Effects on Enzyme Activity

Regulatory or allosteric enzymes like enzyme 1 are, in some instances, regulated by activation. That is, whereas some effector molecules such as F exert negative effects on enzyme activity, other effectors show stimulatory, or positive, influences on activity. 

Glycogen synthase also exists in two distinct forms which can be interconverted by the action of specific enzymes active, dephosphorylated glycogen synthase I (glucose-6-P-independent) and less active phosphorylated glycogen synthase D (glucose-6-P-dependent). The nature of phosphorylation is more complex with glycogen synthase. As many as nine serine residues on the enzyme appear to be subject to phosphorylation, each site s phosphorylation having some effect on enzyme activity. 

Olea, D. and Faure, C. (2003) Quantitative study of the encapsulation of glucose oxidase into multilamellar vesicles and its effect on enzyme activity. Journal of Chemical Physics, 119, 6111-6118. 

Mn2+ active transport system in Staphylococcus aureus. These metal-microbe interactions result in decrease microbial growth, abnormal morphological changes, and inhibition of biochemical processes in individual (Akmal et al. 2005a,b). The toxic effects of metals can be seen on a community level as well. In response to metal toxicity, overall community numbers and diversity decrease. Soil is a living system where all biochemical activities proceed through enzymatic processes. Heavy metals have also adverse effects on enzyme activities (Fig. 1). 

In addition to its direct effect on enzyme activity in the cytosol of target cells, cAMP can also initiate gene expression without actually entering the nucleus. PKA may also... 

The hydrogen ion concentration has an effect on enzyme activity because many of the amino acid groups in an enzyme bear ionisable groups. Changes in pH will alter the degree of ionisation of some of these groups and so affect the ionisation of the enzyme molecule as a whole, modifying enzyme activity in at least three ways ... 

Early attempts to purify the enzyme brought the quick realization that aconitase is easily inactivated (6,7). In the early 1950 s Dickman and Qoutier (8,9) found that inactivated aconitase could be reactivated by incubation with iron and a reduc-tant. From kinetic analyses of the iron and reductant effects on enzyme activity, Morrison argued that both formed Michaelis-Menten complexes wiA the enzyme (10). This refuted the earlier idea that the sole role of the reductant was to maintain iron in a reduced state (9). Of several metal cations tried, only ferrous ion was found to be capable of this reactivation process (8,11). Because of the absolute requirement for iron in activation, the known chelation properties of citrate, and Ogston s 3-point attachment proposal, Speyer and Dickman proposed that the active site iron provides three coordination sites for substrate binding - one for hydroxyl and two for carboxyl groups (12). 

The increase in energy content of an atom, ion, or molecular entity or the process that makes an atom, ion, or molecular entity more active or reactive. In enzymology, activation often refers to processes that result in increased enzyme activity. For example, increasing temperature often can have a positive effect on enzyme activity (See Arrhenius Equation). Other examples of enzyme activation include (1) proteolysis of zymogens (2) alterations in ionic strength (3) alterations due to pH changes (4) activation in cooperative systems (5) lipid or membrane interface activation (6) metal ion effects (7) autocatalysis and (8) covalent modification. 

These observations reveal that enzyme hydration below monolayer values has an effect on enzyme activity, and in some cases such activation can be dramatic. However, in all these examples, water was added and this may not be appropriate where nearly anhydrous reaction conditions are necessary. 

Following these considerations, the pH of these systems was actively controlled by the addition of inorganic salts (acids or bases) [51]. As a matter of fact, a 20-fold increase in the initial rate could be observed upon addition of KHC03 or K2C03 in the synthesis of Z-L-Asp-L-Phe-OMe, but 1.5 equivalents of salt were optimal to obtain yields of more than 90%. The profile of initial rate as a function of K2C03 concentration displayed a bell-shaped figure typically seen for pH effects on enzyme activity (Figure 12.3). 

Munday, M.R. Hardie, D.G. Isolation of three cyclic-AMP-independent acetyl-CoA carboxylase kinases from lactating rat mammary gland and characterization of their effects on enzyme activity. Eur. J. Biochem., 141, 617-627 (1984)... 

Whether an inhibitor acts in a competitive or noncompetitive manner is deduced from a Lineweaver-Burk or direct linear plot using varying concentrations of inhibitor and substrate. In separate assays, two substances will be added to the dopa-tyrosinase reaction mixture, and the effect on enzyme activity will be quantified. The structures of the potential inhibitors, cinnamic acid and thiourea, are shown in Figure E5.9. The inhibition assays must be done immediately following the KM studies. To measure inhibition, reaction rates both with and without inhibitor must be used and the tyrosinase activity must not be significantly different. If it is necessary to do the inhibition studies later, the Ku assay for L-dopa must be repeated with freshly prepared tyrosinase solution. 

Glick et al. (134) and Goren and Barnard (135, 136) have shown that in the alkylation reaction with bromoacetate ion the principal alkylation at histidine occurs as described below but that in addition Met 30 is alkylated. This modification has no effect on enzymic activity and is not affected by the histidine alkylations. Phosphate and sulfate do not inhibit the reaction but pyrophosphate and 2 -CMP do. 

Most literature on enzyme kinetics is devoted to initial rate data and the analysis of reversible effects on enzyme activity. In many applications and process settings, however, the rate at which the enzyme activity declines is of critical importance. This is especially true when considering its long-term use in continuous reactors. In such situations the economic feasibility of the process may hinge on the useful lifetime of the enzyme biocatalyst. The focus of this section is on the mechanisms and kinetics of loss of enzyme activity. It should also be recognised that the alteration of protein structure is central to the practical manipulation of proteins (e.g. precipitation, affinity and other forms of protein chromatography, and purification in general). 

The Effect on Enzyme Activity and Some Biochemical Reactions. .. 89... 

Smith, J. Paranormal effects on enzyme activity. Proc. Para-... 

In this application, the use of wild-type electric eel AChE and a recombinant AChE, specifically selected as very sensitive to dichlorvos, was compared. The effect of the matrix extract was determined by using various sample solvent ratios, 1 2.5, 1 5, 1 10, and 1 20. The optimal extraction ratio, considering the electrochemical interferences and the effect on enzyme activity and bioavailability of the pesticide, was 1 10. 

Enzyme Effects on enzymic activity and immunoreactivity Reference... 

An effect on enzyme activity, an inhibition or stimulation depending on the enzyme and its source. 

Table 2 presents the results obtained in the statistical modeling. Temperature and reduced density had a pronounced effect on enzyme activity loss, both showing a positive effect. At this point, it is important to mention that the cross-interaction temperature-exposure time had a significant negative effect. In the range investigated (10-200 kg/[m3-min]), the decompression rate had a weak negative effect on loss of enzyme activity. The same effect was observed with the exposure time (60-360 min). 

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