Enzyme irreversible changes

Conversely, controlled immobilization of enzymes at surfaces to enable high-rate direct electron transfer would eliminate the need for the mediator component and possibly lead to enhanced stability. Novel surface chemistries are required that allow protein immobilization with controlled orientation, such that a majority of active centers are within electrontunneling distance of the surface. Additionally, spreading of enzymes on the surfaces must be minimized to prevent deactivation due to irreversible changes in secondary structure. Finally, structures of controlled nanoporosity must be developed to achieve such surface immobilization at high volumetric enzyme loadings. 

A variety of responses can be initiated by the direct interaction of metals with cellular components. Membrane damage and enzyme inhibition are examples of such a metal effect. Above a certain threshold concentration of metals in the cell, its physiological state is irreversibly changed (Van Assche et al., 1988). This response is reflected by an increase in capacity (activity under non-limiting substrate and coenzyme concentrations) of certain enzymes. This increase in capacity is generally called enzyme induction. These secondary, indirect effects of metals are considered to play an important role in the stress metabolism induced by toxic metal concentrations. 

Bph. Enzymes in the Bph QA- state accumulates at 100 K and undergo an irreversible change between 100 K and 200 K. It was shown (Kotel nikov et al., 1983b Likhtenshtein, 1993) that within this temperature range the phosphorence probes detect animation of millisecond dynamics in the RC. 

Irreversibility. The reasoning given above is also an oversimplification in another sense. Most of the results discussed concern loss of biological (e.g., enzyme) activity, and the activities then are determined after cooling to room temperature. It thus concerns an irreversible change, rather than reversible unfolding. The simplest case would be... 

This includes both reversible changes like phosphorylation of specific serines in the enzymes of glycogen metabolism and irreversible changes like zymogen activation by proteolysis in digestion and blood clotting. These mechanisms are considered in more detail below. 

Another important factor that causes a decrease in the lipase activity is the depressurization rate, which is a step commonly used to separate the products. It has been reported that lipase activity decreases with an increase in the number of depressurizations (GieBauf et al., 1999). A rapid release of dissolved CO2 in the water bound to the enzyme may cause structural change to the enzyme (Lin et al., 2006). This irreversible change with depressurization was studied by Randolph et al. (1991). However, this problem is only encountered in the batch system and results in enzyme inactivation. In continuous flow systems, however, the depressurization step takes place after the product leaves the reactor. Immobilized lipases are retained inside the reactor and not exposed to depressurization. 

Heat-inactivation is ascribed to irreversible changes in the colloid enzyme comparable with the heat-coagulation of higher proteins. 

Drake and Baltz, 1976). The instability of DNA and the occurrence of mutations is considered briefly in Section II. The ability of DNA to denature (unwind) is essential, on the one hand, for replication and in order to serve as a template for RNA synthesis, and, on the other hand, may lead to irreversible changes. This ability is similar to the conform-ability of enzymes, which is essential for enzymatic action but which may lead to irreversible denaturation. 

Denaturation is accompanied by changes in both physical and biological properties. Solubility is drastically decreased, as occurs when egg white is cooked and the albumins unfold and coagulate. Most enzymes also lose all catalytic activity when denatured, since a precisely defined tertiary structure is required for their action. Although most denaturation is irreversible, some cases are known where spontaneous renaturation of an unfolded protein to its stable tertiary structure occurs. Renaturation is accompanied by a full recovery of biological activity. 

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