Enzymes inactivation, kinetics

Mechanism-based enzyme inactivation kinetics refers to the irreversible inhibition of an enzyme via a catalytically formed reactive intermediate that binds covalently (typically) to the enzyme active site prior to release and causes permanent inactivation of the enzyme. This type of inhibition is also known as... 

As an example of the first strategy outlined above, the simulation of sequential batch operation with immobilized penicillin acylase is presented. Penicillin acylase is inhibited by both products, being phenylacetic acid a competitive inhibitor and 6-aminopenicillanic acid a non-competitive inhibitor (lllanes et al. 1994). Simulation was done by solving differential Eq. 5.6, which represents the material balance with the corresponding kinetic expression (Eq. 3.43), and Eq. 5.76, which represents the two-phase series type enzyme inactivation kinetics. The scheme for this situation is presented in Fig. 5.20. 

Denys, S., van Loey, A.M., and Hendrickx, M.E. (2000) A modelling approach for evaluation process uniformity during batch high hydrostatic pressure processing combination of a numerical heat transfer model and enzyme inactivation kinetics. Innovative... 

Modification of the single SH group by NEM or PCMB has no effect on EcoRI activity (68). However, DTNB treatment gives a marginal reduction in activity. Specific modification of Lys by methyl acetimidate results in inactivation of the enzyme. Inactivation kinetics display two classes of modifiable Lys residues. The modification of the more sensitive class and consequent partial inactivation can be prevented by binding of either specific or nonspecific DNAs to the enzyme, in the presence or absence of Mg . ... 

Complex inactivation kinetics caused by enzyme-catalyzed decomposition of epoxide kinetic constants calculated from initial rates of inactivation. Approximate value calculated from half-life in the presence of 50 mAf inhibitor. 

In addition to the TDI experiment, the partition ratio measures the TDI efficiency. Specifically, the partition ratio is the number of inactivation kinetic events (k nact) versus the number of substrate turnover events per unit enzyme (kcat) [161], Thus, the most potent partition ratio is zero. The most common experimental setup for determining the partition ratio is the titration method that increases the inhibitor concentration relative to a known amount of enzyme. After the incubations, a secondary incubation containing a probe substrate similar to the TDI experiment is used to define the remaining activity. For accurate determination of the partition ratio from the titration method, it is assumed that the inhibitor is 100% metabolized ... 

The synthesis of suicide inhibitors and the kinetics of enzyme inactivation have greatly advanced the study of enzyme mechanisms as well as the design of drugs and antimetabolites. 

Selected entries from Methods in Enzymology [vol, page(s)] Activation of lipolytic enzymes by interfaces, 64, 341 model for lipase action on insoluble lipids, 64, 345 interfacial enzyme inactivation, 64, 347 reversibility of the adsorption step, 64, 347 monolayer substrates, 64, 349 kinetic models applicable to partly soluble amphiphilic lipids, 64, 353 surface dilution model, 64, 355 and 364 practical aspects, 64, 357. 

In order to describe and optimize the reverse micellar extraction process, Dekker et al. [ 170] have proposed a mathematical model, which satisfactorily describes the time dependency of the concentration of active enzyme in all the phases, based on the flow, mass transfer, and first-order inactivation kinetics. For each phase, a differential equation is derived. For forward extraction ... 

The design of real reactors, taking into account the diffusion, axial dispersion and enzyme inactivation effects, is described in the following sections, considering Michaelis-Menten kinetics as a model. These models are veiy important in predicting and simulating bioreactor performance and in modeling future processes. Also, for control purposes they are indispensable. 

Solutions of acid phosphatase are particularly sensitive to surface inactivation. Figure 3 (88) shows the inactivation rate of the enzyme in the presence and absence of surface-active detergents. The inactivation process is temperature sensitive and the protection by detergent is total. Most of the enzyme inactivation proceeds with first-order kinetics. A variety of agents—gelatin, bovine serum albumin, egg albumin, and Tween-80—protect the enzyme against inactivation. 

TNP-amino acids 45). Various levels of TNBS were then reacted with the enzyme, and the inactivation kinetics were analyzed in terms of a multi-order reaction, according to the treatment of Levy et of. (47)... 

When the enzyme is inactivated by heating in the presence or absence of Mg2+, the inactivation kinetics of the three activities are indistinguishable (Fig. 7). 

We have shown that there is good agreement between dissociation constants obtained by kinetic studies, and by measurements of the substrate-induced enzyme inactivation (4) the latter may yield true equilibrium constants, as is the case for Kj determinations, free from kinetic variables that may be present in estimations of Km (6). However, the constants determined by inducing inactivations cannot be accepted without properly evaluating other factors (14). 

---