Enzyme activity, control

Loss of the Activity and the Change in Primary Structure, Ozone causes the loss of enzymic activity in lysozyme as shown in Figure 1, The enzyme is inactivated linearly until the activity is reduced to 5%, Prolonging exposure of lysozyme to ozone causes further decrease in enzymic activity. Control experiments, using gas streams without ozone, were carried out in the same conditions and over the same periods. Figure 2 shows that the activity of both control and ozonized lysozyme varies with pH change. Although the ozonized product shows more extensive dependence on pH than the native one, the optimum is the same. 

Westerhoff, H. V. Chen, Y. D. How do enzyme activities control metabolite concentrations An additional theorem in the theory of metabolic control. Eur J Biochem 1984,142 425-430. 

Because modulation of enzyme activities depends on metabolite concentrations, which in turn are determined by the entire metabolic network, the overall response time for these controls can be on the order of seconds. This is the same as the time scale for changes in environmental conditions (e.g., pH, dissolved oxygen concentration) encountered by cells as they circulate through the nonuniform contents of a large-scale bioreactor. Therefore, beyond the complexities of enzyme activity control in the steady state, dynamic properties of this control system are important. The circulation pattern in a bioreactor has major effects on product formation [28]. Lack of understanding of transient responses of cell metabolism is one central obstacle to systematic scale-up of laboratory results (obtained in idealized,... 

With these considerations, we primarily review the biological activities of essential oils for enzyme activity control, antiallergy and antimicrobial efficacy. 

TABLE 16.3 Enzyme inhibition kinetics from the kinetic model in Scheme 16.1 types of enzyme inhibition, velocity and % of enzyme activity (% Control) for the metabolism of substrate (S) in the presence of an inhibitor (I), and relationship between [S] and [1] in different types of inhibition as [S] = Kq,. 

Fig. 5. Effect of HCOj -free medium on inactivation and phosphorylation of acetyl-CoA carboxylase. Enzyme preparation was placed in the main compartment of a Warburg flask, capped with a serum stopper, containing a small piece of Whatman filter paper (2x3 cm) plus 0.1 ml of Hyamine 10-X in the central well. Vessels were evacuated and refilled with COj-free Nj several times. This procedure was repeated several times during a 3-hour period at room temperature to completely remove dissolved HCOs firom the medium. Enzjmie preparation was equilibrated at 37°C for 10 minutes prior to the addition of [y- PlATP (specific activity, 28 iiCi/iimole at 0.7 miW final concentration) which was also treated in a similar way to remove COi. AT indicated times, P incorporation was terminated by addition of a cold solution containing ATP and EDTA at 5 times the concentrations of [y- PlATP and MgCl2, respectively. The labeled en me was purified by DE AE-cellulose chromatography as described before, and immunoprecipitation of the enzyme was carried out by incubation with rabbit antibody to the carboxylase for 15 minutes and with the membrane preparation fromS. aureus (18) for another 15 minutes. Enzyme-antibody precipitates were collected and immediately washed by centrifugation. Enzyme activity-control enzyme -ATP, O +ATP, . COj-free enzyme —ATP, A -H ATP, . Radioactivily-control enzyme, C02-free enzyme, . From Lent et al. (71).

Attachment of a polymer bearing additional epoxy groups on an amine-modified gold electrode. (Reprinted with permission from Nagel et al. 2007. Enzyme activity control by responsive redoxpolymers. Langmuir 23 (12) 6807-6811, copyright (2007) American Chemical Society.)... 

Nagel B, Warsinke A, Katterle M (2007) Enzyme activity control by responsive redoxpolymers. Langmuir 23 6807-6811... 

In fact, most RIAs and many nonisotopic immunoassays use a competitive binding format (see Fig. 2). In this approach, the analyte in the sample to be measured competes with a known amount of added analyte that has been labeled with an indicator that binds to the immobilized antibody. After reaction, the free analyte—analyte-indicator solution is washed away from the soHd phase. The analyte-indicator on the soHd phase or remaining in the wash solution is then used to quantify the amount of analyte present in the sample as measured against a control assay using only an analyte-indicator. This is done by quantifying the analyte-indicator using the method appropriate for the assay, for example, enzyme activity, fluorescence, radioactivity, etc. 

Enzyme Assays. An enzyme assay determines the amount of enzyme present in sample. However, enzymes are usually not measured on a stoichiometric basis. Enzyme activity is usually determined from a rate assay and expressed in activity units. As mentioned above, a change in temperature, pH, and/or substrate concentration affects the reaction velocity. These parameters must therefore be carefully controlled in order to achieve reproducible results. 

Figure 1.20). All of these reactions, many of which are at apparent crosspurposes in the cell, must be fine-tuned and integrated so that metabolism and life proceed harmoniously. The need for metabolic regulation is obvious. This metabolic regulation is achieved through controls on enzyme activity so that the rates of cellular reactions are appropriate to cellular requirements. 

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. 

List six general ways in which enzyme activity is controlled. 

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.)... 

Entries 7, 8, and 10 describe so-called Idnetically controlled syntheses starting from activated substrates such as ethyl esters or lactose. In two reaction systems it was possible to demonstrate that ionic liquids can also be useful in a thermodynamically controlled synthesis starting with the single components (Entry 11) [39]. In both cases, as with the results presented in entry 6, the ionic liquids were used with addition of less than 1 % water, necessary to maintain the enzyme activity. The yields observed were similar or better than those obtained with conventional organic solvents. 

Enzyme activity in organic solvents depends on parameters such as water activity, pH control, substrate-product solvation, enzyme form, and nature of the solvent. 

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