General Characteristics of Enzymes

Parkin, K.L. 1993. General characteristics of enzymes. In Enzymes in food processing, ed. T. Nagodawithana and G. Reed. San Diego, CA Academic Press, Inc. 

In this section, general characteristics of enzyme catalysis are briefly mentioned and then the functions of chymotrypsin and lysozyme are discussed as two specific examples of the hydrolytic enzyme. 

Describe the general characteristics of enzymes and explain why enzymes are vital in body chemistry. (Section 10.1)... 

The response characteristics of enzyme electrodes depend on many variables, and an understanding of the theoretical basis of their function would help to improve their performance. Enzymatic reactions involving a single substrate can be formulated in a general way as... 

General characteristics of the support to be considered are discussed in chapter 6 and those of relevance for the use of enzymes in non-conventional media are listed in Table 9.2. In addition, the specific surface area of the support is of special importance for the applications in non-conventional media. Inactivation can occur if the surface area is too large in relation to the amount of enzyme (Figure 9.3). In order to avoid inactivation at least a monolayer of enzyme molecules should be formed on the accessible surface (Wehtje, Adlercreutz and Mattiasson, 1993). For enzymes of high purity and high activity, the amount of enzyme needed is sometimes quite small. In such cases the enzyme can be mixed with a protecting protein before immobilisation to achieve at least a monolayer of protein and thereby avoid... 

C-0 bond cleavage in R-l-P and the absence of a phosphoryl enzyme intermediate appear to be general characteristics of PNP s from a wide variety of sources human erythrocytes, calf spleen and E. coli. 

Enzymes are biocatalysts, as such they facilitate rates of biochemical reactions. Some of the important characteristics of enzymes are summarized. Enzyme kinetics is a detailed stepwise study of enzyme catalysis as affected by enzyme concentration, substrate concentrations, and environmental factors such as temperature, pH, and so on. Two general approaches to treat initial rate enzyme kinetics, quasi-equilibrium and steady-state, are discussed. Cleland s nomenclature is presented. Computer search for enzyme data via the Internet and analysis of kinetic data with Leonora are described. 

Currently, immunoassay is the practical method of choice for measuring cytokines and their receptors. As cytolanes are proteins, specific antibodies can be raised against recombinant cytokines and have also been measured as an indicator of cytokine presence, The general characteristics of cytokine immunoassays are comparable with the classical immunoassays, with monoclonal, oligoclonal, or polyclonal antibodies all being used (see Chapter 9). The most popular formats are immunoradiometric assay (IRMA) and ELISA, which use a first monoclonal antibody for the capture and a second antibody labeled with a radioisotope or an enzyme. 

Table 1 summarizes the general characteristics of representative urease, hydrogenase and CODHs. As it will be further discussed below, the X-ray structures of only two Ni-containing proteins, urease and hydrogenase, are known [16, 17]. The former has the well known triose phosphate isomerase (TIM) barrel topology (Fig. 1) whereas the latter displays a so far unique folding (Fig. 2). The next challenge will be the elucidation of the crystal structures of the CODH/ACS enzyme of Clostridium thermoaceticum and of the simpler CODH from Rhodospirillum rubrum. 

Extreme caution must be used in interpreting the experimental data obtained from studies of the site-specific modification of enzyme sites. For an enzyme whose structure has been determined by X-ray crystallography, such as bovine pancreatic ribonuclease, the results of affinity labeling by a reactive nucleoside can be compared with the crystal structures of various enzyme-ligand complexes (271). The general characteristics of the haloacetyl class of affinity labels have been summarized (281). 

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