of enzymes are due to the remarkable versatility found in protein structures. 

The second enzyme to be crystallized (byjohn Nordrrnp in 1930). Even more than nrease before it, pepsin. study by Northrnp established tirat enzyme activity comes from proteins. fAiso known as rennin, it is tire major pepsinlike enzyine in gastric Jnice of fetal and newborn animals. 

FIGURE 18.40 The glutamyl carboxylase reaction is vitamin K-dependent. This enzyme activity is essential for the formation of 7-car-boxyglutamyl residues in several proteins of the blood-clotting cascade (Figure 15.5), accounting for the vitamin K dependence of coagulation. 

The serine residue of isocitrate dehydrogenase that is phos-phorylated by protein kinase lies within the active site of the enzyme. This situation contrasts with most other examples of covalent modification by protein phosphorylation, where the phosphorylation occurs at a site remote from the active site. What direct effect do you think such active-site phosphorylation might have on the catalytic activity of isocitrate dehydrogenase (See Barford, D., 1991. Molecular mechanisms for the control of enzymic activity by protein phosphorylation. Bioehimiea et Biophysiea Acta 1133 55-62.)... 

In 1984, Magnuson et al. (Entry 1) investigated the influence of ethylammoni-um/water mixtures on enzyme activity and stability [29]. At low [H3NEt][N03] concentrations, an increased activity of alkaline phosphatase was found. The same ionic liquid was used by Flowers and co-workers, who found improved protein refolding after denaturation (Entry 2) [30]. 

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