Enzyme deactivation protein unfolding

Fig. 9.54 Deactivation of enzymes by protein unfolding. (From https //upload.wikimedia.orgfyirikipedia/ commons/ /I d/Process of Denaturation.svg).

Although very interesting biotranformations have been reported in supercritical carbon dioxide, this solvent has been found to affect enzyme activity adversely. CO can react reversibly with free amino groups (lysine residues, specifically) on the surface of the protein to form carbamates, leading to low activity enzyme. [21]. Furthermore, carbon dioxide dissolves in water at molar concentrations at moderate pressures (<100 bar) and rapidly forms H COj. This can create some problems in biocatalytic reactions because many enzymes are denatured (unfolded and/or deactivated) at low pH. Enzymes can also be denatured by pressurization/depressuriza-tion cycles. For all of them, it is necessary to develop new enzyme stabilization strategies. 

Thus, with reference to lipase, it seems that loss of water molecules from the microenvironment of the enzyme structure may not be the key for destabilization or deactivation of the enzyme since lipase is fairly stable under anhydrous condition. However, H-bonding nature of the component ions of ILs might be important for maintaining the integrity of the native conformation of the enzyme. At the same time, too strong H-bond could be detrimental due to the disruption of key H-bonds responsible for maintaining native structure which leads to the collapse of the protein framework or unfolding of the protein. 

Recovered activity and immobilization yield were calculated, and results are listed in Table 1. It can be observed that recovered activity increased when the initial enzyme concentration in the supernatant (Eq) was increased to 60 and 90 U/ml, but it remained almost constant for the other concentrations studied. Immobilization yield, on the other hand, decreased when high concentrations of enzyme were used (60 to 150 U/ml, compared to 30-40 U/ml). When Ef,=9Q U/ml, the highest value of recovered activity was obtained, which suggests that protein molecules are probably immobilized at close proximity to each other, which may prevent deactivation caused by enzyme unfolding by covering the support surface. In other words, when enzyme load was increased, more enzyme molecules were immobilized and less area of the support is available for lipase to spread itself, which may prevent loss in activity [31]. 

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