Enzyme activity, catalytic

Enzyme Sta.bihty, Loss of enzyme-catalytic activity may be caused by physical denaturation, eg, high temperature, drying/freezing, etc or by chemical denaturation, eg, acidic or alkaline hydrolysis, proteolysis, oxidation, denaturants such as surfactants or solvents, etc. pH has a strong influence on enzyme stabiHty, and must be adjusted to a range suitable for the particular enzyme. If the enzyme is not sufficiendy stable in aqueous solution, it can be stabilized by certain additives a comprehensive treatment with additional examples is available (27). 

From the results of the urease activity test summarized in Figure 15, it is clear that the deposition procedure preserved to a certain extent the enzyme catalytic activity. Heating the sample before testing decreased the enzyme in the film by about 30% but did not eliminate it completely. The results of the activity test of two samples are summarized in Table 1 together with reference values for a spontaneous reaction without enzyme. It is necessary to underline that enzymatic activity on spherical supports was higher than the respective value in flat films, which could indicate that apparent catalytic efficiency was improved due to an increased area-to-volume ratio. 

It is worth mentioning that membrane-bound forms of GC, which can be considered signal transducing enzymes , are structurally homologous to other signal transducing enzymes, such as certain protein tyrosine kinases and phosphatases, which also possess receptor moieties in their extracellular (amino terminus) domain and enzyme catalytic activity in their intracellular domain (see Ch. 24). Activation of many of these receptors occurs upon ligand-induced dimerization of the receptors, and a similar... 

Fig. 1 Graphical representation shows immobilized enzyme catalytic activity and their recovery after the completion of the catalytic reaction using a simple magnet.

Henderson GL, Harkey MR, Gershwin ME et al (1999) Effects of ginseng components on cDNA-expressed cytochrome P450 enzyme catalytic activity. Life Sci 65 209-214... 

A unit of enzyme catalytic activity equal to the conversion of one mole of substrate per second in a specified assay system. The katal (kat) is more commonly used in clinical enzymology. One unit of enzyme activity (i.e., one micromole per minute) corresponds to 16.67 nkat. 

The most straightforward way to quantify the amount of water in a reaction mixture is to use the water concentration (in molL-1 or % by weight or volume). However, the properties of the enzyme (catalytic activity, etc.) are much more... 

TOPII (inhibits enzyme catalytic activity) [apoptotic, cytotoxic] TOPII (by formation of cleavable TOPII-DNA complex) (DNA, MLCK, PKA)... 

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. 

Solvent Type The affect of different organic solvents on various enzyme catalytic activities has been demonstrated (37). From a mechanistic standpoint, the effect of organic solvents on enzyme catalysis is still debated (38). Conformational changes in enzymes, when suspended in organic solvents, have been reported to result in alteration of substrate specificity and affinity of substrates for enzymes (39). The polarity of organic solvents affects lipase-catalyzed reactions as do other variables that are critical to enzyme activity in organic media. The nature of the... 

Tramontane, A., and Schloeder, D. Production of antibodies that mimic enzyme catalytic activity. Methods Enzymol 178 531-550, 1989. 

Zou, L., Harkey, M.R. and Henderson, G.L. (2002) Effects of herbal components on cDNA-expressed cytochrome P450 enzyme catalytic activity. Life Sciences, 71, 1579-1589-Zung, W.W.K. (1965) A self-rating depression scale. Archives of General Psychiatry, 12, 63—IQ-... 

Since the purity and molecular weight of many enzymes are not known, the amount of enzyme is usually characterized by a specific activity , i.e. units of enzyme catalytic activity per milligram of protein, where a unit of activity is something like the transformation of l.O/zmol (10 mol) substrate/mg enzyme preparation per minute. 

The most striking effects in micellar enzymology are seen in dependencies of enzyme catalytic activity, k at, on surfactant degree of hydration. These dependencies are normally bell shaped (see examples in Fig. 5) the higher the molecular weight of the enzyme the... 

FIG. 11 Combination of two factors regulating enzyme catalytic activity variation in the surfactant concentration and addition of water-miscible organic solvents, (a) Peroxidase in the system AOT-water/glycerol-octane at water/glycerol volume ratios (O) 100 0 ( ) 20 80. (b) a-Chymotrypsin in the system AOT-water/glycerol-octane at water/glycerol volume ratios (O) 100 0 ( ) 6 94. Dashed lines show the catal5dic activities of the enzymes in aqueous solution. (From Ref. 44.)... 

Regulatory enzymes Catalytic activities of enzymes are subject to various types of regulations (Hannnes, 1982). Enzymes that are subjected to metabolic regulations are commonly referred to as regulatory enzymes. 

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